Biology Final Study 1-20

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T/F: The number and location of mitochondria within a cell can change, depending on both the cell type and the amount of energy required.

True

T/F: The oxidation of sugar is an energetically favorable process

True

T/F: The pyruvate dehydrogenase complex catalyzes three different, but linked, enzymatic reactions.

True

T/F: Transporters undergo transitions between different conformations, depending on whether the substrate-binding pocket is empty or occupied.

True

T/F: Under anaerobic conditions, the ATP synthase can hydrolyze ATP instead of synthesizing it.

True

Proteins that are fully translated in the cytosol do not end up in _______. (a) the cytosol. (b) the mitochondria. (c) the interior of the nucleus. (d) transport vesicles.

T/F: Voltage-gated Na+ channels become automatically inactivated shortly after opening, which ensures that the action potential cannot move backward along the axon

True

T/F: With respect to the amount of energy stored in molecules of the body, 6 g of glycogen is the equivalent of 1 g of fat

True

Which of the following are examples of isomers? (a) glucose and galactose (b) alanine and glycine (c) adenine and guanine (d) glycogen and cellulose

1-16 Water molecules readily form hydrogen bonds with other polar molecules, and when they encounter nonpolar molecules they must form hydrogen-bonding networks with neighboring water molecules. Which of the following molecules will cause a "cage" of water to form? (a) 2-methylpropane (b) acetone (c) methanol (d) urea

(a) 2-methylpropane

Which of the following statements is false? (a) A mutation that arises in a mother's somatic cell often causes a disease in her daughter. (b) All mutations in an asexually reproducing single-celled organism are passed on to progeny (c) In an evolutionary sense, somatic cells exist only to help propagate germ line cells (d) A mutation is passed on only if it is present in the germ line

(a) A mutation that arises in a mother's somatic cell often causes a disease in her daughter

Which of the following statements about gene families is false? (a) Because gene duplication can occur when crossover events occur, genes are always duplicated onto homologous chromosomes (b) Not all duplicated genes will become functional members of gene families (c) Whole genome duplication can contribute to the formation of gene families (d) Duplicated genes can diverge in both their regulatory and coding regions

(a) Because gene duplication can occur when crossover events occur, genes are always duplicated onto homologous chromosomes

19-25 Which of the following statements about meiosis is *true*? (a) During meiosis, the paternal chromosomes pair with the maternal chromosomes before lining up at the metaphase plate. (b) Unicellular organisms that have a haploid state undergo meiosis instead of mitosis during cell division. (c) Meiosis produces four genetically identical cells. (d) In general, meiosis is faster than mitosis.

(a) During meiosis, the paternal chromosomes pair with the maternal chromosomes before lining up at the metaphase plate.

which of the following statements about homologous genes is true? (a) For protein coding genes, homologous genes will show more similarity in their amino acid sequences than in their nucleotide sequences (b) Fewer than 1% of human genes have homologs in the nematode and the fruit fly (c) Most homologous genes arose by gene duplication

(a) For protein coding genes, homologous genes will show more similarity in their amino acid sequences than in their nucleotides sequences

The pufferfish, fugu rubripes, has a genome that is one-tenth the size of mammalian genomes. Which of the following is not a possible reason for this size difference? (a) Fugu has lost many genes that are part of gene families (b) intron sequences in Fugu are shorter than those in mammals (c) Fugu lacks the repetitive DNA found in mammals (d) The fugu genome seems to have lost sequences faster than it has gained them over evolutionary times

(a) Fugu has lost many genes that are part if gene families

7-33 Genes in eukaryotic cells often have intronic sequences coded for within the DNA. These sequences are ultimately not translated into proteins. Why? (a) Intronic sequences are removed from RNA molecules by the spliceosome, which works in the nucleus. (b) Introns are not transcribed by RNA polymerase. (c) Introns are removed by catalytic RNAs in the cytoplasm. (d) The ribosome will skip over intron sequences when translating RNA into protein.

(a) Intronic sequences are removed from RNA molecules by the spliceosome, which works in the nucleus.

Which of the following is true of a retrovirus but not the Alu retrotransoposion? (a) It encodes its own reverse transcriptase (b) it requires cellular enzymes to make copies (c) it can be excised and moved to a new location in the genome

(a) It encodes its own reverse transcriptase

Which of the statements about what we have learned by comparing modern-day human genome to other genomes is true? (a) Modern humans whose ancestors are from Europe or Asia share up to 4% of their genome with Neanderthals (b) The human genome is far more gene-dense than the yeast genome

(a) Modern humans whose ancestors are from Europe or Asia share up to 4% of their genome with Neanderthals

7-26 Transcription in bacteria differs from transcription in a eukaryotic cell because __________________________. (a) RNA polymerase (along with its sigma subunit) can initiate transcription on its own. (b) RNA polymerase (along with its sigma subunit) requires the general transcription factors to assemble at the promoter before polymerase can begin transcription. (c) the sigma subunit must associate with the appropriate type of RNA polymerase to produce mRNAs. (d) RNA polymerase must be phosphorylated at its C-terminal tail for transcription to proceed.

(a) RNA polymerase (along with its sigma subunit) can initiate transcription on its own.

8-50 In mammals, individuals with two X chromosomes are female, and individuals with an X and a Y chromosome are male. It had long been known that a gene located on the Y chromosome was sufficient to induce the gonads to form testes, which is the main male-determining factor in development, and researchers sought the product of this gene, the so-called testes- determining factor (TDF). For several years, the TDF was incorrectly thought to be a zinc finger protein encoded by a gene called BoY. Which of the following observations would most strongly suggest that BoY might not be the TDF? Explain your answer. (a) Some XY individuals that develop into females have mutations in a different gene, SRY, but are normal at BoY. (b) BoY is not expressed in the adult male testes. (c) Expression of BoY in adult females does not masculinize them. (d) A few of the genes that are known to be expressed only in the testes have binding sites for the BoY protein in their upstream regulatory sequences, but most do not.

(a) Some XY individuals that develop into females have mutations in a different gene, SRY, but are normal at BoY.

8-13 Which of the following statements about the Lac operon is false? (a) The Lac repressor binds when lactose is present in the cell. (b) Even when the CAP activator is bound to DNA, if lactose is not present, the Lac operon will not be transcribed. (c) The CAP activator can only bind DNA when it is bound to cAMP. (d) The Lac operon only produces RNA when lactose is present and glucose is absent.

(a) The Lac repressor binds when lactose is present in the cell.

8-44 You are studying a set of mouse genes whose expression increases when cells are exposed to the hormone cortisol, and you believe that the same cortisol- responsive transcriptional activator regulates all of these genes. Which of the following statements below should be true if your hypothesis is correct? (a) The cortisol-responsive genes share a DNA sequence in their regulatory regions that binds the cortisol-responsive transcriptional activator. (b) The cortisol-responsive genes must all be in an operon. (c) The transcriptional regulators that bind to the regulatory regions of the cortisol-responsive genes must all be the same. (d) The cortisol-responsive genes must not be transcribed in response to other hormones.

(a) The cortisol-responsive genes share a DNA sequence in their regulatory regions that binds the cortisol-responsive transcriptional activator.

11-28 A group of membrane proteins can be extracted from membranes only by using detergents. All the proteins in this group have a similar amino acid sequence at their C-terminus: -KKKKKXXC (where K stands for lysine, X stands for any amino acid, and C stands for cysteine). This sequence is essential for their attachment to the membrane. What is the most likely way in which the C-terminal sequence attaches these proteins to the membrane? (a) The cysteine residue is covalently attached to a membrane lipid. (b) The peptide spans the membrane as an α helix. (c) The peptide spans the membrane as part of a β sheet. (d) The positively charged lysine residues interact with an acidic integral membrane protein.

(a) The cysteine residue is covalently attached to a membrane lipid.

Which of the following statements is true? (a) The intron structure of most genes is conserved among vertebrates (b) the more nucleotides there are in a genome, the more genes there will be in its genome

(a) The intron structure of most genes is conserved among vertebrates

7-27 Which of the following does not occur before a eukaryotic mRNA is exported from the nucleus? (a) The ribosome binds to the mRNA. (b) The mRNA is polyadenylated at its 3′ end. (c) 7-methylguanosine is added in a 5′-to-5′ linkage to the mRNA. (d) RNA polymerase dissociates.

(a) The ribosome binds to the mRNA.

11-32 Porin proteins form large, barrel-like channels in the membrane. Which of the following is not true about these channels? (a) They are made primarily of α helices. (b) They are made primarily of β sheets. (c) They cannot form narrow channels. (d) They have alternating hydrophobic and hydrophilic amino acids.

(a) They are made primarily of α helices.

8-10 Which of the following statements about transcriptional regulators is false? (a) Transcriptional regulators usually interact with the sugar-phosphate backbone on the outside of the double helix to determine where to bind on the DNA helix. (b) Transcriptional regulators will form hydrogen bonds, ionic bonds, and hydrophobic interactions with DNA. (c) The DNA-binding motifs of transcriptional regulators usually bind in the major groove of the DNA helix. (d) The binding of transcriptional regulators generally does not disrupt the hydrogen bonds that hold the double helix together.

(a) Transcriptional regulators usually interact with the sugar-phosphate backbone on the outside of the double helix to determine where to bind on the DNA helix.

Which of the following changes is least likely to arise from a point mutation in a regulatory region of a gene? (a) a mutation that changes the subcellular localization of a protein (b) a mutation that changes the time in an organisms life during which a protein is expressed (c) a mutation that eliminates the production of a protein in a specific cell type (d) a mutation that increases the level of protein production in a cell

(a) a mutation that changes the subcellular localization of a protein

You discover that the underlying cause of a disease is a protein that is now less stable than the non-disease-causing version of the protein. This change is most likely due to ______________. (a) a mutation within a gene (b) a mutation within a regulatory DNA of a gene (c) gene duplication (d) horizontal gene transfer

(a) a mutation within a gene

If this hypothesis is true, which of the following types of genetic change would most likely lead to this situation? (a) a mutation within an upstream enhancer of the gene (b) a mutation within the transcription factor gene that leads to a premature stop codon after the third amino acid (c) a mutation within the transcription factor gene that leads to a substitution of a positively charged amino acid for a negatively charged amino acid\ (d) a mutation in the TATA box of the gene

(a) a mutation within an upstream enhancer of the gene

Which of the following generalities about genomes is true? (a) All vertebrate genomes contain roughly the same number of genes (b) all unicellular organisms contain the same number of genes (c) the larger the organism, the more genes it has (d) the more types of cell an organsim has the more genes it hs

(a) all verterbrate genomes contain roughly the same number of genes

8-58 MicroRNAs ____________________. (a) are produced from a precursor miRNA transcript. (b) are found only in humans. (c) control gene expression by base-pairing with DNA sequences. (d) can degrade RNAs by using their intrinsic catalytic activity

(a) are produced from a precursor miRNA transcript.

11-40 Plasma membranes are extremely thin and fragile, requiring an extensive support network of fibrous proteins. This network is called the ____________. (a) cortex. (b) attachment complex. (c) cytoskeleton. (d) spectrin.

(a) cortex.

8-56 miRNAs, tRNAs, and rRNAs all _____________. (a) do not code for proteins. (b) act in the nucleus. (c) are packaged with other proteins to form RISC. (d) form base pairs with mRNA molecules.

(a) do not code for proteins.

1-24 Membrane synthesis in the cell requires the regulation of growth for both halves of the bilayer and the selective retention of certain types of lipids on one side or the other. Which group of enzymes accomplishes both of these tasks? (a) flippases (b) phospholipases (c) convertases (d) glycosylases

(a) flippases

11-55 The endothelial cells found closest to the site of an infection express proteins called lectins. Each lectin binds to a particular ____________ that is presented on the surface of a target cell. (a) oligosaccharide (b) aminophospholipid (c) polysaccharide (d) sphingolipid

(a) oligosaccharide

11-4 Which type of lipids are the most abundant in the plasma membrane? (a) phospholipids (b) glycolipids (c) sterols (d) triacylglycerides

(a) phospholipids

11-44 The lateral movement of transmembrane proteins can be restricted by several different mechanisms. Which mechanism best describes the process by which a budding yeast cell designates the site of new bud formation during cell division? (a) proteins are tethered to the cell cortex (b) proteins are tethered to the extracellular matrix (c) proteins are tethered to the proteins on the surface of another cell (d) protein movement is limited by the presence of a diffusion barrier

(a) proteins are tethered to the cell cortex

11-18 Membrane lipids are capable of many different types of movement. Which of these does not occur spontaneously in biological membranes? (a) switching between lipid layers (b) lateral movement (c) rotation (d) flexing of hydrocarbon chains

(a) switching between lipid layers

11-1 Which of the following phenomena will be observed if a cell's membrane is pierced? (a) the membrane reseals (b) the membrane collapses (c) a tear is formed (d) the membrane expands

(a) the membrane reseals

Which of the following regions of the genome is the least likely to be conserved over evolutionary time? (a) the upstream regulatory region of a gene that encodes the region conferring tissuse specificity (b) the upstream regulatory region of a gene that binds to RNA polymerase (c) The portion of the genome that codes for protein (d) The portion of the genome that codes for RNAs that are not translated into protein

(a) the upstream regulatory region of a gene that encodes the region conferring tissue specificity

8-64 The modular nature of the Eve gene's regulatory region means that ______. (a) there are seven regulatory elements and each element is sufficient for driving expression in a single stripe. (b) all the regulatory elements for each stripe use the same transcriptional activators. (c) the E. coli LacZ gene is normally only expressed in a single stripe—unlike Eve, which is expressed in seven stripes. (d) transcription regulators only bind to the stripe 2 regulatory DNA segment in stripe 2.

(a) there are seven regulatory elements and each element is sufficient for driving expression in a single stripe.

7-67 When using a repeating trinucleotide sequence (such as 5′-AAC-3′) in a cell- free translation system, you will obtain: (a) three different types of peptides, each made up of a single amino acid (b) peptides made up of three different amino acids in random order (c) peptides made up of three different amino acids, each alternating with each other in a repetitive fashion (d) polyasparagine, as the codon for asparagine is AAC

(a) three different types of peptides, each made up of a single amino acid

11-13 Which of the following phospholipid precursors is the most hydrophobic? (a) triacylglycerol (b) diacylglycerol (c) phosphate (d) glycerol

(a) triacylglycerol

T/F: The electrochemical gradient for K+ across the plasma membrane is small. Therefore, any movement of K+ from the inside to the outside of the cell is driven solely by its concentration gradient

True

1-22 Most animal fats form a solid at room temperature, while plant fats remain liquid at room temperature. Which of the following is a feature of lipids in plant membranes that best explains this difference? (a) unsaturated hydrocarbons (b) longer hydrocarbon tails (c) higher levels of sterols (d) larger head groups

(a) unsaturated hydrocarbons

8-60 The extent of complementarity of a miRNA with its target mRNA determines ___________________________. (a) whether the mRNA will be immediately degraded or whether the mRNA will first be transported elsewhere in the cell before degradation. (b) whether the mRNA will be transported to the nucleus. (c) whether RISC is degraded. (d) whether the miRNA synthesizes a complementary strand.`

(a) whether the mRNA will be immediately degraded or whether the mRNA will first be transported elsewhere in the cell before degradation.

7-13 Which of the following molecules of RNA would you predict to be the most likely to fold into a specific structure as a result of intramolecular base-pairing? (a)5′CCCUAAAAAAAAAAAAAAAAUUUUUUUUUUUUUUUUAGGG-3′ (b)UGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUG-3′ (c) 5'-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA-3′ (d)5′GGAAAAGGAGAUGGGCAAGGGGAAAAGGAGAUGGGCAAGG-3′

(a)5′CCCUAAAAAAAAAAAAAAAAUUUUUUUUUUUUUUUUAGGG-3′

In humans and in chimps, 99% of the Alu retrotransposons are in corresponding positions. Which of the following is most likely explanation for this similarity? (a) The Alu retrotransposon is not capable of transposition in humans (b) Most of the Alu sequences in the chimps genome underwent gene duplication and divergence before humans and chimps diverged

(b)

Which of the following DNA sequences is not commonly carried on a DNA only transposon? (a) transposase gene (b) reverse transcriptase gene (c) recognition site for transposase (d) antibiotic-resistance gene

(b)

11-19 There are two properties of phospholipids that affect how tightly they pack together: the length of the hydrocarbon chain and the number of double bonds. The degree of packing, in turn, influences the relative mobility of these molecules in the membrane. Which of the following would yield the most highly mobile phospholipid (listed as number of carbons and number of double bonds, respectively)? (a) 24 carbons with 1 double bond (b) 15 carbons with 2 double bonds (c) 20 carbons with 2 double bonds (d) 16 carbons with no double bonds

(b) 15 carbons with 2 double bonds

19-21 A diploid cell containing 32 chromosomes will make a haploid cell containing ___ chromosomes. (a) 8 (b) 16 (c) 30 (d) 64

(b) 16

individual 1 is one of the parents of individual 2. The asterisk indicates the occurrence of a single mutation(in the germ line cell of zygote of individual 1).What is the chance that individual 2 will inherit the mutation in individual 1? (a) 100% (b) 50% (c) 1 in 100000 (d) none

(b) 50%

7-18 You have a piece of DNA that includes the following sequence: 5′-ATAGGCATTCGATCCGGATAGCAT-3' 3′-TATCCGTAAGCTAGGCCTATCGTA-5′ Which of the following RNA molecules could be transcribed from this piece of DNA? (a) 5′-UAUCCGUAAGCUAGGCCUAUGCUA-3′ (b) 5′-AUAGGCAUUCGAUCCGGAUAGCAU-3′ (c) 5′-UACGAUAGGCCUAGCUUACGGAUA-3′ (d) none of the above

(b) 5′-AUAGGCAUUCGAUCCGGAUAGCAU-3′

The nucleotide sequences between individuals differ by 0.1% yet the human genome is made up of about 3x10^9 nucleotide pairs. Which of the following is false? (a) In most human cells the homologous autosomes differ from each other by 0.1% (b) All changes between human individuals are single-nucleotide polymorphisms

(b) All changes between human individuals are single-nucleotide polymorphisms

Given the evolutionary relationship between higher primates shown the picture which of the following statements is false? (a) The last common ancestor of humans, chimps,gorillas and orangutans lived about 14 million years ago (b) Chimpanzees are more closely related to gorillas than humans (c) Humans and chimps diverged 6 million years ago (d) Orangutans are most divergent of the four species

(b) Chimpanzees are more closely related to gorillas than humans

7-30 Which of the following statements about RNA splicing is false? (a) Conventional introns are not found in bacterial genes. (b) For a gene to function properly, every exon must be removed from the primary transcript in the same fashion on every mRNA molecule produced from the same gene. (c) Small RNA molecules in the nucleus perform the splicing reactions necessary for the removal of introns. (d) Splicing occurs after the 5′ cap has been added to the end of the primary transcript.

(b) For a gene to function properly, every exon must be removed from the primary transcript in the same fashion on every mRNA molecule produced from the same gene.

11-38 We know the detailed molecular structure and mechanism of action of the transmembrane protein bacteriorhodopsin. This protein uses sunlight as the source of energy to pump ______ out of the cell. (a) ATP (b) H+ (c) K+ (d) Na+

(b) H+

11-34 The amino acid sequences below represent the sequences of transmembrane helices. The characteristics of α helices that form a channel are different from those that form a single transmembrane domain. Select the helix that forms a single transmembrane domain. (a) VGHSLSIFTLVISLGIFVFF (b) IMIVLVMLLNIGLAILFVHF (c) ILHFFHQYMMACNYFWMLCE (d) VTLHKNMFLTYILNSMIIII

(b) IMIVLVMLLNIGLAILFVHF

T/F: The extracellular concentration of Ca2+ is approximately 104 -fold higher than the concentration of Ca2+ in the cytosol.

True

19-3 Which of the following statements is *false*? (a) Asexual reproduction typically gives rise to offspring that are genetically identical. (b) Mutations in somatic cells are passed on to individuals of the next generation. (c) Sexual reproduction allows for a wide variety of gene combinations. (d) Gametes are specialized sex cells.

(b) Mutations in somatic cells are passed on to individuals of the next generation.

Which of the following is false about the human genome? (a) about 1.5% of the human genome codes for exons (b) Only the exons are conserved between the genomes of humans and other mammals

(b) Only the exons are conserved between the genomes of humans and other mammals

7-24 There are several reasons why the primase used to make the RNA primer for DNA replication is not suitable for gene transcription. Which of the statements below is not one of those reasons? (a) Primase initiates RNA synthesis on a single-stranded DNA template. (b) Primase can initiate RNA synthesis without the need for a base-paired primer. (c) Primase synthesizes only RNAs of about 5-20 nucleotides in length. (d) The RNA synthesized by primase remains base-paired to the DNA template.

(b) Primase can initiate RNA synthesis without the need for a base-paired primer.

11-9 A bacterium is suddenly expelled from a warm human intestine into the cold world outside. Which of the following adjustments might the bacterium make to maintain the same level of membrane fluidity? (a) Produce lipids with hydrocarbon tails that are longer and have fewer double bonds. (b) Produce lipids with hydrocarbon tails that are shorter and have more double bonds. (c) Decrease the amount of cholesterol in the membrane. (d) Decrease the amount of glycolipids in the membrane.

(b) Produce lipids with hydrocarbon tails that are shorter and have more double bonds.

7-65 You are studying a disease that is caused by a virus, but when you purify the virus particles and analyze them you find they contain no trace of DNA. Which of the following molecules are likely to contain the genetic information of the virus? (a) high-energy phosphate groups (b) RNA (c) lipids (d) carbohydrates

(b) RNA

8-62 Which (a) The RNAi mechanism is found only in plants and animals. (b) RNAi is induced when double-stranded, foreign RNA is present in the cell. (c) RISC uses the siRNA duplex to locate complementary foreign RNA molecules. (d) siRNAs bind to miRNAs to induce RNAi.

(b) RNAi is induced when double-stranded, foreign RNA is present in the cell.

7-55 Which of the following statements about prokaryotic mRNA molecules is false? (a) A single prokaryotic mRNA molecule can be translated into several proteins. (b) Ribosomes must bind to the 5′ cap before initiating translation. (c) mRNAs are not polyadenylated. (d) Ribosomes can start translating an mRNA molecule before transcription is complete.

(b) Ribosomes must bind to the 5′ cap before initiating translation.

11-59 It is possible to follow the movement of a single molecule or a small group of molecules. This requires the use of antibodies linked to small particles of gold, which appear as dark spots when tracked through video microscopy. What is this method called? What does the abbreviation stand for? (a) SDS (b) SPT (c) GFP (d) FRAP

(b) SPT

7-25 You have a bacterial strain with a mutation that removes the transcription termination signal from the Abd operon. Which of the following statements describes the most likely effect of this mutation on Abd transcription? (a) The Abd RNA will not be produced in the mutant strain. (b) The Abd RNA from the mutant strain will be longer than normal. (c) Sigma factor will not dissociate from RNA polymerase when the Abd operon is being transcribed in the mutant strain. (d) RNA polymerase will move in a backward fashion at the Abd operon in the mutant strain.

(b) The Abd RNA from the mutant strain will be longer than normal.

8-47 Which of the following statements about the Ey transcriptional regulator is false? (a) Expression of Ey in cells that normally form legs in the fly will lead to the formation of an eye in the middle of the legs. (b) The Ey transcription factor must bind to the promoter of every eye- specific gene in the fly. (c) Positive feedback loops ensure that Ey expression remains switched on in the developing eye. (d) A homolog of Ey is found in vertebrates; this homolog is also used during eye development.

(b) The Ey transcription factor must bind to the promoter of every eye- specific gene in the fly.

8-15 What do you predict would happen if you replace the Lac operator DNA from the Lac operon with the DNA from the operator region from the tryptophan operon? (a) The presence of lactose will not cause allosteric changes to the Lac repressor. (b) The Lac operon will not be transcribed when tryptophan levels are high. (c) The lack of glucose will no longer allow CAP binding to the DNA. (d) RNA polymerase will only bind to the Lac promoter when lactose is present.

(b) The Lac operon will not be transcribed when tryptophan levels are high.

11-39 In the photosynthetic archaean Halobacterium halobium, a membrane transport protein called bacteriorhodopsin captures energy from sunlight and uses it to pump protons out of the cell. The resulting proton gradient serves as an energy store that can later be tapped to generate ATP. Which statement best describes how bacteriorhodopsin operates? (a) The absorption of sunlight triggers a contraction of the β barrel that acts as the protein's central channel, squeezing a proton out of the cell. (b) The absorption of sunlight triggers a shift in the conformation of the protein's seven, membrane spanning α helices, allowing a proton to leave the cell. (c) The absorption of sunlight triggers a restructuring of bacteriorhodopsin's otherwise unstructured core to form the channel through which a proton can exit the cell. (d) The absorption of sunlight triggers the activation of an enzyme that generates ATP.

(b) The absorption of sunlight triggers a shift in the conformation of the protein's seven, membrane spanning α helices, allowing a proton to leave the cell.

8-6 Investigators performed nuclear transplant experiments to determine whether DNA is altered irreversibly during development. Which of the following statements about these experiments is true? (a) Because the donor nucleus is taken from an adult animal, the chromosomes from the nucleus must undergo recombination with the DNA in the egg for successful development to occur. (b) The embryo that develops from the nuclear transplant experiment is genetically identical to the donor of the nucleus. (c) The meiotic spindle of the egg must interact with the chromosomes of the injected nuclei for successful nuclear transplantation to occur. (d) Although nuclear transplantation has been successful in producing embryos in some mammals with the use of foster mothers, evidence of DNA alterations during differentiation has not been obtained for plants.

(b) The embryo that develops from the nuclear transplant experiment is genetically identical to the donor of the nucleus.

8-54 Which of the following statements about mRNA half-life is false? (a) The half-life of mRNAs produced from different genes will vary more than the half-life of mRNAs produced from the same gene. (b) The half-life of most eukaryotic-cell mRNAs is >24 hours. (c) The half-life of most bacterial mRNAs is shorter than the half-life of a typical eukaryotic mRNA. (d) The 5′ and 3′ untranslated regions of an mRNA often contain specific sequences that determine the lifetime of the mRNA molecule

(b) The half-life of most eukaryotic-cell mRNAs is >24 hours.

Which of the following about retroviruses is false? (a) They are packed with a few molecules of reverse t. in each virus particle (b) They use the host-genome integrase enzyme to create provirus (c) The production of viral RNAs can occur long after the initial infection of the host cell by the retrovirus (d) viral RNAs are translated by host cell ribosomes to produce the proteins required for the production of viral particles

(b) They use the host-genome integrase enzyme to create provirus

1-7 Formation of a lipid bilayer is energetically favorable. How does this arrangement result in higher entropy for the system, and thus make bilayer formation energetically favorable? (a) Polar head groups form a hydrogen-bonding network at the interface with water. (b) Water molecules form cagelike structures around hydrophobic molecules. (c) Hydrogen bonds form between neighboring polar head groups in the bilayer. (d) Fatty acid tails are highly saturated and flexible.

(b) Water molecules form cagelike structures around hydrophobic molecules.

11-27 Membrane proteins, like membrane lipids, can move laterally by exchanging positions with other membrane components. Which type of membrane proteins is expected to be the least mobile, based on their function? (a) channels (b) anchors (c) receptors (d) enzymes

(b) anchors

8-12 The tryptophan operator ___________________________. (a) is an allosteric protein. (b) binds to the tryptophan repressor when the repressor is bound to tryptophan. (c) is required for production of the mRNA encoded by the tryptophan operon. (d) is important for the production of the tryptophan repressor.

(b) binds to the tryptophan repressor when the repressor is bound to tryptophan.

8-36 How are most eukaryotic transcription regulators able to affect transcription when their binding sites are far from the promoter? (a) by binding to their binding site and sliding to the site of RNA polymerase assembly (b) by looping out the intervening DNA between their binding site and the promoter (c) by unwinding the DNA between their binding site and the promoter (d) by attracting RNA polymerase and modifying it before it can bind to the promoter

(b) by looping out the intervening DNA between their binding site and the promoter

19-28 After the first meiotic cell division ________________________. (a) two haploid gametes are produced. (b) cells are produced that contain the same number of chromosomes as somatic cells. (c) the number of chromosomes will vary depending on how the paternal and maternal chromosomes align at the metaphase plate. (d) DNA replication occurs.

(b) cells are produced that contain the same number of chromosomes as somatic cells.

8-45 Which of the following statements about iPS cells is false? (a) iPS cells are created by adding a combination of transcription regulators to a fibroblast. (b) iPS cells created from mouse cells can differentiate into almost any human cell type. (c) Stimulation by extracellular signal molecules causes iPS cells to differentiate. (d) During the de-differentiation process to become an iPS, the fibroblast will undergo changes to its gene expression profile.

(b) iPS cells created from mouse cells can differentiate into almost any human cell type.

11-15 Where does most new membrane synthesis take place in a eukaryotic cell? (a) in the Golgi apparatus (b) in the endoplasmic reticulum (c) in the plasma membrane (d) in the mitochondria (e) on ribosomes

(b) in the endoplasmic reticulum

8-43 Combinatorial control of gene expression __________________________. (a) involves every gene using a different combination of transcriptional regulators for its proper expression. (b) involves groups of transcriptional regulators working together to determine the expression of a gene. (c) involves only the use of gene activators used together to regulate genes appropriately. (d) is seen only when genes are arranged in operons.

(b) involves groups of transcriptional regulators working together to

11-45 The lateral movement of transmembrane proteins can be restricted by several different mechanisms. Which mechanism best describes the process by which focal adhesions are formed to promote cell motility? (a) proteins are tethered to the cell cortex (b) proteins are tethered to the extracellular matrix (c) proteins are tethered to the proteins on the surface of another cell (d) protein movement is limited by the presence of a diffusion barrier

(b) proteins are tethered to the extracellular matrix

7-54 In eukaryotes, but not in prokaryotes, ribosomes find the start site of translation by ____________________________. (a) binding directly to a ribosome-binding site preceding the initiation codon. (b) scanning along the mRNA from the 5′ end. (c) recognizing an AUG codon as the start of translation. (d) binding an initiator tRNA.

(b) scanning along the mRNA from the 5′ end.

11-2 The plasma membrane serves many functions, many of which depend on the presence of specialized membrane proteins. Which of the following roles of the plasma membrane could still occur if the bilayer were lacking these proteins? (a) intercellular communication (b) selective permeability (c) cellular movement (d) import/export of molecules

(b) selective permeability

8-63 The owners of a local bakery ask for your help in improving a special yeast strain they use to make bread. They would like you to help them design experiments using RNA interference to turn off genes, to allow them to test of the following statements about RNAi is true? their hypothesis that certain genes are important for the good flavors found in their bread. Of the components in the following list, which is the most important to check for in this yeast strain if you'd like this project to succeed? (a) the presence of foreign double-stranded RNA (b) the presence of genes in the genome that code for RISC proteins (c) the presence of miRNA genes in the genome (d) the presence of single-stranded siRNAs within the cell

(b) the presence of genes in the genome that code for RISC proteins

8-2 The distinct characteristics of different cell types in a multicellular organism result mainly from the differential regulation of the _________________. (a) replication of specific genes. (b) transcription of genes transcribed by RNA polymerase II. (c) transcription of housekeeping genes. (d) proteins that directly bind the TATA box of eukaryotic genes.

(b) transcription of genes transcribed by RNA polymerase II.

Which of the following statements about the globin gene family is true? (a) The globin protein which can carry oxygen molecules throughout an organisms body was first seen in ancient vertebrae species about 500 million years ago (b) The gene duplication that led to the expansions of the globin gene family led to the separation of globin (c) Some of the duplicated globin genes that arose during vertebrate evolution acquired inactivating mutations and become pseudogenes in modern vertebrates (d) As globin gene family members diverged over the course of evolution, all the DNA sequence variations that have accumulated between family members are within the regulatory DNA sequences that affect when and how strongly each globin gene is expressed.

(c)

Which of these statements is consistent with these sequence-comparison data? (a) The gorilla sequence is more similar to the chimp sequence than to the human sequence (b) since these sequences are so similar this protein must also be found in invertebrates (c) The chimp DNA sequence has likely diverged at the DNA coding for amino acid 15 from the sequence found in the last common ancestor of humans and chimps (d) The last common ancestor of chimps and gorillas most likely used AAA to code for the amino acid number 3

(c) The chimp DNA sequence has likely diverged at the DNA coding for amino acid 15 from the sequence found in the last common ancestor of humans and chimps

8-48 The MyoD transcriptional regulator is normally found in differentiating muscle cells and participates in the transcription of genes that produce muscle-specific proteins, such as those needed in contractile tissue. Amazingly, expression of MyoD in fibroblasts causes these cells derived from skin connective tissue to produce proteins normally only seen in muscles. However, some other cell types do not transcribe muscle-specific genes when MyoD is expressed in them. Which of the following statements below is the best explanation of why MyoD can cause fibroblasts to express muscle- specific genes? (a) Unlike some other cell types, fibroblasts have not lost the muscle-specific genes from their genome. (b) The muscle-specific genes must be in heterochromatin in fibroblasts. (c) During their developmental history, fibroblasts have accumulated some transcriptional regulators in common with differentiating muscle cells. (d) The presence of MyoD is sufficient to activate the transcription of muscle- specific genes in all cell types.

(c) During their developmental history, fibroblasts have accumulated some transcriptional regulators in common with differentiating muscle cells.

8-40 Which of the following statements about nucleosomes is true? (a) Nucleosomes activate transcription when bound to the promoter. (b) Although RNA polymerase can access DNA packed within nucleosomes, the general transcription factors and transcriptional regulators cannot. (c) Histone acetyltransferases affect transcription by both altering chromatin structure to allow accessibility to the DNA and by adding acetyl groups to histones that can bind proteins that promote transcription. (d) Histone deacetylases remove lysines from histone tails.

(c) Histone acetyltransferases affect transcription by both altering chromatin structure to allow accessibility to the DNA and by adding acetyl groups to histones that can bind proteins that promote transcription.

8-57 Which of the following is not involved in post-transcriptional control? (a) the spliceosome (b) Dicer (c) Mediator (d) RISC

11-8 Which of the following statements is true? (a) Phospholipids will spontaneously form liposomes in nonpolar solvents. (b) In eukaryotes, all membrane-enclosed organelles are surrounded by one lipid bilayer. (c) Membrane lipids diffuse within the plane of the membrane. (d) Membrane lipids frequently flip-flop between one monolayer and the other.

7-61 Which of the following statements about the proteasome is false? (a) Ubiquitin is a small protein that is covalently attached to proteins to mark them for delivery to the proteasome. (b) Proteases reside in the central cylinder of a proteasome. (c) Misfolded proteins are delivered to the proteasome, where they are sequestered from the cytoplasm and can attempt to refold. (d) The protein stoppers that surround the central cylinder of the proteasome use the energy from ATP hydrolysis to move proteins into the proteasome inner chamber;

(c) Misfolded proteins are delivered to the proteasome, where they are sequestered from the cytoplasm and can attempt to refold.

7-62 Which of the following molecules is thought to have arisen first during evolution? (a) protein (b) DNA (c) RNA (d) all came to be at the same time

Which protein is not encoded in the HIV genome? (a) reverse transcriptase (b) envelope protein (c) RNA polymerase (d) capsid protein

7-64 Ribozymes catalyze which of the following reactions? (a) DNA synthesis (b) transcription (c) RNA splicing (d) protein hydrolysis

Given this information, which of the following is false? (a) These are all highly related species because the sequence divergence between the most divergent species is 3% (b) Species M is just as related to species G as it is to species J (c) Species N is more closely related to the last common ancestor of all these species than to any of the other species shown in the diagram (d) Species G and H are as closely relateed to each other as species J and K are to each other

(c) Species N is more closely related to the last common ancestor of all these species than to any of species in the diagram

7-50 The ribosome is important for catalyzing the formation of peptide bonds. Which of the following statements is true? (a) The number of rRNA molecules that make up a ribosome greatly exceeds the number of protein molecules found in the ribosome. (b) The large subunit of the ribosome is important for binding to the mRNA. (c) The catalytic site for peptide bond formation is formed primarily from an rRNA. (d) Once the large and small subunits of the ribosome assemble, they will not separate from each other until degraded by the proteasome.

T/F: The intermembrane space of the mitochondria is chemically equivalent to the cytosol with respect to pH and the small molecules present.

True

7-14 Which one of the following is the main reason that a typical eukaryotic gene is able to respond to a far greater variety of regulatory signals than a typical prokaryotic gene or operon? (a) Eukaryotes have three types of RNA polymerase. (b) Eukaryotic RNA polymerases require general transcription factors. (c) The transcription of a eukaryotic gene can be influenced by proteins that bind far from the promoter. (d) Prokaryotic genes are packaged into nucleosomes.

What is the most likely explanation of why the overall mutation rates in bacteria and in humans are roughly similar? (a) Cell division needs to be fast (b) Most mutations are silent (c) There is a narrow range of mutation rates that offers an optimal balance between keeping the genome stable and generating sufficient diversity in a population (d) It benefits multicellular organisms to have some variability among its cells

(c) There is a narrow range of mutation rates that offers an optimal balance between keeping the genome stable and generating sufficient diversity in a population

11-54 Both glycoproteins and proteoglycans contribute to the carbohydrate layer on the surface of the cell. Which of the following is not true of glycoproteins? (a) They can be secreted into the extracellular environment. (b) They have only one transmembrane domain. (c) They have long carbohydrate chains. (d) They are recognized by lectins.

8-46 Which of the following statements about how fruit flies can develop an eye in the middle of a leg is true? (a) When the Ey gene is expressed in adult leg cells, these cells de- differentiate and become eye cells. (b) The Ey gene encodes a transcription regulator that is the only transcription regulator used to produce a fruit-fly eye. (c) When the Ey gene is introduced into cells that would normally give rise to a leg, the transcription regulators used to control its expression in the leg are different from those that are normally used to control Ey expression in the eye. (d) All the eye cells found in the adult leg are a single cell type and have identical characteristics.

(c) When the Ey gene is introduced into cells that would normally give rise to a leg, the transcription regulators used to control its expression in the leg are different from those that are normally used to control Ey expression in the eye.

19-62 Finding co-inheritance of a SNP variant and a disease tells scientists that ____________________. (a) everybody who carries this SNP will get the disease. (b) sequences within the SNP cause the disease. (c) a gene important for causing the disease is linked to the SNP. (d) SNPs on other chromosomes will not be co-inherited with the disease.

8-3 The human genome encodes about 21,000 protein-coding genes. Approximately how many such genes does the typical differentiated human cell express at any one time? (a) 21,000—all of them (b) between 18,900 and 21,000—at least 90% of the genes (c) between 5000 and 15,000 (d) less than 2100

8-11 Operons ___________________________. (a) are commonly found in eukaryotic cells. (b) are transcribed by RNA polymerase II. (c) contain a cluster of genes transcribed as a single mRNA. (d) can only be regulated by gene activator proteins.

11-35 Unlike soluble, cytosolic proteins, membrane proteins are more difficult to purify. Which of the following substances is most commonly used to help purify a membrane protein? (a) high salt solution (b) sucrose (c) detergent (d) ethanol

7-4 RNA in cells differs from DNA in that ___________________. (a) it contains the base uracil, which pairs with cytosine. (b) it is single-stranded and cannot form base pairs. (c) it is single-stranded and can fold up into a variety of structures. (d) the sugar ribose contains fewer oxygen atoms than does deoxyribose.

8-61 Which (a) One miRNA can regulate the expression of many genes. (b) miRNAs are transcribed in the nucleus from genomic DNA. (c) miRNAs are produced from rRNAs. (d) miRNAs are made by RNA polymerase. of the following statements about miRNAs is false

Alternative exons can arise through the duplication and divergence of existing exons. What type of mutation below would be least tolerated during the evolution of a new exon? (a) a nucleotide change of A to G (b) a deletion of three consective bases (c) mutation of the first nucleotide in the intron

11-21 Cholesterol serves several essential functions in mammalian cells. Which of the following is not influenced by cholesterol? (a) membrane permeability (b) membrane fluidity (c) membrane rigidity (d) membrane thickness

(d) membrane thickness

11-46 The lateral movement of transmembrane proteins can be restricted by several different mechanisms. Which mechanism best describes the process by which neutrophils are recruited by endothelial cells? (a) proteins are tethered to the cell cortex (b) proteins are tethered to the extracellular matrix (c) proteins are tethered to the proteins on the surface of another cell (d) protein movement is limited by the presence of a diffusion barrier

11-48 The lateral movement of transmembrane proteins can be restricted by several different mechanisms. Which mechanism best describes the process by which an antigen-presenting cell triggers an adaptive immune response? (a) proteins are tethered to the cell cortex (b) proteins are tethered to the extracellular matrix (c) proteins are tethered to the proteins on the surface of another cell (d) protein movement is limited by the presence of a diffusion barrier

7-51 Which of the following statements is true? (a) Ribosomes are large RNA structures composed solely of rRNA. (b) Ribosomes are synthesized entirely in the cytoplasm. (c) rRNA contains the catalytic activity that joins amino acids together. (d) A ribosome binds one tRNA at a time.

7-22 The sigma subunit of bacterial RNA polymerase ___________________. (a) contains the catalytic activity of the polymerase. (b) remains part of the polymerase throughout transcription. (c) recognizes promoter sites in the DNA. (d) recognizes transcription termination sites in the DNA.

Which species would be best to examine to determine what the sequence was in the last common ancestor of species X and S. cerevisiae? (a) Species V (b) species W (c) species Y (d) species Z

8-1 A neuron and a white blood cell have very different functions. For example, a neuron can receive and respond to electrical signals while a white blood cell defends the body against infection. This is because ______. (a) the proteins found in a neuron are completely different from the proteins found in a white blood cell. (b) the neuron and the white blood cell within an individual have the same genome. (c) the neuron expresses some mRNAs that the white blood cell does not. (d) neurons and white blood cells are differentiated cells and thus no longer need to transcribe and translate genes.

8-41 In principle, how many different cell types can an organism having four different types of transcription regulator and thousands of genes create? (a) up to 4 (b) up to 8 (c) up to 16 (d) thousands

Given this information which of the following statements is true? (a) The ancestral globin gene arose 500 million years ago (b) the a-globin gene is more closely related to the e-globin gene than to the s-globin gene (c) The nucleotide sequences of the two y-globins will be most similar because they are closest together on the chromosome (d) The fetal B-globins arose from a gene duplication that occured 200 million years ago which gave rise to a B globin expressed in the fetus and a B globin expressed in the adult

(d)

Viral genomes _________________. (a) can be made of DNA (b) can be made of RNA (c) can be either double stranded or single (d) all of the above

(d)

There is an experiment used to determine the spontaneous mutation rate in E. coli. If the spontaneous mutation rate in E. coli is 1 mistake in every 10^9nucleotides copied, about how many colonies would you expect to see on the plates lacking histidine if you were to assay 10^11 cells from the culture for their ability to form colonies? (a) 1 (b) 2 (c) 10 (d) 100

(d) 100

Which of the following statements is false? (a) Nucleotides and amino acids can act as extracellular signal molecules. (b) Some signal molecules can bind directly to intracellular proteins that bind DNA and regulate gene transcription. (c) Some signal molecules are transmembrane proteins. (d) Dissolved gases such as nitric oxide (NO) can act as signal molecules, but because they cannot interact with proteins they must act by affecting membrane lipids.

(d) Dissolved gases such as nitric oxide (NO) can act as signal molecules, but because they cannot interact with proteins they must act by affecting membrane lipids.

**There is an experiment used to determine the spontaneous mutation rate in E. coli. If the spontaneous mutation rate in E. coli is 1 mistake in every 10^9 nucleotides copied, about how many colonies would you expect to see on the plates lacking histidine if you were to assay 10^11 cells from the culture for their ability to form colonies? (a) 1 (b) 2 (c) 10 (d) 100

Which of the following about mobile genetic elements is true? (a) DNA-only transporons do not code for proteins but instread rely on transposases found in the cells that are infected by viruses (b) The two major families pf transposable sequences found in the human genome are DNA only transposons that move by replicative transoposition (d) During cut-and-paste transposition, the donor DNA will no longer have the mobile genetic element embedded in its sequence when transposition is complete

(d) During cut-and-past transpositon, the donor DNA will no longer have the mobile genetic element embedded in its sequence when transposition is complete

Which of the following is false? (a) The human genome is more similar to the orangutan genome than it is to the mouse genome (b) A comparison of genomes shows that 90% of the human genome shares regions of conserved synteny with the mouse genome (c) Primates, dogs, mice and chickens all have the same number of genes (d) Genes that code for ribosomal RNA share significant similarity in all eukaryotes except are much more difficult to recognize in archaea

(d) Genes that code for ribosomal RNA share significant similarity in all eukaryotes except are much more difficult to recognize in archaea

8-52 Which of the following statements about DNA methylation in eukaryotes is false? (a) Appropriate inheritance of DNA methylation patterns involves maintenance methyltransferase. (b) DNA methylation involves a covalent modification of cytosine bases. (c) Methylation of DNA attracts proteins that block gene expression. (d) Immediately after DNA replication, each daughter helix contains one methylated DNA strand, which corresponds to the newly synthesized strand.

(d) Immediately after DNA replication, each daughter helix contains one methylated DNA strand, which corresponds to the newly synthesized strand.

7-12 Unlike DNA, which typically forms a helical structure, different molecules of RNA can fold into a variety of three-dimensional shapes. This is largely because ___________________. (a) RNA contains uracil and uses ribose as the sugar. (b) RNA bases cannot form hydrogen bonds with each other. (c) RNA nucleotides use a different chemical linkage between nucleotides compared to DNA. (d) RNA is single-stranded.

(d) RNA is single-stranded.

Which of the following do you not expect to find in the set of genes found in all organisms on Earth? (a) DNA replication (b) DNA repair (c) protein production (d) RNA splicing

(d) RNA splicing

8-5 Which of the following statements about differentiated cells is true? (a) Cells of distinct types express nonoverlapping sets of transcription factors. (b) Once a cell has differentiated, it can no longer change its gene expression. (c) Once a cell has differentiated, it will no longer need to transcribe RNA. (d) Some of the proteins found in differentiated cells are found in all cells of a multicellular organism.

(d) Some of the proteins found in differentiated cells are found in all cells of a multicellular organism.

Which of the following statements of pseudogenes is false? (a) they code for microRNAs (b) They share significant nucleotide similarity with functional genes (c) They are no longer expressed in the cell (d) There are estimated to be around 20,000 in the human genome

(d) There are estimated to be around 20,000 pseudogenes in the human genome

7-63 According to current thinking, the minimum requirement for life to have originated on Earth was the formation of a _______________. (a) molecule that could provide a template for the production of a complementary molecule. (b) double-stranded DNA helix. (c) molecule that could direct protein synthesis. (d) molecule that could catalyze its own replication.

(d) molecule that could catalyze its own replication.

T/F: The iron-sulfur centers in NADH dehydrogenase are relatively poor electron acceptors.

True

7-23 Which of the following might decrease the transcription of only one specific gene in a bacterial cell? (a) a decrease in the amount of sigma factor (b) a decrease in the amount of RNA polymerase (c) a mutation that introduced a stop codon into the DNA that precedes the gene's coding sequence (d) a mutation that introduced extensive sequence changes into the DNA that precedes the gene's transcription start site

(d) a mutation that introduced extensive sequence changes into the DNA that precedes the gene's transcription start site

1-51 Diversity among the oligosaccharide chains found in the carbohydrate coating of the cell surface can be achieved in which of the following ways? (a) varying the types of sugar monomers used (b) varying the types of linkages between sugars (c) varying the number of branches in the chain (d) all of the above

(d) all of the above

19-53 Loss-of-function mutations ________________________. (a) cause the production of proteins that are active in inappropriate circumstances. (b) will usually show a phenotype when heterozygous. (c) are only present in a population at barely detectable levels. (d) are usually recessive.

(d) are usually recessive.

7-34 snRNAs ___________________. (a) are translated into snRNPs. (b) are important for producing mature mRNA transcripts in bacteria. (c) are removed by the spliceosome during RNA splicing. (d) can bind to specific sequences at intron-exon boundaries through complementary base-pairing.

(d) can bind to specific sequences at intron-exon boundaries through complementary base-pairing.

11-6 Which of the following membrane lipids does not contain a fatty acid tail? (a) phosphatidylcholine (b) a glycolipid (c) phosphatidylserine (d) cholesterol

(d) cholesterol

11-12 Some lipases are able to cleave the covalent bonds between the glycerol backbone and the attached fatty acid. What final products do you expect to accumulate through the action of the enzyme monoacylglycerol lipase? (a) phosphoglycerol and free fatty acid (b) sterol and glycerol (c) free phosphate and glycerol (d) glycerol and free fatty acid

(d) glycerol and free fatty acid

8-4 Which of the following is not a good example of a housekeeping protein? (a) DNA repair enzymes (b) histones (c) A TP synthase (d) hemoglobin

(d) hemoglobin

This newly discovered antibiotic resistance in E Coli is most likely due to ____________. (a) a mutation within a gene (b) a mutation within the regulatory DNA of a gene (c) gene duplication (d) horizontal gene transfer

(d) horizontal gene transfer

Which of the following would contribute most to successful exon shuffling? (a) shorter introns (b) a haploid genome (c) exons that code for more than one protein domain (d) introns that contain regions of similarity to one another

(d) introns that contain regions of similarity to one another

7-28 Total nucleic acids are extracted from a culture of yeast cells and are then mixed with resin beads to which the polynucleotide 5 - TTTTTTTTTTTTTTTTTTTTTTTTT-3 has been covalently attached. After a short incubation, the beads are then extracted from the mixture. When you analyze the cellular nucleic acids that have stuck to the beads, which of the following is most abundant? (a) DNA (b) tRNA (c) rRNA (d) mRNA

(d) mRNA

7-5 Transcription is similar to DNA replication in that ___________________. (a) an RNA transcript is synthesized discontinuously and the pieces are then joined together. (b) it uses the same enzyme as that used to synthesize RNA primers during DNA replication. (c) the newly synthesized RNA remains paired to the template DNA. (d) nucleotide polymerization occurs only in the 5′-to-3′ direction.

(d) nucleotide polymerization occurs only in the 5′-to-3′ direction.

8-51 Which of the following is not a general mechanism that cells use to maintain stable patterns of gene expression as cells divide? (a) a positive feedback loop, mediated by a transcriptional regulator that activates transcription of its own gene in addition to other cell-type- specific genes (b) faithful propagation of condensed chromatin structures as cells divide (c) inheritance of DNA methylation patterns when cells divide (d) proper segregation of housekeeping proteins when cells divide

(d) proper segregation of housekeeping proteins when cells divide

11-47 The lateral movement of transmembrane proteins can be restricted by several different mechanisms. Which mechanism best describes the process by which nutrients are taken up at the apical surface of the epithelial cells that line the gut and released from their basal and lateral surfaces? (a) proteins are tethered to the cell cortex (b) proteins are tethered to the extracellular matrix (c) proteins are tethered to the proteins on the surface of another cell (d) protein movement is limited by the presence of a diffusion barrier

(d) protein movement is limited by the presence of a diffusion barrier

11-25 Membrane curvature is influenced by the differential lipid composition of the two membrane monolayers. Which factor do you think has the largest impact on the curvature of biological membranes? (a) amount of cholesterol (b) charge of the lipid head group (c) length of the hydrocarbon tails (d) size of the lipid head group

(d) size of the lipid head group

11-41 Red blood cells have been very useful in the study of membranes and the protein components that provide structural support. Which of the following proteins is the principal fibrous protein in the cortex of the red blood cell? (a) tubulin (b) attachment proteins (c) actin (d) spectrin

(d) spectrin

8-55 Using genetic engineering techniques, you remove the sequences that code for the ribosome-binding sequences of the bacterial LacZ gene. The removal of these sequences will lead to ___________. (a) more LacZ protein produced due to faster ribosome movement across the LacZ mRNA. (b) transcriptional repression, resulting in fewer mRNA molecules produced from this gene. (c) a longer half-life for the LacZ mRNA. (d) translational inhibition of the LacZ mRNA.

(d) translational inhibition of the LacZ mRNA.

19-1 Organisms that reproduce sexually ________________________. (a) must be haploid, unlike organisms that reproduce asexually. (b) can reproduce only with a partner that carries the same alleles. (c) create zygotes that are genetically identical to each other. (d) undergo a sexual reproductive cycle that involves an alternation of haploid cells with the generation of diploid cells.

(d) undergo a sexual reproductive cycle that involves an alternation of haploid cells with the generation of diploid cells.

**HIV is a human retrovirus that integrates into the host cell's genome and will eventually replicate, produce viral proteins, and ultimately escape from the host cell. Which of the following proteins is not encoded in the HIV genome? (a) reverse transcriptase (b) envelope protein (c) RNA polymerase (d) capsid protein

1. A 2. D 3. B 4. E 5. A 6. C

**Match the type of phenotypic change below with the type of genetic change most likely to cause it. Each type of genetic change may be used more than once, or may not be used at all. Phenotypic changes: 1. A protein normally localized in the nucleus is now localized in the cytoplasm. _________ 2. A protein acquires a DNA-binding domain. _________ 3. Tandem copies of a gene are found in the genome. _________ 4. A copy of a bacterial gene is now found integrated on a human chromosome. _________ 5. A protein becomes much more unstable. _________ 6. A protein normally expressed only in the liver is now expressed in blood cells. ________ Types of genetic change: A. mutation within a gene B. gene duplication C. mutation in a regulatory region D. exon shuffling E. horizontal gene transfer

A. sugar metabolism B. DNA replication C. lipid synthesis

**Some types of gene are more highly conserved than others. For each of the following pairs of gene functions, choose the one that is more likely to be highly conserved. A. genes involved in sexual reproduction / genes involved in sugar metabolism B. DNA replication / developmental pathways C. hormone production / lipid synthesis

**The nucleotide sequences between individuals differ by 0.1%, yet the human genome is made up of about 3 × 109 nucleotide pairs. Which of the following statements is false? (a) In most human cells, the homologous autosomes differ from each other by 0.1%. (b) All changes between human individuals are single-nucleotide polymorphisms. (c) Any two individuals (other than identical twins) will generally have more than 3 million genetic differences in their genomes. (d) Much of the variation between human individuals was present 100,000 years ago, when the human population was small.

**The yeast genome was sequenced more than 15 years ago, yet the total number of genes continues to be refined. The sequencing of closely related yeast species was important for validating the identity of short (less than 100 nucleotides long) open reading frames (ORFs) that were otherwise difficult to predict. What is the main reason that these short ORFs are hard to find without the genomes of other yeast for comparison? (a) Short ORFs are found only in yeast. (b) The short ORFs code for RNAs. (c) Many short stretches of DNA may lack a stop codon simply by chance, making it difficult to distinguish those DNA sequences that code for proteins from those that do not. (d) Short ORFs occur mainly in gene-rich regions, making them difficult to identify by computer programs

T/F: The proteins of the electron-transport chain remove a pair of high-energy electrons from the cofactors NADH and FADH2, after which the electrons move across the inner mitochondrial membrane to maintain the voltage gradient.

False

**Which of the following changes is least likely to arise from a point mutation in a regulatory region of a gene? (a) a mutation that changes the time in an organism's life during which a protein is expressed (b) a mutation that eliminates the production of a protein in a specific cell type (c) a mutation that changes the subcellular localization of a protein (d) a mutation that increases the level of protein production in a cell

**Which of the following generalities about genomes is true? (a) All vertebrate genomes contain roughly the same number of genes. (b) All unicellular organisms contain roughly the same number of genes. (c) The larger an organism, the more genes it has. (d) The more types of cell an organism has, the more genes it has.

**Which of the following statements about retroviruses is false? (a) Retroviruses are packaged with a few molecules of reverse transcriptase in each virus particle. (b) Retroviruses use the host-genome integrase enzyme to create the provirus. (c) The production of viral RNAs can occur long after the initial infection of the host cell by the retrovirus. (d) Viral RNAs are translated by host-cell ribosomes to produce the proteins required for the production of viral particles.

**Which of the following statements is false? (a) The human genome is more similar to the orangutan genome than it is to the mouse genome. (b) A comparison of genomes shows that 90% of the human genome shares regions of conserved synteny with the mouse genome. (c) Primates, dogs, mice, and chickens all have about the same number of genes. (d) Genes that code for ribosomal RNA share significant similarity in all eukaryotes but are much more difficult to recognize in archaea.

**Which of the following statements is true? (a) The intron structure of most genes is conserved among vertebrates. (b) The more nucleotides there are in an organism's genome, the more genes there will be in its genome. (c) Because the fly Drosophila melanogaster and humans diverged from a common ancestor so long ago, a gene in the fly will show more similarity to another gene from the same species than it will to a human gene. (d) An organism from the same Order as another will be more likely to have a genome of the same size than will a more evolutionarily diverged animal.

**Which of the following would contribute most to successful exon shuffling? (a) shorter introns (b) a haploid genome (c) exons that code for more than one protein domain (d) introns that contain regions of similarity to one another

**Your friend works in a lab that is studying why a particular mutant strain of Drosophila grows an eye on its wing. Your friend discovers that this mutant strain of Drosophila is expressing a transcription factor incorrectly. In the mutant Drosophila, this transcription factor, which is normally expressed in the primordial eye tissue, is now misexpressed in the primordial wing tissue, thus turning on transcription of the set of genes required to produce an eye in the wing primordial tissue. If this hypothesis is true, which of the following types of genetic change would most likely lead to this situation? (a) a mutation within the transcription factor gene that leads to a premature stop codon after the third amino acid (b) a mutation within the transcription factor gene that leads to a substitution of a positively charged amino acid for a negatively charged amino acid (c) a mutation within an upstream enhancer of the gene (d) a mutation in the TATA box of the gene

Match the target of the G protein with the appropriate signaling outcome. adenylyl cyclase ____1____ ion channels ____2_____ phospholipase C ____3_____ A. cleavage of inositol phospholipids B. increase in cAMP levels C. changes in membrane potential

1) B 2) C 3) A

The following proteins are important for cell movement. Match the following proteins with their function. myosin II ___1______ ARP proteins _____2___ profilin ____3_____ integrins ____4_____ A. nucleation of new actin filaments B. regulation of the availability of actin monomers C. involvement in focal contacts D. contracting the rear of the cell

1) D 2) A 3) B 4) C

Name the three main classes of cell-surface receptor.

1. ion-channel-linked receptors 2. G-protein linked receptors 3. enzyme-linked receptors

How many years ago did species M and N diverge from their last common ancestor?

10 million years ago

How many different splice isoforms could be produced for this gene?

120

Consider an animal cell that has eight chromosomes (four pairs of homologous chromosomes) in G1 phase. How many of each of the following structures will the cell have at mitotic prophase? A. Centromeres

19-10 Why is sexual reproduction more beneficial to a species living in an unpredictable environment than to one living in a constant environment?

19-10 The real benefit in sexual reproduction seems to be that parents produce children that are genetically unlike either parent and that are not genetically identical to each other. Sexual reproduction provides more variation in the population than asexual reproduction could provide, and is an advantage if the environment is variable, because any one combination of the parents' characteristics, however well adapted to the prevailing conditions, may or may not be the best in a new situation.

Mitogens are _____. (a) extracellular signals that stimulate cell division. (b) transcription factors important for cyclin production. (c) kinases that cause cells to grow in size. (d) produced by mitotic cells to keep nearby neighboring cells from dividing.

19-11 Is the following statement true or false? Explain. Somatic cells leave no progeny and thus, in an evolutionary sense, exist only to help create, sustain, and propagate the germ cells.

19-11 *True*. Only germ cells contribute genetic material to the next generation of organisms, and thus only germ cells leave an evolutionary legacy in the gene pool of the species. The only contribution of somatic cells to subsequent generations arises through the assistance they provide to dissemination of the genetic material in the germ cells. In accordance with this, mutations that arise in somatic cells are not passed along to offspring.

19-12 Sexual reproduction is a large drain on the limited resources of an individual. Nonetheless, sexual reproduction is common. In fact, to allow sexual reproduction, organisms have evolved many elaborate anatomical structures, cellular processes, and chemical signals. For example, flowers exist entirely to further the goal of sexual reproduction, and many plants have enlisted the help of bees and birds to aid in the dissemination of their germ cells. Describe one reason why most multicellular organisms have evolved to reproduce sexually instead of relying solely on asexual reproduction.

19-12 A definitive explanation of the evolutionary advantages of sexual reproduction over asexual reproduction is elusive, but several benefits seem clear. ---1. The reshuffling of genes that occurs during sexual reproduction generates most of the diversity between organisms within a species. Having a large variety of different genetic combinations in a population may help guarantee that at least a few individuals will survive after a sudden and unpredictable change in the environment. This is why some ecologists are concerned about the global trend toward monoculture, namely limiting cultivation to only a small number of varieties of each species of plant, each variety being inbred and genetically uniform. ---2. The competition between males for the available females may increase the frequency of advantageous alleles in the gene pool while efficiently eliminating deleterious combinations of alleles. This is because, in many species, only the strongest and healthiest males succeed in mating, whereas other males, carrying less successful combinations of alleles, leave no progeny. ---3. Sexual reproduction may help to eliminate deleterious recessive genes from a population in another way also: a recessive deleterious mutation in a gene may be "unmasked" in a haploid germ cell because, in contrast with a heterozygous diploid cell, the haploid cell carrying the mutation contains no normal allele to provide the gene function. Because there is competition between germ cells for fertilizing partner cells, gametes with recessive deleterious mutations are less likely to form zygotes.

19-13 Indicate whether each of the following is true for meiosis, mitosis, both, or neither. A. formation of a bivalent B. genetically identical products C. condensation of chromosomes D. segregation of all paternal chromosomes to one cell E. involvement of DNA replication

19-13 A. formation of a bivalent - *meiosis* B. genetically identical products - *mitosis* C. condensation of chromosomes - *both* D. segregation of all paternal chromosomes to one cell - *neither* E. involvement of DNA replication - *both*

19-14 The formation of a bivalent during meiosis ensures that _______. (a) one chromatid from the mother and one chromatid from the father will segregate together during meiosis I. (b) all four sister chromatids remain together until the cell is ready to divide. (c) recombination will occur between identical sister chromatids. (d) the sex chromosomes, which are not identical, will line up separately at the metaphase plate during meiosis I.

19-14 Choice (b) is correct. Both chromatids from a single parent will segregate together during meiosis I [choice (a)]. Recombination occurs between nonidentical sister chromatids [choice (c)]. The sex chromosomes will come together to form a bivalent, despite not being identical [choice (d)].

19-15 Imagine meiosis in a diploid organism that only has a single chromosome. Like most diploid organisms, it received one copy of this chromosome from each of its parents and the two homologs are genetically distinct. If only a single homologous recombination event occurs during meiosis, which of the following choices below correctly describes the four gametes formed. (a) None of the gametes will contain chromosomes identical to the chromosomes found in the original diploid cell. (b) All four of the gametes will have chromosomes identical to the chromosomes found in the original diploid cell. (c) Three of the gametes will have chromosomes identical to the chromosomes found in the original diploid cell, while one of the gametes will have chromosomes that are different. (d) Two of the gametes will have chromosomes identical to the chromosomes found in the original diploid cell, while two of the gametes will have chromosomes that are different.

19-15 (d) A single recombination event will lead to an exchange of genetic information between two of the chromatids—one from each parent

19-16 There are organisms that go through meiosis but do not undergo recombination when forming haploid gametes. Which of the following statements correctly describes the gametes produced by such an organism. (Assume that these organisms are diploid, that each of the two homologous chromosomes are genetically distinct as typically found in the wild, and that these organisms have more than one chromosome.) (a) All gametes formed during a single meiosis will be identical. (b) Due to the random assortment of homologs, each of the gametes formed during a single meiosis will be different. (c) This organism could potentially produce 2n genetically distinct gametes, where n is its haploid number of chromosomes. (d) The fusion of any two gametes produced by such an organism that does not undergo recombination during meiosis will create a cell that is genetically identical to that individual.

19-16 Choice (c) is correct. Although it is true that the homologs will randomly assort in meiosis I [choice (b)], this will only create two different types of genetic combinations in a single meiosis. Thus, four gametes will be produced, and the two products of meiosis II meiosis will be genetically identical to each other. Because the two homologous chromosomes are genetically distinct, the four gametes formed during meiosis cannot be identical [choice (a)]. Because the two homologs are genetically distinct and segregate randomly in meiosis I, the fusion of any two gametes produced by an individual will lead to unique combinations of maternal and paternal chromosomes, and thus the resulting cell will not be genetically identical to the individual [choice (d)].

19-17 Meiosis is a highly specialized cell division in which several events occur in a precisely defined order. Please order the meiotic events listed below. 1. loss of cohesins near centromeres 2. chromatid pairing 3. chromosome condensation 4. chromosome replication 5. degradation of cohesins bound to chromosome arms 6. formation of chiasmata (chiasmata = plural of chiasma) 7. homolog pairing 8. alignment of chromosomes at the metaphase plate

19-17 4, 2, 7, 6, 3, 8, 5, 1. *chromosome replication *chromatid pairing *homolog pairing *formation of chiasmata (chiasmata = plural of chiasma) *chromosome condensation *alignment of chromosomes at the metaphase plate *degradation of cohesins bound to chromosome arms *loss of cohesins near centromeres Chromosome replication (4) occurs during meiotic S phase, and immediately after replication the resultant sister chromatids are paired tightly by cohesins (2). During meiotic G2, or prophase, the two homologous chromosomes pair (7) and undergo recombination to produce reciprocal exchanges of genetic material that are visible as chiasmata (6). Meiotic division I begins with chromosome condensation (3) and proceeds to metaphase, when chromosomes align at a central plate (8). Anaphase of meiotic division I is triggered by loss of the cohesin glue on the chromosome arms (5), which allows the homologs to be segregated. Anaphase of meiotic division II is triggered by degradation of cohesins near the centromere (1), which allows sister chromatids to be segregated.

19-20 Which of the following statements most correctly describes meiosis? (a) Meiosis involves two rounds of DNA replication followed by a single cell division. (b) Meiosis involves a single round of DNA replication followed by four successive cell divisions. (c) Meiosis involves four rounds of DNA replication followed by two successive cell divisions. (d) Meiosis involves a single round of DNA replication followed by two successive cell divisions.

19-20 (d) Meiosis involves a single round of DNA replication followed by two successive cell divisions.

19-18 For each of the following sentences, choose one of the options enclosed in square brackets to make a correct statement. Starting with a single diploid cell, mitosis produces *[two/four]* *[identical/different]* *[haploid/diploid]* cells, whereas meiosis yields *[two/four]* *[identical/different]* *[haploid/diploid]* cells. This is accomplished in meiosis because a single round of chromosome *[replication/segregation]* is followed by two sequential rounds of *[replication/segregation]*. Mitosis is more like meiosis *[I/II]* than meiosis *[I/II]*. In meiosis I, the kinetochores on sister chromatids behave *[independently/coordinately]* and thus attach to microtubules from the *[same/opposite]* spindle. The cohesin-mediated glue between *[chromatids/homologs]* is regulated differently near the centromeres than along the chromosome arms. Cohesion is lost first at the *[centromeres/arms]* to allow segregation of *[chromatids/homologs]* and is lost later at the *[centromeres/arms]* to trigger segregation of *[chromatids/homologs]*.

19-18 Starting with a single diploid cell, mitosis produces *two* *identical* *diploid* cells, whereas meiosis yields *four* *different* *haploid* cells. This is accomplished in meiosis because a single round of chromosome *replication* is followed by two sequential rounds of *segregation*. Mitosis is more like meiosis *II* than meiosis *I*. In meiosis I, the kinetochores on sister chromatids behave *coordinately* and thus attach to microtubules from the *same* spindle. The cohesin-mediated glue between *chromatids* is regulated differently near the centromeres than along the chromosome *arms*. Cohesion is lost first at the arms to allow segregation of *homologs* and is lost later at the *centromeres* to trigger segregation of *chromatids*.

19-19 In the absence of recombination, how many genetically different types of gamete can an organism with five homologous chromosome pairs produce? (a) 5 (b) 10 (c) 32 (d) 64

19-19 (c) Because homologous chromosomes assort randomly at meiosis and a gamete has two choices for each chromosome (because sexual organisms are diploid), there are 25, or 32, possible genetically different gametes.

19-2 Which of the following statements is *true*? (a) Another name for the fertilized egg cell is the zygote. (b) Diploid organisms reproduce only sexually. (c) All sexually reproducing organisms must have two copies of every chromosome. (d) Gametes have only one chromosome.

19-2 Choice (a) is correct. Some diploid organisms (for example, many plants) are capable of asexual reproduction [choice (b)]. Many organisms have sex chromosomes that are only present in one copy in the diploid organism [choice (c)]. Gametes have only one member of each pair of homologous chromosomes, but because most organisms have more than one pair of homologous chromosomes, most gametes have more than one chromosome [choice (d)].

19-22 Imagine a diploid sexually reproducing organism, Diploidus sexualis, that contains three pairs of chromosomes. This organism is unusual in that no recombination between homologous chromosomes occurs during meiosis. A. Assuming that the chromosomes are distributed independently during meiosis, how many different types of sperm or egg cells can a single individual of this species produce? B. What is the likelihood that two siblings of this species will be genetically identical? You can assume that the homologous chromosomes of each parent are different from one another and from their counterparts in the other parent.

19-22 A. Eight different types. With respect to each of the three chromosomes, an individual can produce two kinds of gamete. The gamete can receive the copy that the individual received from "mom" or the copy from "dad." Thus, with three chromosomes, there are 2 × 2 × 2 = 8 possible gametes. B. 1/64. The mother and father together can produce 8 × 8 = 64 different genetic combinations.

19-23 You have received exactly half of your genetic material from your mother, who received exactly half of her genetic material from her mother (your grandmother). A. Explain why it is unlikely that you share exactly one-quarter of your genetic material with your grandmother, and instead it is more accurate to say that in general people receive an average of one-quarter of their genetic endowment from each grandparent. B. Consider a gene on Chromosome 3 that you received from your grandmother. Is it likely you received an entire Chromosome 3 from your grandmother? Why or why not? C. What portion of your genetic material do you share with your sibling? Your aunt? Your cousin?

19-23 A. It is unlikely that you share exactly one-quarter of your genetic material with your grandmother, but it is true that organisms receive an average of one-quarter of their genes from each grandparent. When cells in your mother's germ line were undergoing meiosis, the chromosomes that she received from your grandmother and your grandfather were shuffled by recombination and then randomly assorted into the gametes. Each of these gametes probably received slightly less or slightly more than half of its genetic material from your grandmother. Thus, fusion of your mother's gamete with your father's created a zygote that shared approximately, but not exactly, one-quarter of its genes with your grandmother; this zygote divided repeatedly to form all the cells in your body. B. It is unlikely that you received the entire Chromosome 3 from your grandmother, because each chromosome undergoes at least one recombinational crossover with its homolog to ensure proper chromosome segregation in meiotic division I. C. You share an average of one-half of your genetic material with your sibling, one- quarter with your aunt, and one-eighth with your cousin. Because you and your sibling each get half of each parent's DNA, you have approximately half of your genetic material in common with your sibling. As your mother and her sister share approximately half of their genetic material, you and your aunt share 1/2 × 1/2 = 1/4. As your cousin has half of your aunt's genetic material, you share 1/2 × 1/4 = 1/8.

19-24 You examine a worm that has two genders: males that produce sperm and hermaphrodites that produce both sperm and eggs. The diploid adult has four homologous pairs of chromosomes that undergo very little recombination. Given a choice, the hermaphrodites prefer to mate with males, but just to annoy the worm, you pluck a hermaphrodite out of the wild and fertilize its eggs with its own sperm. Assuming that all the resulting offspring are viable, what fraction do you expect to be genetically identical to the parent worm? Assume that each chromosome in the original hermaphrodite is genetically distinct from its homolog. (a) all (b) none (c) 1/16 (d) 1/256

19-24 (c) 1/16 Because each chromosome is genetically distinct from its homolog, the parent is heterozygous for each chromosome and thus can produce 24 = 16 types of egg and 24 = 16 types of sperm. Any of the eggs produced will be able to give rise to an adult that is identical to the parent, but to do so it must be fertilized by the right type of sperm. For each type of egg, only one of the 16 possible sperm will produce a diploid that is identical to the parent. Therefore, one out of 16 of the offspring should be identical to the parent. In other words, a sexually reproducing organism with several heterozygous chromosomes has a relatively high probability of producing genetically distinct offspring even when the parent mates to itself.

Cytokinesis in animal cells ________________. (a) requires ATP. (b) leaves a small circular "scar" of actin filaments on the inner surface of the plasma membrane. (c) is often followed by phosphorylation of integrins in the plasma membrane. (d) is assisted by motor proteins that pull on microtubules attached to the cell cortex.

19-27 During recombination ________________________. (a) sister chromatids undergo crossing-over with each other. (b) chiasmata hold chromosomes together. (c) one crossover event occurs for each pair of human chromosomes. (d) the synaptonemal complex keeps the sister chromatids together until anaphase II.

19-27 Choice (b) is correct. Non-sister chromatids undergo crossing-over; because sister chromatids are identical, there would be no exchange of genetic material if sister chromatids underwent recombination [choice (a)]. The number of crossover events can vary for each meiosis; on average, two to three crossover events occur between each pair of human chromosomes [choice (c)]. Although the sister chromatids do not separate until anaphase II, their arms become unglued because the cohesins holding them together are degraded during anaphase I. The synaptonemal complex is important for holding together and aligning the duplicated homologs and is not involved directly in sister-chromatid cohesion [choice (d)].

19-29 Meiosis includes a recombination checkpoint that is analogous to the checkpoints in cell-cycle progression. Double-strand breaks in the DNA initiate recombination in meiosis. The broken end of a DNA molecule finds the corresponding sequence on a homologous chromosome and exchanges a chromosomal segment with its homolog, thereby repairing the break. Ongoing recombination sends a negative regulatory signal that prevents cells from entering meiotic division I. A. Mutations in several genes inactivate the recombination checkpoint. What do you predict will happen if a cell proceeds through meiotic division I before completing recombination? B. What will happen if a cell fails to initiate recombination and proceeds through meiotic division I? Meiotic division II?

19-29 A. If a cell proceeds through meiotic division I when its chromosomes are broken and incompletely repaired, segregation will be disastrous. Some recombination intermediates will be pulled to opposite spindle poles, thus breaking the DNA. Other chromosome fragments lacking centromeres will not be attached to microtubules and thus will segregate randomly, causing some meiotic products to have too little DNA and others to have too much. B. In the absence of recombination, the homologs will not segregate from each other properly in meiotic division I but the sister chromatids will segregate normally in meiotic division II. In meiotic division I, the unrecombined homologous chromosomes will not be held together by chiasmata. Thus, the homologous chromosomes will line up independently on the metaphase plate and segregate randomly, causing chromosome nondisjunction. Some products will have both homologs of a given chromosome and others will have none. In meiotic division II, the events will proceed normally and sister chromatids will be properly segregated to opposite poles. Nonetheless, because the chromosome sets at the start of meiotic division II were distributed unevenly, the gametes produced after meiotic division II will be aneuploid (that is, they will have an incorrect number of chromosomes).

19-32 Which of the following would *not* lead to aneuploidy during meiosis? (a) sister chromatids segregating inappropriately (b) non-sister chromatids segregating inappropriately (c) a reciprocal rearrangement of parts between nonhomologous chromosomes (for example, the left arm of Chromosome 2 exchanging places with the right arm of Chromosome 3) (d) an extra set of chromosomes produced during S phase (for example, if paternal Chromosome 3 were replicated twice)

19-32 (c) Aneuploidy describes cells with an incorrect chromosome number. A reciprocal rearrangement of parts between nonhomologous chromosomes will not lead to aneuploidy—it will simply change the assortment of genes attached to each centromere, while leaving the total amount of DNA and the total number of chromosomes unchanged.

19-33 A single nondisjunction event during meiosis ___________________. (a) will block recombination. (b) will occur only during meiosis II. (c) cannot occur with sex chromosomes. (d) will involve the production of two normal gametes if it occurs during meiosis II.

19-33 (d) A single nondisjunction event will lead to the segregation of one homologous pair of chromosomes, resulting in two aneuploid gametes and two normal gametes.

19-34 When a reciprocal translocation occurs, part of one chromosome is exchanged with a part of another chromosome. For example, one half of Chromosome 3 may now be found fused to Chromosome 10, and part of Chromosome 10 is now found fused to Chromosome 3. In a balanced reciprocal translocation, an even exchange of material occurs such that no genetic information is extra or missing. Individuals can carry balanced reciprocal translocations and be quite healthy. Consider the case where a gamete containing a balanced reciprocal translocation of a single chromosome is used to fertilize a genetically normal egg. Explain why individuals carrying a single balanced reciprocal translocation might have problems with chromosome segregation during meiosis but not in mitosis.

19-34 During meiosis, homologous chromosomes pair to form bivalents. The chromosomes with the translocations will have difficulty pairing with the homologous chromosomes of normal structure during meiosis. However, during mitosis, there is no need for the homologous chromosomes to interact.

19-35 During fertilization in humans, _______________________. (a) a wave of Ca2+ ions is released in the fertilized egg's cytoplasm. (b) only one sperm binds to the unfertilized egg. (c) a sperm moves in a random fashion until it encounters an egg. (d) several sperm pronuclei compete in the cytoplasm to fuse with the egg nucleus.

19-35 Choice (a) is correct. Many sperm can bind to an egg [choice (b)]. Cells surrounding the egg release a chemoattractant signal, attracting the sperm to the correct place; sperm are moving toward the chemoattractant signal and not moving randomly [choice (c)]. Mechanisms exist to ensure that only one sperm fertilizes each egg, and thus only one sperm pronucleus will reach the cytoplasm of the egg [choice (d)].

19-36 Do you agree or disagree with the following statement? Explain your answer. If a diploid organism has 16 chromosomes (and thus 8 pairs of homologous chromosomes), that organism can produce only 28 genetically different gametes.

19-36 Disagree. There are two distinct mechanisms for genetic variation in gametes. One method, the reassortment of chromosomes during meiosis, would result in a diploid organism with 16 chromosomes producing 28 genetically different gametes. However, a much greater number of genetically different gametes can be produced as a result of the recombination between chromosomes that occurs during every meiosis.

19-37 Which of the following statements about Mendel's experiments is *false*? (a) The pea plants could undergo both cross-fertilization and self-fertilization. (b) The true-breeding strains were homozygous for the traits that Mendel examined. (c) The egg can carry either the allele from the maternal or the paternal chromosome. (d) All traits that Mendel studied were recessive.

19-37 (d) The traits that Mendel studied were inherited in a discrete fashion. For this to occur, for each pair of alleles, one allele is necessarily dominant and the other is recessive.

19-4 Somatic cells ___________________________. (a) are not necessary for sexual reproduction in all eukaryotic organisms. (b) are used to produce germ-line cells when organisms reach sexual maturity (c) leave no progeny. (d) do not contain sex chromosomes.

19-4 Choice (c) is correct. Somatic cells are used to form the rest of the animal's body, which is required to support sexual reproduction even if these cells are not used to generate the germ cells [choice (a)]. Germ-line cells are generally specified early in development, before organisms reach sexual maturity [choice (b)]. Somatic cells do contain sex chromosomes [choice (d)].

19-43 Which of the following reasons was essential for Mendel to disprove the theory of blended inheritance? (a) The traits that Mendel examined all involved genes that did not display linkage. (b) The traits that Mendel examined all involved the reproductive structures of the pea plant. (c) Mendel pioneered techniques permitting the fusion of male and female gametes from the same plant to produce a zygote. (d) The traits that Mendel examined involved an allele that was dominant and an allele that was recessive.

19-43 (d) To see the traits disappear in the F1 generation and reappear in the F2 generation, one of the alleles for each trait needed to be dominant while the other was recessive. Although choices (a) and (b) are true, they were not necessary for Mendel to disprove the theory of blended inheritance. Choice (c) is untrue; the plants that Mendel worked with had both male and female reproductive structures and could self-fertilize naturally.

19-44 Which of the following reasons was essential for Mendel's law of independent assortment? (a) All the traits that Mendel examined involved genes that did not display linkage. (b) Several of the phenotypes that Mendel examined involved color. (c) Mendel observed chromosomal segregation in pea-plant cells. (d) Mendel carried out his experiments on plants and not on fungi.

19-44 (a) To see the 9:3:3:1 segregation from a dihybrid cross, the two traits cannot be linked. Although choice (b) is true, it was not necessary for Mendel to determine the law of independent assortment. Mendel did not observe chromosomal segregation [choice (c)]. The law of independent assortment holds true in animal, fungal, and plant cells.

19-45 Is the following statement true or false? Explain. The phenotype of an organism reflects all of the alleles carried by that individual.

19-45 False. The phenotype, or the observable traits, of an organism often does not fully reflect its genotype, or the catalog of all alleles in the chromosomes. The reason is that some alleles are dominant (call these A) and other alleles are recessive (a). An individual who is heterozygous (Aa) for a dominant allele will have the same phenotype as one who is homozygous (AA).

19-50 Sickle-cell anemia is caused by a mutant allele of a hemoglobin gene. Individuals with two mutant alleles have sickle-cell anemia. Individuals homozygous and heterozygous for the mutant gene are more resistant to malaria than those with two wild-type alleles. Is this mutation dominant, recessive, or co-dominant?

19-50 The classification of all mutations depends on the phenotypic feature under consideration. With regard to the sickle-cell anemia phenotype, the mutant allele is recessive because a heterozygous individual has the same healthy phenotype as a homozygous wild-type individual. With regard to the malaria phenotype, the mutant allele is dominant because a heterozygous individual has the same phenotype as a homozygous mutant individual, namely resistance to malaria. With regard to the phenotype as a whole, the two alleles could be said to be co-dominant.

19-46 Gregor Mendel studied pea plants and developed some very important ideas about how genes are inherited. These studies used plant strains that were true breeding and always produced progeny that had the same __________________ as the parent. These strains were true breeding because they were __________________ for the gene important for a specific trait. In other words, for these true-breeding strains, both chromosomes in the diploid pea plant carried the same __________________ of the gene. Mendel started out examining the inheritance of a single trait at a time, and then moved on to examining two traits at once in a __________________ cross. His studies examining the inheritance of two traits in one cross allowed him to discover what is now known as Mendel's law of __________________ assortment. Geneticists can study the inheritance of specific traits in humans by analyzing a __________________, which shows the phenotypes of different family members over several generations for a particular trait. allele chromosome dependent dihybrid genotype heterozygous homozygous independent monohybrid pedigree phenotype segregation

19-48 Gregor Mendel studied pea plants and developed some very important ideas about how genes are inherited. These studies used plant strains that were true breeding and always produced progeny that had the same *phenotype* as the parent. These strains were true breeding because they were *homozygous* for the gene important for a specific trait. In other words, for these true-breeding strains, both chromosomes in the diploid pea plant carried the same *allele* of the gene. Mendel started out examining the inheritance of a single trait at a time, and then moved on to examining two traits at once in a *dihybrid* cross. His studies examining the inheritance of two traits in one cross allowed him to discover what is now known as Mendel's law of *independent* assortment. Geneticists can study the inheritance of specific traits in humans by analyzing a *pedigree*, which shows the phenotypes of different family members over several generations for a particular trait.

19-49 Cystic fibrosis results from mutations in a single gene that lies on Chromosome 7. Only homozygous mutant (ff) individuals are sick; homozygous wild-type (FF) and heterozygous (Ff) individuals are healthy. A healthy married couple has one child with cystic fibrosis and the wife is pregnant with a second child. A. What is the genotype of the mother? The father? B. What is the chance that the second child will have cystic fibrosis?

19-49 A. The genotypes of the mother and father are the same: Ff. The only way that a child can have the disease is if both parents are carriers of the mutant cystic fibrosis gene. B. The chance that the second child will have cystic fibrosis is one-quarter. The chance that the mother will transmit her mutant f allele to the offspring is one- half, multiplied by an equal chance that the father will transmit his mutant f allele to the offspring: 1/2 × 1/2 = 1/4. (Having one child with cystic fibrosis does not change the probability of having another child with the disease.)

19-5 Which of the following statements about the benefits of sexual reproduction is false? (a) Sexual reproduction permits enhanced survival because the gametes that carry alleles enhancing survival in harsh environments are used preferentially during fertilization. (b) Unicellular organisms that can undergo sexual reproduction have an increased ability to adapt to harsh environments. (c) Sexual reproduction reshuffles genes, which is thought to help species survive in novel or varying environments. (d) Sexual reproduction can speed the elimination of deleterious alleles.

19-5 (a) Alleles enhancing survival in harsh environments will not be selected for until the organism encounters the harsh environment. - *FALSE*

DNA polymerase catalyzes the joining of a nucleotide to a growing DNA strand. What prevents this enzyme from catalyzing the reverse reaction? (a) hydrolysis of pyrophosphate (PPi) to inorganic phosphate (Pi) + Pi (b) release of PPi from the nucleotide (c) hybridization of the new strand to the template (d) loss of ATP as an energy source

19-51 You are given two true-breeding strains of hamster. One strain has white fur color and the other has a dark brown fur color. When you cross the white-fur strain to the dark-brown-fur strain, you obtain F1 progeny that have a light brown fur color. When you cross the F1 progeny with each other, 25% of the F2 generation have white fur, 25% have dark brown fur, and 50% have light brown fur. How many genes crucial for fur coloration differ between the two starting strains? Explain your answer.

19-51 One gene involved in determining fur color differs between these two strains. The white allele is not fully recessive to the dark brown allele. Therefore, any animal that is heterozygous (and has one white allele and one dark brown allele) will have a light brown fur color. Thus, the white allele and the dark brown allele are co-dominant. When two heterozygous animals are crossed together, 25% of the offspring will be homozygous for one allele, 25% will be homozygous for the other allele, and 50% will be heterozygous, exactly what is observed in the cross you performed.

19-52 Gene A is located near gene B on Chromosome 13 in humans. A mutation in the germ line of an individual with the haplotype AB generates gametes with the genotype Ab. Many descendants of this founder individual carry the b mutation, which predisposes carriers to high blood pressure. Initially, all descendants who inherit the b mutation also inherit the neighboring A allele. Through the generations, fewer and fewer descendants with the b mutation carry the A allele, and instead they have the a allele. (Individuals with A and a are equally healthy and fit.) Explain how the b and A alleles are separated.

19-52 Eventually, the b mutation will be separated from the A allele by meiotic recombination. Meiotic recombination exchanges portions of homologous chromosomes, and thereby generates great diversity among the gametes of each individual. The locations of the one to five exchanges per chromosome during meiosis in humans are more or less random. Thus, each passing generation increases the cumulative likelihood of a recombinational crossover between any two neighboring genes (A and b). Such a recombinational crossover in an individual heterozygous for both genes (Ab and aB) will separate two alleles that were originally linked (yielding AB and ab).

19-56 Do you agree or disagree with the following statement? Explain your answer. A trait that is found at a low frequency in the population has to be a recessive trait.

19-56 Disagree. The frequency of a trait in a population has nothing to do with its dominance or recessiveness. To test dominance or recessiveness, the segregation of this trait must be observed. For example, the defective version of the gene involved in Huntington's disease occurs at a relatively low frequency in the population but behaves in a dominant fashion to cause disease.

19-58 Haplotype blocks can be seen in humans because _______. (a) disease genes are found in haplotype blocks. (b) modern humans descended from a relatively small population of about 10,000 individuals that existed about two thousand generations ago. (c) some of our human ancestors interbred with Neanderthals. (d) new mutations cannot be introduced into existing haplotype blocks.

19-58 (b) The relatively small population of human ancestors means that the chromosomes in modern-day humans are a shuffled set of a relatively small number of chromosome sets. Because this small population existed only about two thousand generations ago, there hasn't been enough time for recombination to scramble these haplotype blocks. Disease genes can certainly be found in haplotype blocks [choice (a)], although this is not why haplotype blocks exist. Although genome analysis does show that some ancestors of modern humans did interbreed with Neanderthals, this is not the main reason for the existence of haplotype blocks [choice (c)]. New mutations can be introduced into an existing haplotype block, so choice (d) is untrue.

19-6 To reproduce sexually, an organism must create haploid __________________ cells, or __________________, from diploid cells via a specialized cell division called __________________. During mating, the father's haploid cells, called __________________ in animals, fuse with the mother's haploid cells, called __________________. Cell fusion produces a diploid cell called a __________________, which undergoes many rounds of cell division to create the entire body of the new individual. The cells produced from the initial fusion event include __________________ cells that form most of the tissues of the body as well as the __________________-line cells that give rise to the next generation of progeny. allele bivalent eggs gametes germ pollen meiosis somatic mitosis sperm pedigree zygote

19-6 To reproduce sexually, an organism must create haploid *germ* cells, or *gametes*, from diploid cells via a specialized cell division called *meiosis*. During mating, the father's haploid cells, called *sperm* in animals, fuse with the mother's haploid cells, called *eggs*. Cell fusion produces a diploid cell called a *zygote*, which undergoes many rounds of cell division to create the entire body of the new individual. The cells produced from the initial fusion event include *somatic* cells that form most of the tissues of the body as well as the *germ*-line cells that give rise to the next generation of progeny.

19-60 The single-nucleotide polymorphisms found in the human population __________________. (a) are important for genetic mapping because they represent mutations in genes important for human disease. (b) are rarely found among blood relatives. (c) can be linked into haplotype blocks. (d) arose mainly during the past 10,000 years.

19-60 (c) Haplotype blocks are segments of chromosomes spanning a set of single-nucleotide polymorphisms that are linked and tend to be inherited as a unit.

19-61 Which of the following statements about genome-wide association studies (GWAS) is *false*? (a) GWAS use SNPs to compare populations of people with disease and people without disease to look for SNPs more likely to be present in those with disease. (b) GWAS can be used even if more than one gene can cause the disease of interest. (c) Sometimes GWAS will identify SNPs that are associated with a disease but these SNPs do not affect the gene product of the gene that causes the disease. (d) Studies using GWAS only examine SNPs that occur very rarely (<0.001%) in the population, as those SNPs are most likely to cause disease.

19-61 (d) GWAS are best at detecting SNPs that are common in the human population. But because they are so common, these variants are likely to alter disease susceptibility slightly, as otherwise they would have been strongly selected against in the population during evolution (and therefore rare). Significant differences in the inheritance of a very rare SNP will be difficult to determine in a GWAS unless the number of people used in the study is extremely large.

Figure Q15-31: Once this protein is fully translocated, where will region Y be? (a) in the cytoplasm (b) in the ER lumen (c) inserted into the ER membrane (d) degraded by signal peptidase

19-64 Any two human beings typically have an estimated 0.1% difference in their nucleotide sequences, which is equivalent to about 3 million nucleotide differences. These differences are the basis of the SNPs used to construct genetic linkage maps. Some of these SNPs actually lie in the region of the DNA that codes for the protein, yet they have no effect on the phenotype of individuals carrying the SNP on both homologous chromosomes. Explain how some SNPs can lie within the portion of the DNA that codes for the protein and yet have no discernible effect on the protein's activity.

19-64 Because of the redundancy of the genetic code, in which more than one codon can code for the same amino acid, some single nucleotide changes may not cause changes in the amino acid coded for by that codon. Furthermore, some amino acid substitutions are neutral (for example, the substitution of a small, uncharged amino acid for another amino acid with similar properties)—that is, they have no perceptible effect on the function of the protein.

19-65 You decide to carry out genetic association studies and identify a SNP variant that is found significantly more often in individuals who have schizophrenia than in those who are not affected. This SNP is found within an intron of the SZP gene. A. Can you deduce that an abnormality of the SZP gene is a cause of increased risk of schizophrenia? B. Can you say whether the SNP variant itself is a cause?

19-65 A. No, you cannot be sure of this. The SZP gene would be a prime suspect, but the abnormality causing the heightened risk of schizophrenia might well lie instead in some other nearby gene. B. No, you cannot say for certain. Most point mutations in introns have no functional effect, but some can be functionally important. For example, the intronic SNP might alter an enhancer element that is lying within the intron and is involved in the regulation of SZP transcription; or it might affect the splicing of the SZP gene transcripts.

19-7 During sexual reproduction, novel mixtures of alleles are generated. This is because ______. (a) in all diploid species, two alleles exist for every gene. (b) a diploid individual has two different alleles for every gene. (c) every gamete produced by a diploid individual has several different alleles of a single gene. (d) during meiosis, the segregation of homologs is random such that different gametes end up with different alleles of each gene.

19-7 Choice (d) is correct. Many alleles can exist for any gene [choice (a)], and a diploid individual can have either two different or two identical alleles of any given gene [choice (b)]. Every gamete only has a single allele of any gene [choice (c)].

19-8 Which of the following does *not* describe a situation of asexual reproduction? (a) A bacterium multiplying by simple cell division. (b) Using a part of a plant to create a new independent plant. (c) Using in vitro fertilization to combine a sperm and an egg to create an embryo. (d) The parthenogenetic development of eggs produced by some species of lizards.

19-8 (c) Asexual reproduction gives rise to offspring that are genetically identical to the parent. The in vitro fertilization process requires gametes (sperm and egg), which when combined, will produce an offspring that is genetically distinct from either parent.

Which of the following is responsible for the most cancer cases? A) Tobacco smoke B) Ultraviolet light C) Red meat consumption D) Polychlorinated biphenyls (PCBs)

A) tobacco smoke

19-9 Both budding yeast and the bacteria E. coli are unicellular life. Which of the following statements explains why budding yeast can undergo sexual reproduction while E. coli cannot. (a) Unlike E. coli, budding yeast can alternate between a diploid state and a haploid state. (b) Unlike E. coli, budding yeast cannot multiply by undergoing cell division. (c) Unlike E. coli, haploid budding yeast cells can undergo meiosis to produce the gametes necessary for sexual reproduction. (d) E. coli DNA is unable to undergo homologous recombination, making it incapable of producing gametes.

19-9 Choice (a) is correct. The budding yeast can also multiply by undergoing cell division [choice (b)], although the diploid state can either reproduce by cell division or undergo meiosis to produce haploid gametes that can either fuse with another haploid gamete to form a diploid cell, or can become a free-living haploid cell that multiplies by cell division. A budding yeast cell must be diploid to undergo meiosis; haploid cells cannot undergo meiosis [choice (c)]. E. coli can undergo homologous recombination and uses this process for DNA repair [choice (d)]. In fact, E. coli can shuffle their genomes through a process of conjugation, where DNA is transferred from one bacterium to another and may get incorporated in the E. coli genetic material by recombination. Although this conjugation process can lead to the transfer of genetic material, it is not typically considered sexual reproduction.

Given the generic signaling pathway in Figure Q16-9, write the number corresponding to the item on the line next to the descriptor below. _________ receptor protein _________ effector proteins _________ intracellular signaling proteins _________ ligand

2,4,3,1

How much nucleotide divergence is there on average between species M and N?

2.0%

A finished draft of the human genome was published in ___________.

2004

Rank the following cytoskeletal filaments from smallest to largest in diameter (1 = smallest in diameter, 4 = largest) ______ intermediate filaments ______ microtubules ______ actin filament ______ myofibril

3 4 2 1

Rank the following types of cell signaling from 1 to 4, with 1 representing the type of signaling in which the signal molecule travels the least distance and 4 the type of signaling in which the signal molecule travels the largest distance. ______ paracrine signaling ______ contact-dependent signaling ______ neuronal signaling ______ endocrine signaling

3,1,2,4

10-11 During gel electrophoresis, DNA fragments _______________________. (a) travel through a matrix containing a microscopic network of pores. (b) migrate toward a negatively charged electrode. (c) can be visualized without stains or labels. (d) are separated on the basis of their sequence.

10-20 Figure Q10-20 depicts a strategy by which a DNA fragment produced by cutting with the EcoRI restriction nuclease can be joined to a DNA fragment produced by cutting DNA with the HaeIII restriction nuclease. Note that cutting DNA with EcoRI produces a staggered end, whereas cutting DNA with HaeIII produces a blunt end. Why must polymerase be added in this reaction? (a) Polymerase will fill in the staggered end to create a blunt end. (b) Polymerase is needed to seal nicks in the DNA backbone. (c) Polymerase will add nucleotides to the end produced by the HaeIII restriction nuclease. (d) Without polymerase, there will not be enough energy for the reaction to proceed.

10-25 A plasmid ______________. (a) can confer antibiotic resistance to a bacterium. (b) is a single-stranded circular DNA molecule that can undergo horizontal transfer among bacteria. (c) is a tool designed in the lab and never found in naturally occurring bacteria. (d) always becomes part of the bacterial chromosome during transformation.

T/F: Transporters are similar to channels, except that they are larger, allowing folded proteins as well as smaller organic molecules to pass through them

False

10-30 You want to design a DNA probe used for hybridization to isolate a clone from a cDNA library. Which of the following statements about DNA probes is true? (a) The shorter the DNA probe used to probe the library, the greater the number of colonies to which the probe might hybridize. (b) A DNA probe that contains sequences that span two exons is better suited to the purpose than a DNA probe that only contains sequences from one exon. (c) A DNA probe that contains sequences immediately upstream of the DNA that codes for the first methionine in the open reading frame will usually not hybridize to clones in a cDNA library. (d) Hybridization of a DNA probe to the plasmid of interest will permit the detection of the clone of interest; labeling of the DNA probe is not necessary.

10-4 You have a circular plasmid that can be cut by the restriction nuclease HindIII, as diagrammed in Figure Q10-4. If you were to cut this circular piece of DNA with HindIII, which of the answers below best predicts what you would get? (a) one linear piece of DNA (b) two circular pieces of DNA (c) two semicircular pieces of DNA (d) two linear pieces of DNA

10-43 Which of the following limits the use of PCR to detect and isolate genes? (a) The sequence at the beginning and end of the DNA to be amplified must be known. (b) It also produces large numbers of copies of sequences beyond the 5′ or 3′ end of the desired sequence. (c) It cannot be used to amplify cDNAs or mRNAs. (d) It will amplify only sequences present in multiple copies in the DNA sample.

10-47 Why is an excess of normal deoxyribonucleoside triphosphate molecules (dNTPs) needed during dideoxy sequencing? (a) DNA polymerase uses the dNTPs to synthesize a DNA molecule complementary to the molecule being sequenced. (b) dNTPs are consumed as energy to fuel the sequencing reactions. (c) When dNTP levels are too low, there will be very few chain-termination events. (d) The dNTPs can hybridize to the fragment to be sequenced and serve as primers for DNA polymerase.

10-53 Which of the following techniques is not appropriate if you want to examine the transcriptome of a specific tissue? (a) in situ hybridization (b) production of a cDNA library (c) RNA-Seq (d) microarray analysis

5-16 The DNA from two different species can often be distinguished by a difference in the ______________________. (a) ratio of A + T to G + C (b) ratio of A + G to C + T (c) ratio of sugar to phosphate (d) presence of bases other than A, G, C, and T

5-2 Many of the breakthroughs in modern biology came after Watson and Crick published their model of DNA in 1953. However, chromosomes were identified earlier. In what decade did scientists first identify chromosomes? (a) 1880s (b) 1920s (c) 1940s (d) 1780s

5-44 The chromosomes we typically see in images are isolated from mitotic cells. These mitotic chromosomes are in the most highly condensed form. Interphase cells contain chromosomes that are less densely packed and __________________________. (a) occupy discrete territories in the nucleus (b) share the same nuclear territory as their homolog (c) are restricted to the nucleolus (d) are completely tangled with other chromosomes

5-46 Specific regions of eukaryotic chromosomes contain sequence elements that are absolutely required for the proper transmission of genetic information from a mother cell to each daughter cell. Which of the following is not known to be one of these required elements in eukaryotes? (a) terminators of replication (b) origins of replication (c) telomeres (d) centromeres

5-47 Mitotic chromosomes are _____ times more compact than a DNA molecule in its extended form. (a) 10,000 (b) 100,000 (c) 1000 (d) 100

5-50 The classic "beads-on-a-string" structure is the most decondensed chromatin structure possible and is produced experimentally. Which chromatin components are not retained when this structure is generated? (a) linker histones (b) linker DNA (c) nucleosome core particles (d) core histones

5-62 Methylation and acetylation are common changes made to histone H3, and the specific combination of these changes is sometimes referred to as the "histone code." Which of the following patterns will probably lead to gene silencing? (a) lysine 9 methylation (b) lysine 4 methylation and lysine 9 acetylation (c) lysine 14 acetylation (d) lysine 9 acetylation and lysine 14 acetylation

5-64 Which of the following best describes the mechanism by which chromatin-remodeling complexes "loosen" the DNA wrapped around the core histones? (a) They use energy derived from ATP hydrolysis to change the relative position of the DNA and the core histone octamer (b) They chemically modify the DNA, changing the affinity between the histone octamer and the DNA (c) They remove histone H1 from the linker DNA adjacent to the core histone octamer (d) They chemically modify core histones to alter the affinity between the histone octamer and the DNA

5-8 Several experiments were required to demonstrate how traits are inherited. Which scientist or team of scientists first demonstrated that cells contain some component that can be transferred to a new population of cells and permanently cause changes in the new cells? (a) Griffith (b) Watson and Crick (c) Avery, MacLeod, and McCarty (d) Hershey and Chase

A friend declares that chromosomes are held at the metaphase plate by microtubules that push on each chromosome from opposite sides. Which of the following observations does not support your belief that the microtubules are pulling on the chromosomes? (a) the jiggling movement of chromosomes at the metaphase plate (b) the way in which chromosomes behave when the attachment between sister chromatids is severed (c) the way in which chromosomes behave when the attachment to one kinetochore is severed (d) the shape of chromosomes as they move toward the spindle poles at anaphase

A large protein that passes through the nuclear pore must have an appropriate _________. (a) sorting sequence, which typically contains the positively charged amino acids lysine and arginine. (b) sorting sequence, which typically contains the hydrophobic amino acids leucine and isoleucine. (c) sequence to interact with the nuclear fibrils. (d) Ran-interacting protein domain.

Cells in the G0 state ________________. (a) do not divide. (b) cannot re-enter the cell cycle. (c) have entered this arrest state from either G1 or G2. (d) have duplicated their DNA.

T/F: Ubiquinone can transfer only one electron in each cycle

False

Nonhomologous end joining can result in all but which of the following? (a) the recovery of lost nucleotides on a damaged DNA strand (b) the interruption of gene expression (c) loss of nucleotides at the site of repair (d) translocations of DNA fragments to an entirely different chromosome

Programmed cell death occurs ________________. (a) by means of an intracellular suicide program. (b) rarely and selectively only during animal development. (c) only in unhealthy or abnormal cells. (d) only during embryonic development.

Proteins that are fully translated in the cytosol and lack a sorting signal will end up in ____. (a) the cytosol. (b) the mitochondria. (c) the interior of the nucleus. (d) the nuclear membrane.

Sometimes, chemical damage to DNA can occur just before DNA replication begins, not giving the repair system enough time to correct the error before the DNA is duplicated. This gives rise to mutation. If the cytosine in the sequence TCAT is deaminated and not repaired, which of the following is the point mutation you would observe after this segment has undergone two rounds of DNA replication? (a) TTAT (b) TUAT (c) TGAT (d) TAAT

The repair of mismatched base pairs or damaged nucleotides in a DNA strand requires a multistep process. Which choice below describes the known sequence of events in this process? (a) DNA damage is recognized, the newly synthesized strand is identified by an existing nick in the backbone, a segment of the new strand is removed by repair proteins, the gap is filled by DNA polymerase, and the strand is sealed by DNA ligase. (b) DNA repair polymerase simultaneously removes bases ahead of it and polymerizes the correct sequence behind it as it moves along the template. DNA ligase seals the nicks in the repaired strand. (c) DNA damage is recognized, the newly synthesized strand is identified by an existing nick in the backbone, a segment of the new strand is removed by an exonuclease, and the gap is repaired by DNA ligase. (d) A nick in the DNA is recognized, DNA repair proteins switch out the wrong base and insert the correct base, and DNA ligase seals the nick.

What is the role of the nuclear localization sequence in a nuclear protein? (a) It is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore. (b) It is a hydrophobic sequence that enables the protein to enter the nuclear membranes. (c) It aids in protein unfolding so that the protein can thread through nuclear pores. (d) It prevents the protein from diffusing out of the nucleus through nuclear pores.

What part of the DNA replication process would be most directly affected if a strain of bacteria lacking helicase were used to make the cell extracts? (a) initiation of DNA synthesis (b) Okazaki fragment synthesis (c) leading-strand elongation (d) lagging-strand completion

What part of the DNA replication process would be most directly affected if a strain of bacteria lacking primase were used to make the cell extracts? (a) initiation of DNA synthesis (b) Okazaki fragment synthesis (c) leading-strand elongation (d) lagging-strand completion

Which of the following does not occur during M phase in animal cells? (a) growth of the cell (b) condensation of chromosomes (c) breakdown of nuclear envelope (d) attachment of chromosomes to microtubules

Which of the following precede the re-formation of the nuclear envelope during M phase in animal cells? (a) assembly of the contractile ring (b) decondensation of chromosomes (c) reassembly of the nuclear lamina (d) transcription of nuclear genes

Which of the following statements about kinetochores is true? (a) Kinetochores assemble onto chromosomes during late prophase. (b) Kinetochores contain DNA-binding proteins that recognize sequences at the telomere of the chromosome. (c) Kinetochore proteins bind to the tubulin molecules at the minus end of microtubules. (d) Kinetochores assemble on chromosomes that lack centromeres.

Which of the following statements about membrane-enclosed organelles is true? (a) In a typical cell, the area of the endoplasmic reticulum membrane far exceeds the area of plasma membrane. (b) The nucleus is the only organelle that is surrounded by a double membrane. (c) Other than the nucleus, most organelles are small and thus, in a typical cell, only about 10% of a cell's volume is occupied by membrane-enclosed organelles; the other 90% of the cell volume is the cytosol. (d) The nucleus is the only organelle that contains DNA.

Which of the following statements about peroxisomes is false? (a) Most peroxisomal proteins are synthesized in the ER. (b) Peroxisomes synthesize phospholipids for the myelin sheath. (c) Peroxisomes produce hydrogen peroxide. (d) Vesicles that bud from the ER can mature into peroxisomes.

Which of the following statements about phagocytic cells in animals is false? (a) Phagocytic cells are important in the gut to take up large particles of food. (b) Phagocytic cells scavenge dead and damaged cells and cell debris. (c) Phagocytic cells can engulf invading microorganisms and deliver them to their lysosomes for destruction. (d) Phagocytic cells extend pseudopods that surround the material to be ingested.

Which of the following statements about secretion is true? (a) The membrane of a secretory vesicle will fuse with the plasma membrane when it discharges its contents to the cell's exterior. (b) Vesicles for regulated exocytosis will not bud off the trans Golgi network until the appropriate signal has been received by the cell. (c) The signal sequences of proteins destined for constitutive exocytosis ensure their packaging into the correct vesicles. (d) Proteins destined for constitutive exocytosis aggregate as a result of the acidic pH of the trans Golgi network.

Which of the following statements about the cell cycle is false? (a) Once a cell decides to enter the cell cycle, the time from start to finish is the same in all eukaryotic cells. (b) An unfavorable environment can cause cells to arrest in G1. (c) A cell has more DNA during G2 than it did in G1. (d) The cleavage divisions that occur in an early embryo have short G1 and G2 phases.

Which of the following statements about vesicle budding from the Golgi is false? (a) Clathrin molecules are important for binding to and selecting cargoes for transport. (b) Adaptins interact with clathrin. (c) Once vesicle budding occurs, clathrin molecules are released from the vesicle. (d) Clathrin molecules act at the cytosolic surface of the Golgi membrane.

T/F: Ubiquinone is associated with the inner mitochondrial membrane as a protein-bound electron carrier molecule.

False

A pregnant mouse is exposed to high levels of a chemical. Many of the mice in her litter are deformed, but when they are interbred with each other, all their offspring are normal. Which two of the following statements could explain these results? (a) In the deformed mice, somatic cells but not germ cells were mutated. (b) The original mouse's germ cells were mutated. (c) In the deformed mice, germ cells but not somatic cells were mutated. (d) The toxic chemical affects development but is not mutagenic.

A and D

A calmodulin-regulated kinase (CaM-kinase) is involved in spatial learning and memory. This kinase is able to phosphorylate itself such that its kinase activity is now independent of the intracellular concentration of Ca2+. Thus the kinase stays active after Ca2+ levels have dropped. Mice completely lacking this CaM-kinase have severe spatial learning defects but are otherwise normal. A. Each of the following mutations also leads to similar learning defects. For each case explain why. (1) a mutation that prevents the kinase from binding ATP (2) a mutation that deletes the calmodulin-binding part of the kinase (3) a mutation that destroys the site of autophosphorylation B. What would be the effect on the activity of CaM-kinase if there were a mutation that reduced its interaction with the protein phosphatase responsible for inactivating the kinase?

A) 1. Protein kinases have a binding site for ATP, which is the source of the phosphate used for phosphoylating their target proteins. If the kinase cannot bind ATP, it will be inactive. 2. Because binding to calmodulin in the presence of Ca2+ activates CaM-kinases, deletion of the calmodulin binding portion would inactivate the kinase 3. A mutation that destroys the site of autophosphorylation will also impair the normal function of the kinase, because the kinase will become inactive as soon as Ca2+ levels decrease. B) The kinase would stay active for longer after a transient increase in intracellular Ca2+ concentration.

Which of the following genetic changes cannot convert a proto-oncogene into an oncogene? A) A mutation that introduces a stop codon immediately after the codon for the initiator methionine. B) A mutation within the coding sequence that makes the protein hyperactive. C) An amplification of the number of copies of the proto-oncogene, causing overproduction of the normal protein. D) A mutation in the promoter of the proto-oncogene, causing the normal protein to be transcribed and translated at an abnormally high level.

A) A mutation that introduces a stop codon immediately after the codon for the initiator methionine

Which of the following cell types, under appropriate conditions, can be kept proliferating indefinitely in culture and yet retain unrestricted developmental potential? A) Embryonic stem cells B) Somatic cells C) Proliferating precursor cells D) Germ cells

A) Embryonic stem cells

Which of the following statements about integrins is false? A) Integrins use adaptor proteins to interact with the microtubule cytoskeleton. B) Integrins can switch to an activated state by binding to an extracellular matrix molecule. C) Integrins can switch to an activated state by binding to an intracellular protein. D) An activated integrin molecule takes on an extended conformation.

A) Integrins use adaptor proteins to interact with the microtubule cytoskeleton

For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; each word or phrase should be used only once. Cells signal to one another in various ways. Some use extracellular signal molecules that are dissolved gases, such as _______A___________, which can diffuse easily into cells. Others use cytokines, which bind to cytokine receptors. Cytokine receptors have no intrinsic enzyme activity but are associated with cytoplasmic tyrosine kinases called _________B_________s, which become activated on the binding of cytokine to its receptor and go on to phosphorylate and activate cytoplasmic transcriptional regulators called _______C___________s. Some intracellular signaling pathways involve chains of protein kinases that phosphorylate each other, as seen in the ______D____________ signaling module. Lipids can also relay signals in the cell, as we observe when phospholipase C cleaves the sugar-phosphate head off a lipid molecule to generate the two small messenger molecules ______E____________ (which remains embedded in the plasma membrane) and ______F____________ (which diffuses into the cytosol). cyclic GMP MAP kinase STAT diacylglycerol NO TGF-β IP3 Ras JAK SMAD

A) NO B) JAK C) STAT D) MAP kinase E) diacylglycerol F) IP3

In somatic cells, if a base is mismatched in one new daughter strand during DNA replication, and is not repaired, what fraction of the DNA duplexes will have a permanent change in the DNA sequence after the second round of DNA replication? (a) 1/2 (b) 1/4 (c) 1/8 (d) 1/16

Two protein kinases, PK1 and PK2, work sequentially in an intracellular signaling pathway. You create cells that contain inactivating mutations in the genes that encode either PK1 or PK2 and find that these cells no longer respond to a particular extracellular signal. You also create cells containing a version of PK1 that is permanently active and find that the cells behave as though they are receiving the signal even when the signal is not present. When you introduce the permanently active version of PK1 into cells that have an inactivating mutation in PK2, you find that these cells also behave as though they are receiving the signal even when no signal is present. A. From these results, does PK1 activate PK2 or does PK2 activate PK1? Explain your answer. B. You now create a permanently active version of PK2 and find that cells containing this version behave as though they are receiving the signal even when the signal is not present. What do you predict will happen if you introduce the permanently active version of PK2 into cells that have an inactivating mutation in PK1?

A) Normally PK2 activates PK1. If PK1 is permanently activated, a response is seen independently of whether or not PK2 is present. B) You would predict that no response to the signal would be observed. PK2 usually needs to activate PK1 for the cells to respond to the signal. When PK2 is permanently activated in the absence of PK1, PK1 is not there to relay the signal.

A plant cell elongates in which direction? A) Perpendicular to the orientation of the cellulose microfibrils B) Parallel to the orientation of the cellulose microfibrils

A) Perpendicular to the orientation of the cellulose microfibrils

Which of the following is the plant equivalent of a gap junction? A) Plasmodesmata B) Adherens junctions C) Tight junctions D) Desmosomes

A) Plasmodesmata

Which of the following statements about plant cell walls is true? A) The microtubule cytoskeleton directs the orientation in which cellulose is deposited in the cell wall. B) The molecular components of the cell wall are the same in all plant tissues. C) Because plant cell walls are rigid, they are not deposited until the cell has stopped growing. D) The cellulose found in cell walls is produced as a precursor molecule in the cell and delivered to the extracellular space by exocytosis.

A) The microtubule cytoskeleton directs the orientation in which cellulose is deposited in the cell wall

Cancer is fundamentally which type of disease? A) A genetic disease B) A disease of obesity C) An environmental disease D) An infectious disease

A) a genetic disease

Indicate which of the three major classes of cytoskeletal elements each statement below refers to. A. monomer that binds ATP B. includes keratin and neurofilaments C. important for formation of the contractile ring during cytokinesis D. supports and strengthens the nuclear envelope E. their stability involves a GTP cap F. used in the eucaryotic flagellum G. a component of the mitotic spindle H. can be connected through desmosomes I. directly involved in muscle contraction J. abundant in filopodia

A) actin filaments B) intermediate filaments C) actin filaments D) intermediate filaments E) microtubules F) microtubules G) microtubules H) intermediate filaments I) actin filaments J) actin filaments

Identify the cytoskeletal structures depicted in the epithelial cells shown in Figure Q17-1.

A) actin filaments B) microtubules C) intermediate filaments

Which type of junction involves a connection to the actin cytoskeleton? A) adherens junctions B) desmosomes C) tight junctions D) gap junctions

A) adherens junctions

Induced pluripotent stem (iPS) cells ______________________. A) are created by the expression of a set of key genes in cells derived from adult tissues so that these cells can differentiate into a variety of cell types B) require a supply of donor egg cells, such as embryonic stem cells C) can differentiate into a greater variety of adult tissues than embryonic stem cells D) are created by nuclear transplantation

A) are created by the expression of a set of key genes in cells derived from adult tissues so that these cells can differentiate into a variety of cell types

Adherens junctions ______________________. A) can be used to bend epithelial sheets into tubes B) are most often found at the basal surface of cells C) are found only in adult tissues D) involve fibronectin and integrin interactions

A) can be used to bend epithelial sheets into tubes

Fibroblasts are found in which tissues? A) Connective B) Epithelial C) Neural D) Muscular

A) connective

Which of the following tissues is characterized by a plentiful extracellular matrix? A) Connective B) Epithelial C) Nervous D) Muscular

A) connective

Acetylcholine acts at a GPCR on heart muscle to make the heart beat more slowly. It does so by ultimately opening K+ channels in the plasma membrane (as diagrammed in Figure Q16-25), which decreases the cell's excitability by making it harder to depolarize the plasma membrane. Indicate whether each of the following conditions would increase or decrease the effect of acetylcholine. A. addition of a drug that stimulates the GTPase activity of the Gα subunit B. mutations in the K+ channel that keep it closed all the time C. modification of the Gα subunit by cholera toxin D. a mutation that decreases the affinity of the βγ complex of the G protein for the K+ channel E. a mutation in the acetylcholine receptor that prevents its localization on the cell surface F. adding acetylcholinesterase to the external environment of the cell

A) decrease B) decrease C) increase D) decrease E) decrease F) decrease

For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; each word or phrase should be used only once. Cells can signal to each other in various ways. A signal that must be relayed to the entire body is most efficiently sent by _________A_________ cells, which produce hormones that are carried throughout the body through the bloodstream. On the other hand, _______B___________ methods of cell signaling do not require the release of a secreted molecule and are used for very localized signaling events. During _____C_____________ signaling, the signal remains in the neighborhood of the secreting cell and thus acts as a local mediator on nearby cells. Finally, _______D___________ signaling converts electrical impulses into a chemical signal. Cells receive signals through a _________E_________, which can be an integral membrane protein or can reside inside the cell. amplification G-protein phosphorylation contact-dependent K+ channel receptor endocrine neuronal target epithelial paracrine

A) endocrine B) contact-dependent C) paracrine D) neuronal E) receptor

When adrenaline binds to adrenergic receptors on the surface of a muscle cell, it activates a G protein, initiating an intracellular signaling pathway in which the activated α subunit activates adenylyl cyclase, thereby increasing cAMP levels in the cell. The cAMP molecules then activate a cAMP-dependent kinase (PKA) that, in turn, activates enzymes that result in the breakdown of muscle glycogen, thus lowering glycogen levels. You obtain muscle cells that are defective in various components of the signaling pathway. Referring to Figure Q16-29, indicate how glycogen levels would be affected in the presence of adrenaline in the following cells. Would they be higher or lower than in normal cells treated with adrenaline? A. cells that lack adenylyl cyclase B. cells that lack the GPCR C. cells that lack cAMP phosphodiesterase D. cells that have an α subunit that cannot hydrolyze GTP but can interact properly with the β and γ subunits

A) higher B) higher C) lower D) lower

Receipt of extracellular signals can change cell behavior quickly (e.g., in seconds or less) or much more slowly (e.g., in hours). A. What kind of molecular changes could cause quick changes in cell behaviour? B. What kind of molecular changes could cause slow changes in cell behaviour? C. Explain why the response you named in A results in a quick change, whereas the response you named in B results in a slow change.

A) ion channels opening, phosphorylation B) changes in gene expression C) changes in gene expression take longer because they must undergo transcription and translation

Indicate by writing "yes" or "no" whether amplification of a signal could occur at the particular steps described below. Explain your answers. A. An extracellular signaling molecule binds and activates a GPCR. B. The activated GPCRs cause Gα to separate from Gβ and Gγ. C. Adenylyl cyclase produces cyclic AMP. D. cAMP activates protein kinase A. E. Protein kinase A phosphorylates target proteins.

A) no B) yes C) yes D) no E) yes

Plasmodesmata ______________________. A) permit small molecules to pass from one cell to another B) are found only in animal cells C) are closed by the neurotransmitter dopamine D) provide tensile strength

A) permit small molecules to pass from one cell to another

Cells export collagen to the extracellular matrix as: A) procollagen (a single-stranded collagen polypeptide chain with additional peptides at each end). B) a single-stranded collagen polypeptide chain. C) a triple-stranded collagen molecule. D) collagen fibrils (made up of collagen molecules). E) collagen fibers (made up of collagen fibrils)

A) procollagen (a single-stranded collagen polypeptide chain with additional peptides at each end)

For each of the following sentences, select the best word or phrase from the list below to fill in the blanks. Not all words or phrases will be used; each word or phrase should be used only once. An extracellular signal molecule can act to change a cell's behavior by acting through cell-surface ______A____________ that control intracellular signaling proteins. These intracellular signaling proteins ultimately change the activity of ________B__________ proteins that bring about cell responses. Intracellular signaling proteins can ________C__________ the signal received to evoke a strong response from just a few extracellular signal molecules. A cell that receives more than one extracellular signal at a time can ____D____ this information using intracellular signaling proteins. ______E___________ proteins can act as molecular switches, letting a cell know that a signal has been received. Enzymes that phosphorylate proteins, termed ___F________, can also serve as molecular switches; the actions of these enzymes are countered by the activity of ___G_______________. GMP-binding effector cleavage GTP-binding decrease decouple protein phosphatases esterases sterols neurotransmitter integrate convolute amplify AMP-binding protein kinases acetylase receptors autocrine

A) receptors B) effector C) amplify D) integrate E) GTP-binding F) protein kinases G) protein phosphatases

For each of the following sentences, select the best word or phrase from the list below to fill in the blanks. Not all words or phrases will be used; each word or phrase should be used only once. G-protein-coupled receptors (GPCRs) all have a similar structure with ______A____________ transmembrane domains. When a GPCR binds an extracellular signal, an intracellular G protein, composed of _________B_________ subunits, becomes activated. ________C__________ of the G-protein subunits are tethered to the plasma membrane by short lipid tails. When unstimulated, the α subunit is bound to ______D____________, which is exchanged for _______E___________ on stimulation. The intrinsic ________F__________ activity of the α subunit is important for inactivating the G protein. _______G___________ inhibits this activity of the α subunit, thereby keeping the subunit in an active state. phosphodiesterase five ATP GTP adenylyl cyclase GTPase seven cholera toxin Ca2+ four AMP twelve GDP cAMP diacylglycerol three ATPase two

A) seven B) three C) two D) GDP E) GTP F) GTPase G) cholera

You are interested in cell size regulation and discover that signaling through an enzyme-coupled receptor is important for the growth (enlargement) of mouse liver cells. Activation of the receptor activates adenylyl cyclase, which ultimately leads to the activation of PKA, which then phosphorylates a transcription factor called TFS on threonine 42. This phosphorylation is necessary for the binding of TFS to its specific sites on DNA, where it then activates the transcription of Sze2, a gene that encodes a protein important for liver cell growth. You find that liver cells lacking the receptor are 15% smaller than normal cells, whereas cells that express a constitutively activated version of PKA are 15% larger than normal liver cells. Given these results, predict whether you would expect the cell's size to be bigger or smaller than normal cells if cells were treated in the following fashion. A. You change threonine 42 on TFS to an alanine residue. B. You create a version of the receptor that is constitutively active. C. You add a drug that inhibits adenylyl cyclase. D. You add a drug that increases the activity of cyclic AMP phosphodiesterase. E. You mutate the cAMP-binding sites in the regulatory subunits of PKA, so that the complex binds cAMP more tightly.

A) smaller B) larger C) smaller D) smaller E) larger

The rod photoreceptors in the eye are extremely sensitive to light. The cells sense light through a signal transduction cascade involving light activation of a GPCR that activates a G protein that activates cyclic GMP phosphodiesterase. How would you expect the addition of the following drugs to affect the light-sensing ability of the rod cells? Explain your answers. A. a drug that inhibits cyclic GMP phosphodiesterase B. a drug that is a nonhydrolyzable analog of GTP

A) this drug would lead to the photoreceptor always signaling that it has not absorbed a photon B) this would lead the the photoreceptor always signaling it has absorbed a photon

For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; each word or phrase should be used only once. Ca2+ can trigger biological effects in cells because an unstimulated cell has an extremely _______A___________ concentration of free Ca2+ in the cytosol, compared with its concentration in the ______B____________ space and in the ______C____________, creating a steep electrochemical gradient. When Ca2+ enters the cytosol, it interacts with Ca2+-responsive proteins such as ______D____________, which also binds diacylglycerol, and ________E__________, which activates CaM-kinases. average extracellular nuclear phosopholipase C protein kinase C low peroxisome high Ca2+ adenylyl cyclase protein kinase A intracellular endoplasmic reticulum calmodulin colorful

A)A) low B) extracellular C) endoplasmic reticulum D) protein kinase C E) calmodulin

You are interested in studying kinesin movements. You therefore prepare silica beads and coat them with kinesin molecules so that each bead, on average, has only one kinesin molecule attached to it. You add these kinesin-coated beads to a preparation of microtubules you have polymerized. Using video microscopy, you watch the kinesin move down the microtubules. A. Kinesin-GFP has been measured to move along microtubules at a rate of 0.3 μm/sec, and single-molecule studies have revealed that kinesin moves along microtubules progressively, with each step being 8 nm. How many steps can the kinesin molecule take in 4 seconds, assuming that the kinesin stays attached to the microtubule for the entire 4 seconds? B. Because each kinesin molecule is thought to take approximately 100 steps before falling off the microtubule, will you see your silica beads detach from the microtubule during your 4 seconds of observation? C. What would you predict would happen to the kinesin-coated silica beads if you were to add AMP-PNP (a nonhydrolyzable ATP)

A. 150 steps (3 micrometers-300nm x 4 seconds = 1200nm/ 8 nm per step 150 steps) B. Yes, you should see silica beads detach some time during the 4 seconds of observation, because each kinesin will take more than 100 steps in that 4 sec time frame. C. if you were to add AMP-PNP you would no longer see silica beads moving down the microtubule. One molecule of ATP is hydrolyzed per sestep that kinesin takes; without ATP hydrolysis translocation of the beads will be inhibited. However, you may still see the beads associated with the microtubules, because AMP-PNP does not inhibit the association of kinesin with the microtubule.

In the budding yeast, activation of the GTP-binding protein Cdc42 occurs on binding of an external signal (pheromone) to a G-protein-linked receptor. Activation of Cdc42 promotes actin polymerization. Predict would happen to actin polymerization, in comparison with pheromone-treated cells, in the following cases. A. You add pheromone to an inhibitor of G-protein-linked receptors. B.You add pheromone to a nonhydrolyzable analogue of GTP.

A. Actin would not polymerize, the pheromone would not bind to the G-protein linked receptor because of the inhibitor. B. Actin would polymerize

The graph in Figure Q17-22 shows the time course of the polymerization of pure tubulin in vitro. You can assume that the starting concentration of free tubulin is much higher than it is in cells. A.Explain the reason for the initial lag in the rate of microtubule formation. B.Why does the curve level out after point C?

A. Before they can polymerize to form microtubules, tubulin molecules have to form small aggregates that act as nucleation centers. This aggregation step is slow because the molecules have to come together in the right configuration. Therefore there is a lag phase before the microtubules start to be formed. B. After point C an equilibrium point has been reached where the rates of polymerization and depolymerization are exactly balanced.

Indicate whether the following statements are true or false. If a statement is false, explain why it is false. A. When DNA is being replicated inside a cell, local heating occurs, allowing the two strands to separate. B. DNA replication origins are typically rich in G-C base pairs. C. Meselson and Stahl ruled out the dispersive model for DNA replication. D. DNA replication is a bidirectional process that is initiated at multiple locations along chromosomes in eukaryotic cells.

A. False B. False C. True. D. True.

T/F: Voltage-gated K+ channels also open immediately in response to local depolarization, reducing the magnitude of the action potential.

False

Indicate whether the following statements are true or false. If a statement is false, explain why it is false. A. The repair polymerase is the enzyme that proofreads the newly synthesized strands to ensure the accuracy of DNA replication. B. There is a single enzyme that degrades the RNA primers and lays down the corresponding DNA sequence behind it. C. DNA ligase is required to seal the sugar-phosphate backbone between all the DNA fragments on the lagging strand. D. The repair polymerase does not require the aid of the sliding clamp, because it is only synthesizing DNA over very short stretches.

A. False. B. False. C. True. D. True.

Indicate whether the following statements are true or false. If a statement is false, explain why it is false. A. Homologous recombination cannot occur in prokaryotic cells, because they are haploid, and therefore have no extra copy of the chromosome to use as a template for repair. B. The first step in repair requires a nuclease to remove a stretch of base pairs from the 5′ end of each strand at the site of the break. C. The 3′ overhang "invades" the homologous DNA duplex, which can be used as a primer for the repair DNA polymerase. D. The DNA template used to repair the broken strand is the homologous chromosome inherited from the other parent.

A. False. B. True. C. True. D. False.

You are curious about the dynamic instability of microtubules and decide to join a lab that works on microtubule polymerization. The people in the lab help you grow some microtubules in culture using conditions that allow you to watch individual microtubules under a microscope. You can see the microtubules growing and shrinking, as you expect. The professor who runs the lab gets in a new piece of equipment, a very fine laser beam that can be used to sever microtubules. She is very excited and wants to sever growing microtubules at their middle, using the laser beam. A. Do you predict that the newly exposed microtubule plus ends will grow or shrink? Explain your answer. B. What do you expect would happen to the newly exposed plus ends if you were to grow the microtubules in the presence of an analog of GTP that cannot be hydrolyzed, and you then severed the microtubules in the middle with a laser beam?

A. The newly exposed microtubule plus ends will most likely shrink if you sever the microtubules in the middle. This is because a microtubule grow by adding GTP carrying subunits to the plus end. The GTP is hydrolyzed over time, leaving only a cap of GTO-carrying subunits at the + end, with the remainder of the tubulin protofilament containing GDP- carrying subunits. Therefore, if you sever a growing microtubule in its middle, you will most likely create a plus end that contains GDP-carrying subunits. The GDP- carrying subunits are less tightly bound than the GTP-carrying subunits and will peel away from each other, causing depolymerization of the microtubule and shrinkage. B. If you were to polymerize the microtubules in the presence of a nonhydrolyzable analog of GTP and you then severed the microtubules with a laser, the newly exposed plus end would contain a GTP cap and so would probably continue to grow.

Using genetic engineering techniques, you have created a set of proteins that contain two (and only two) conflicting signal sequences that specify different compartments. Predict which signal would win out for the following combinations. Explain your answers. A. Signals for import into the nucleus and import into the ER. B. Signals for export from the nucleus and import into the mitochondria. C. Signals for import into mitochondria and retention in the ER.

A. The protein would enter the ER. The signal for a protein to enter the ER is recognized as the protein is being synthesized and the protein will end up either in the ER or on the ER membrane. Cytosolic nuclear transport proteins recognize proteins destined for the nucleus once those proteins are fully synthesized and fully folded. B. The protein would enter the mitochondria. For a nuclear export signal to work, the protein would have to end up in the nucleus first and thus would need a nuclear import signal for the nuclear export signal to be used. C. The protein would enter the mitochondria. To be retained in the ER, the protein needs to enter the ER. Because there is no signal for ER import, the ER retention signal would not function.

Indicate whether the following statements are true or false. If a statement is false, explain why it is false. A. Ionizing radiation and oxidative damage can cause DNA double-strand breaks. B. After damaged DNA has been repaired, nicks in the phosphate backbone are maintained as a way to identify the strand that was repaired. C. Depurination of DNA is a rare event that is caused by ultraviolet irradiation. D. Nonhomologous end joining is a mechanism that ensures that DNA double-strand breaks are repaired with a high degree of fidelity to the original DNA sequence.

A. True B. False. C. False. D. False.

Indicate whether the following statements are true or false. If a statement is false, explain why it is false. A. Primase is needed to initiate DNA replication on both the leading strand and the lagging strand. B. The sliding clamp is loaded once on each DNA strand, where it remains associated until replication is complete. C. Telomerase is a DNA polymerase that carries its own RNA molecule to use as a primer at the end of the lagging strand. D. Primase requires a proofreading function that ensures there are no errors in the RNA primers used for DNA replication.

A. True. B. False. C. True. D. False.

In the cell, the concentration of actin monomer is higher than the concentration required for purified actin monomers to polymerize in vitro. Thymosin is a protein that can bind actin monomers. If you were to add a drug that inhibits the ability of thymosin to bind actin monomers, what effect would this have on actin polymerization? Explain your answer.

Addition of a drug that keeps thymosin from binding actin monomer will increase the rate of actin polymerization in the cell. The reason is that actin monomers do not spontaneously form filaments in the cell, despite their high concentrations, is that the monomers are normally bound by proteins (such as thymosin) and are thereby prevented from adding to the end of an actin filament.

Do you agree or disagree with the following statement? Explain your answer. Nucleotide hydrolysis has a similar role in actin polymerization and in tubulin polymerization.

Agree: ATP bound actin monomers are added onto actin filaments; GTP bound tubulins subunits are added to the growing end of a microtubule. Nucleotide hydrolysis occurs after the addition of the subunit onto the filament in both actin and microtubules. ATP hydrolysis in actin polymerization decreases binding strength of monomoers in actin filaments, GTP hydrolysis during tubulin polymerization redueces strength of binding between tubulin. Nucleotide hydrolysis decreases the strength of binding between subunits and enhances depolymerization in actin filaments and microtubules.

Alternative exons can arise through the duplication and divergence of existing exons. What type of mutation below would be least tolerated during the evolution of a new exon? (a) a nucleotide change of A to G (b) a deletion of three consecutive bases (c) mutation of the first nucleotide in the intron (d) a nucleotide change that alters a TT dinucleotide to AA

T/F: When subjected to anaerobic conditions, glycolysis in mammalian cells continues and causes a buildup of pyruvate in the cytosol.

False

True or False Nearly every instance of DNA duplication leads to a newly functional gene

False

10-17 Which of the following statements about gel-transfer hybridization (or Southern blotting) is false? (a) This technique involves the transfer of DNA molecules from gel onto nitrocellulose paper or nylon paper. (b) In this technique, single-stranded DNA is separated by electrophoresis. (c) A labeled DNA probe binds to the DNA by hybridization. (d) The DNA that is separated on a gel is not labeled.

10-19 Figure Q10-19 shows the cleavage sites of several restriction nucleases.You cut a vector using the PciI restriction nuclease. Which of the following restriction nucleases will generate a fragment that can be ligated into this cut vector with the addition of only ligase and ATP? (a) HindIII (b) NcoI (c) MmeI (d) NspV

10-2 Which of the following statements about restriction nucleases is false? (a) A reproducible set of DNA fragments will be produced every time a restriction nuclease digests a known piece of DNA. (b) Restriction nucleases recognize specific sequences on single-stranded DNA. (c) Some bacteria use restriction nucleases as protection from foreign DNA. (d) Some restriction nucleases cut in a staggered fashion, leaving short, single-stranded regions of DNA at the ends of the cut molecule.

10-26 Which of the following statements about DNA libraries is true? (a) Production of a DNA library involves the direct insertion of short DNA fragments into bacteria through transformation. (b) By placing the library DNA into bacteria, the bacteria can be used to amplify the desired DNA fragments from the DNA library. (c) Individual bacteria that have taken up most of the library DNA are selected for during the construction of a DNA library. (d) The library DNA within the bacteria will only be replicated when it hybridizes to a DNA probe.

10-39 Starting with one double-stranded DNA molecule, how many cycles of PCR would you have to perform to produce about 100 double-stranded copies (assuming 100% efficiency per cycle)? (a) 2 (b) 7 (c) 25 (d) 100

10-40 Which of the following statements about PCR is false? (a) PCR uses a DNA polymerase from a thermophilic bacterium. (b) PCR is particularly powerful because after each cycle of replication, there is a linear increase in the amount of DNA available. (c) For PCR, every round of replication is preceded by the denaturation of the double-stranded DNA molecules. (d) The PCR will generate a pool of double-stranded DNA molecules, most of which will have DNA from primers at the 5′ ends.

10-5 You have a piece of circular DNA that can be cut by the restriction nucleases XhoI and SmaI, as indicated in Figure Q10-5. If you were to cut this circular piece of DNA with both XhoI and SmaI, how many fragments of DNA would you end up with? (a) 1 (b) 2 (c) 3 (d) 4

10-58 Insulin is a small protein that regulates blood sugar level and is given to patients who suffer from diabetes. Many years ago, diabetics were given insulin that had been purified from pig pancreas. Once recombinant DNA techniques became available, the DNA encoding insulin could be placed into an expression vector and insulin could be produced in bacteria. Which of the following is NOT a reason why purifying insulin from bacteria is a better way to produce insulin for diabetics than using insulin purified from a pig pancreas. (a) Insulin can be easily produced in large quantities from cells carrying the cloned DNA sequence. (b) The creation of transgenic pigs that expressed insulin was very expensive compared to the cost of creating bacteria that expressed insulin. (c) Insulin made from a bacterial culture and then purified will be free of any possible contaminating viruses that pigs (and any other animals) harbor. Since pigs are more closely related to people than bacteria are, their viruses are more likely to be harmful to people than are viruses that might infect bacteria. (d) The pig protein has slight amino acid differences compared to the human protein, so human insulin produced by bacteria will work better in people.

10-64 Figure Q10-64A depicts the restriction map of one segment of the human genome for four restriction nucleases W, X, Y, and Z. Figure Q10-64B depicts the restriction maps of four individual BAC clones that contain segments of human DNA from the region depicted in Figure Q10-64A.From this information, how would you order these BAC clones, from left to right? (a) 1, 2, 3, 4 (b) 2, 1, 4, 3 (c) 3, 4, 2, 1 (d) 4, 1, 3, 2

10-9 You have a linear piece of DNA that can be cut by the restriction nucleases HindIII and EcoRI, as diagrammed in Figure Q10-9. If you were to cut this linear DNA with HindIII, what type of DNA fragments do you predict you will obtain? (a) three linear pieces of DNA (b) two linear pieces of DNA, only one of which can be cut by EcoRI (c) two linear pieces of DNA, both of which can be cut by EcoRI (d) two linear pieces of DNA, only one of which can be cut by HindIII

5-10 Fred Griffith studied two strains of Streptococcus pneumonia, one that causes a lethal infection when injected into mice, and a second that is harmless. He observed that pathogenic bacteria that have been killed by heating can no longer cause an infection. But when these heat-killed bacteria are mixed with live, harmless bacteria, this mixture is capable of infecting and killing a mouse. What did Griffith conclude from this experiment? (a) The infectious strain cannot killed by heating (b) The heat-killed pathogenic bacteria "transformed" the harmless strain into a lethal one (c) The harmless strain somehow revived the heat-killed pathogenic bacteria (d) The mice had lost their immunity to infection with S. pneumoniae

5-25 The manner in which a gene sequence is related to its respective protein sequence is referred to as the _________ code. (a) protein (b) genetic (c) translational (d) expression

5-26 The information stored in the DNA sequences is used directly as a template to make ___________. (a) lipids (b) RNA (c) polypeptides (d) carbohydrates

5-3 Mitotic chromosomes were first visualized with the use of very simple tools: a basic light microscope and some dyes. Which of the following characteristics of mitotic chromosomes reflects how they were named? (a) motion (b) color (c) shape (d) location

5-35 The human genome is a diploid genome. However, when germ-line cells produce gametes, these specialized cells are haploid. What is the total number of chromosomes found in each of the gametes (egg or sperm) in your body? (a) 22 (b) 23 (c) 44 (d) 46

5-45 Figure Q5-45 clearly depicts the nucleolus, a nuclear structure that looks like a large, dark region when stained. The other dark, speckled regions in this image are the locations of particularly compact chromosomal segments called ____________. (a) euchromatin (b) heterochromatin (c) nuclear pores (d) nucleosomes

5-48 Interphase chromosomes are about______ times less compact than mitotic chromosomes, but still are about______ times more compact than a DNA molecule in its extended form. a) 10, 1000 (b) 20, 500 (c) 5, 2000 (d) 50, 200

5-56 Stepwise condensation of linear DNA happens in five different packing processes. Which of the following four processes has a direct requirement for histone H1? (a) formation of "beads-on-a-string" (b) formation of the 30-nm fiber (c) looping of the 30-nm fiber (d) packing of loops to form interphase chromosomes

5-61 The N-terminal tail of histone H3 can be extensively modified, and depending on the number, location, and combination of these modifications, these changes may promote the formation of heterochromatin. What is the result of heterochromatin formation? (a) increase in gene expression (b) gene silencing (c) recruitment of remodeling complexes (d) displacement of histone H1

5-65 Which of the following is not a chemical modification commonly found on core histone N-terminal tails? (a) methylation (b) hydroxylation (c) phosphorylation (d) acetylation

5-67 Most eukaryotic cells only express 20-30% of the genes they possess. The formation of heterochromatin maintains the other genes in a transcriptionally silent (unexpressed) state. Which histone modification directs the formation of the most common type of heterochromatin? (a) H3 lysine 4 methylation (b) H3 lysine 9 methylation (c) H3 lysine 14 methylation (d) H3 lysine 27 methylation

A cell with nuclear lamins that cannot be phosphorylated in M phase will be unable to ________________. (a) reassemble its nuclear envelope at telophase. (b) disassemble its nuclear lamina at prometaphase. (c) begin to assemble a mitotic spindle. (d) condense its chromosomes at prophase.

An individual transport vesicle ________. (a) contains only one type of protein in its lumen. (b) will fuse with only one type of membrane. (c) is endocytic if it is traveling toward the plasma membrane. (d) is enclosed by a membrane with the same lipid and protein composition as the membrane of the donor organelle.

DNA polymerases are processive, which means that they remain tightly associated with the template strand while moving rapidly and adding nucleotides to the growing daughter strand. Which piece of the replication machinery accounts for this characteristic? (a) helicase (b) sliding clamp (c) single-strand binding protein (d) primase

Fatty acids can easily be used to generate energy for the cell. Which of the following fatty acids will yield more energy? (a) CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH=CH-COOH (b) CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-COOH (c) CH3-CH=CH-CH2-CH2-CH2-CH2-CH=CH-COOH (d) CH3-CH2-CH2-CH2-CH2-CH2-CH2-COOH

Given Figure Q15-34, which of the following statements must be true? (a) The N-terminus of this protein is cytoplasmic. (b) The C-terminus of this protein is cytoplasmic. (c) The mature version of this protein will span the membrane twice, with both the N- and C-terminus in the cytoplasm. (d) None of the above.

Homologous recombination is an important mechanism in which organisms use a "backup" copy of the DNA as a template to fix double-strand breaks without loss of genetic information. Which of the following is not necessary for homologous recombination to occur? (a) 3′ DNA strand overhangs (b) 5′ DNA strand overhangs (c) a long stretch of sequence similarity (d) nucleases

How many replication forks are formed when an origin of replication is opened? (a) 1 (b) 2 (c) 3 (d) 4

Initiator proteins bind to replication origins and disrupt hydrogen bonds between the two DNA strands being copied. Which of the factors below does not contribute to the relative ease of strand separation by initiator proteins? (a) replication origins are rich in A-T base pairs (b) the reaction can occur at room temperature (c) they only separate a few base pairs at a time (d) once opened, other proteins of the DNA replication machinery bind to the origin

Molecules to be packaged into vesicles for transport are selected by ________. (a) clathrin. (b) adaptins. (c) dynamin. (d) SNAREs.

Progression through the cell cycle requires a cyclin to bind to a Cdk because _________. (a) the cyclins are the molecules with the enzymatic activity in the complex. (b) the binding of a cyclin to Cdk is required for Cdk enzymatic activity. (c) cyclin binding inhibits Cdk activity until the appropriate time in the cell cycle. (d) without cyclin binding, a cell-cycle checkpoint will be activated.

Sickle-cell anemia is an example of an inherited disease. Individuals with this disorder have misshapen (sickle-shaped) red blood cells caused by a change in the sequence of the β-globin gene. What is the nature of the change? (a) chromosome loss (b) base-pair change (c) gene duplication (d) base-pair insertion

The DNA duplex consists of two long covalent polymers wrapped around each other many times over their entire length. The separation of the DNA strands for replication causes the strands to be "overwound" in front of the replication fork. How does the cell relieve the torsional stress created along the DNA duplex during replication? (a) Nothing needs to be done because the two strands will be separated after replication is complete. (b) Topoisomerases break the covalent bonds of the backbone allowing the local unwinding of DNA ahead of the replication fork. (c) Helicase unwinds the DNA and rewinds it after replication is complete. (d) DNA repair enzymes remove torsional stress as they replace incorrectly paired bases.

The classic experiments conducted by Meselson and Stahl demonstrated that DNA replication is accomplished by employing a ________________ mechanism. (a) continuous (b) semiconservative (c) dispersive (d) conservative

What part of the DNA replication process would be most directly affected if a strain of bacteria lacking single-strand binding protein were used to make the cell extracts? (a) initiation of DNA synthesis (b) Okazaki fragment synthesis (c) leading-strand elongation (d) lagging-strand completion

Which of the following events does not usually occur during interphase? (a) Cells grow in size. (b) The nuclear envelope breaks down. (c) DNA is replicated. (d) The centrosomes are duplicated.

Which of the following statements about sequence proofreading during DNA replication is false? (a) The exonuclease activity is in a different domain of the DNA polymerase. (b) The exonuclease activity cleaves DNA in the 5′-to-3′ direction. (c) The DNA proofreading activity occurs concomitantly with strand elongation. (d) If an incorrect base is added, it is "unpaired" before removal.

Which of the following statements about the endoplasmic reticulum (ER) is false? (a) The ER is the major site for new membrane synthesis in the cell. (b) Proteins to be delivered to the ER lumen are synthesized on smooth ER. (c) Steroid hormones are synthesized on the smooth ER. (d) The ER membrane is contiguous with the outer nuclear membrane.

Which of the following statements about the protein quality control system in the ER is false? (a) Chaperone proteins help misfolded proteins fold properly. (b) Proteins that are misfolded are degraded in the ER lumen. (c) Protein complexes are checked for proper assembly before they can exit the ER. (d) A chaperone protein will bind to a misfolded protein to retain it in the ER.

Which of the following statements about transport into mitochondria and chloroplasts is false? (a) The signal sequence on proteins destined for these organelles is recognized by a receptor protein in the outer membrane of these organelles. (b) After a protein moves through the protein translocator in the outer membrane of these organelles, the protein diffuses in the lumen until it encounters a protein translocator in the inner membrane. (c) Proteins that are transported into these organelles are unfolded as they are being transported. (d) Signal peptidase will remove the signal sequence once the protein has been imported into these organelles.

Which of the following statements is false? (a) DNA synthesis begins at origins of replication. (b) The loading of the origin recognition complexes (ORCs) is triggered by S-Cdk. (c) The phosphorylation and degradation of Cdc6 help to ensure that DNA is replicated only once in each cell cycle. (d) DNA synthesis can only begin after prereplicative complexes assemble on the ORCs.

Which of the following statements is not an accurate statement about thymine dimers? (a) Thymine dimers can cause the DNA replication machinery to stall. (b) Thymine dimers are covalent links between thymidines on opposite DNA strands. (c) Prolonged exposure to sunlight causes thymine dimers to form. (d) Repair proteins recognize thymine dimers as a distortion in the DNA backbone.

Which of the following statements is true? (a) Lysosomes are believed to have originated from the engulfment of bacteria specialized for digestion. (b) The nuclear membrane is thought to have arisen from the plasma membrane invaginating around the DNA. (c) Because bacteria do not have mitochondria, they cannot produce ATP in a membrane-dependent fashion. (d) Chloroplasts and mitochondria share their DNA.

Which organelle fragments during mitosis? (a) endoplasmic reticulum (b) Golgi apparatus (c) mitochondrion (d) chloroplast

You are working in a biotech company that has discovered a small-molecule drug called H5434. H5434 binds to LDL receptors when they are bound to cholesterol. H5434 binding does not alter the conformation of the LDL receptor's intracellular domain. Interestingly, in vitro experiments demonstrate that addition of H5434 increases the affinity of LDL for cholesterol and prevents cholesterol from dissociating from the LDL receptor even in acidic conditions. Which of the following is a reasonable prediction of what may happen when you add H5434 to cells? (a) Cytosolic cholesterol levels will remain unchanged relative to normal cells. (b) Cytosolic cholesterol levels will decrease relative to normal cells. (c) The LDL receptor will remain on the plasma membrane. (d) The uncoating of vesicles will not occur.

You create cells with a version of Cdc6 that cannot be phosphorylated and thus cannot be degraded. Which of the following statements describes the likely consequence of this change in Cdc6? (a) Cells will enter S phase prematurely. (b) Cells will be unable to complete DNA synthesis. (c) The origin recognition complex (ORC) will be unable to bind to DNA. (d) Cdc6 will be produced inappropriately during M phase.

You have isolated a strain of mutant yeast cells that divides normally at 30°C but cannot enter M phase at 37°C. You have isolated its mitotic cyclin and mitotic Cdk and find that both proteins are produced and can form a normal M-Cdk complex at both temperatures. Which of the following temperature-sensitive mutations could not be responsible for the behavior of this strain of yeast? (a) inactivation of a protein kinase that acts on the mitotic Cdk kinase (b) inactivation of an enzyme that ubiquitylates M cyclin (c) inactivation of a phosphatase that acts on the mitotic Cdk kinase (d) a decrease in the levels of a transcriptional regulator required for producing sufficient amounts of M cyclin

What is the difference between a malignant and benign tumor? A) A malignant tumor proliferates in defiance of normal constraints, while a benign tumor does not. B) A malignant tumor invades and colonizes other tissues, while a benign tumor does not. C) A benign tumor can be treated while a malignant tumor cannot be treated

B) A malignant tumor invades and colonizes other tissues, while a benign tumor does not

Which of the following statements about tumor suppressor genes is false? A) Gene amplification of a tumor suppressor gene is less dangerous than gene amplification of a proto-oncogene. B) Cells with one functional copy of a tumor suppressor gene will usually proliferate faster than normal cells. C) Inactivation of tumor suppressor genes leads to enhanced cell survival and proliferation. D) Individuals with only one functional copy of a tumor suppressor gene are more prone to cancer than individuals with two functional copies of a tumor suppressor gene.

B) Cells with one functional copy of a tumor suppressor gene will usually proliferate faster than normal cells

In desmosomes, cadherin molecules are anchored inside an epithelial cell to which type of cytoskeletal filament? A) Microtubules B) Intermediate filaments C) Actin filaments

B) Intermediate filaments

About 50% of all human cancers have mutations in the p53 gene. What is the normal function of the p53 protein? A) It shuts down metabolism when DNA is damaged. B) It directs cells to die or stop dividing when DNA is damaged. C) It promotes motility allowing cells to avoid carcinogens. It repairs damaged DNA.

B) It directs cells to die or stop dividing when DNA is damaged.

A single mutation can activate which class of cancer causing gene? A) DNA repair gene B) Oncogene C) Tumor suppressor gene

B) Oncogene

In a tissue, which of the following cell types divides to create a continuous supply of differentiated cells? A) Fibroblasts B) Stem cells C) Epithelial cells D) Glial cells

B) Stem cells

Which of the following is NOT true of the basal lamina? A) The basal lamina is a thin tough sheet of extracellular matrix. B) The basal lamina lines the inside of epithelia cells at the basal membrane surface. C) The basal lamina contains a specialized type of collagen (type IV collagen).

B) The basal lamina lines the inside of epithelia cells at the basal membrane surface.

Which feature of glycosaminoglycans allows the extracellular matrix in cartilage to resist compression? A) Glycosaminoglycans are typically attached to proteins, and together these molecules help fill the space of the extracellular matrix. B) The negative charges on glycosaminoglycans attract sodium ions, which in turn draw a large amount of water into the extracellular matrix. C) Glycosaminoglycans form stiff rods in the extracellular matrix.

B) The negative charges on glycosaminoglycans attract sodium ions, which in turn draw a large amount of water into the extracellular matrix

Which of the following is NOT true of gap junctions? A) They allow inorganic ions and small water-soluble molecules to move directly between cells. B) They allow ATP-driven pumps to move substances from one cell to another. C) They allow an electrical and a metabolic coupling between the cells. D) They may be opened or closed as needed

B) They allow ATP-driven pumps to move substances from one cell to another

Proteoglycans in the extracellular matrix of animal tissues ________________. A) chiefly provide tensile strength B) allow cartilage to resist compression C) are linked to microtubules through the plasma membrane D) are polysaccharides composed of glucose subunits

B) allow cartilage to resist compression

Cells that are terminally differentiated ______________________. A) will undergo apoptosis within a few days B) can no longer undergo cell division C) are unable to move D) no longer produce RNAs

B) can no longer undergo cell division

What gives the plant cell wall its tensile strength? A) Starch B) Cellulose C) Actin D) Myosin

B) cellulose

In connective tissues, the tensile strength of the tissue is chiefly provided by: A) proteoglycans. B) collagen. C) actin. D) cellulose.

B) collagen

Supportive tissues, such as bone or wood, derive their strength from: A) cells. B) extracellular matrix. C) cytoskeletal filaments.

B) extracellular matrix

5-59 Although the chromatin structure of interphase and mitotic chromosomes is very compact, DNA-binding proteins and protein complexes must be able to gain access to the DNA molecule. Chromatin-remodeling complexes provide this access by __________________. (a) recruiting other enzymes (b) modifying the N-terminal tails of core histones (c) using the energy of ATP hydrolysis to move nucleosomes (d) denaturing the DNA by interfering with hydrogen-bonding between base pairs

Intermediate filaments are made from elongated fibrous proteins that are assembled into a ropelike structure. Figure Q17-7 shows the structure of an intermediate filament subunit. You are interested in how intermediate filaments are formed, and you create an intermediate filament subunit whose α-helical region is twice as long as that of a normal intermediate filament by duplicating the normal α-helical region while keeping a globular head at the N-terminus and a globular tail at the C-terminus; you call this subunit IFαd. If you were to assemble intermediate filaments using IF2αd as the subunit, which of the following predictions below describes the most likely outcome? (a) Filaments assembled using IFαd will interact with different cytoskeletal components. (b) Filaments assembled using IFαd will form dimers that are twice as long as dimers assembled from normal intermediate filaments. (c) Sixteen tetramers assembled from IFαd will be needed for a ropelike structure to form. (d) Dimers of IFαd will form by interactions with the N-terminal globular head and the C-terminal globular tail.

B) filaments assembled using IFαd will form dimers that are twice as long as dimers assembled from normal intermediate filaments.

Epithelial cells are attached to the basal lamina by: A) desmosomes. B) hemidesmosomes. C) cadherins. D) tight junctions

B) hemidesmosomes

At desmosomes, cadherin molecules are connected to ________________. A) actin filaments B) intermediate filaments C) microtubules D) gap junctions

B) intermediate filaments

A basal lamina ______________________. A) is a thin layer of connective tissue cells and matrix underlying an epithelium B) is a thin layer of extracellular matrix underlying an epithelium C) is attached to the apical surface of an epithelium D) separates epithelial cells from each other

B) is a thin layer of extracellular matrix underlying an epithelium

Cadherin proteins: A) create an electrical and metabolic coupling between epithelial cells. B) link epithelial cells together by binding to similar cadherins in adjacent epithelial cells. C) allow ions and small molecules to pass from one plant cell to another. D) anchor epithelial cells to the basal lamina

B) link epithelial cells together by binding to similar cadherins in adjacent epithelial cells

Cadherins ______________________. A) are used to transfer proteins from one cell to another B) mediate cell-cell attachments through homophilic interactions C) are abundant in the plant cell wall D) bind to collagen fibrils

B) mediate cell-cell attachments through homophilic interactions

A major distinction between the connective tissues in an animal and other main tissue types such as epithelium, nervous tissue, or muscle is _______________. A) the ability of connective tissue cells such as fibroblasts to change shape B) the amount of extracellular matrix in connective tissues C) the ability of connective tissues to withstand mechanical stresses D) the numerous connections that connective tissue cells make with each other

B) the amount of extracellular matrix in connective tissues

Of the following mutations, which are likely to cause cell-cycle arrest? A. a mutation in a gene encoding a cell-surface mitogen receptor that makes the receptor active even in the absence of the mitogen B. a mutation that destroyed the kinase activity of S-Cdk C. a mutation that allowed G1-Cdk to be active independently of its phosphorylation status D. a mutation that removed the phosphorylation sites on the Rb protein E. a mutation that inhibited the activity of Rb

B, D

Irradiated mammalian cells usually stop dividing and arrest at a G1 checkpoint. Place the following events in the order in which they occur. A. production of p21 B. DNA damage C. inhibition of cyclin-Cdk complexes D. accumulation and activation of p53

B, D, A, C

8-8 Which of these method(s) of controlling eukaryotic gene expression is NOT employed in prokaryotic cells? A. controlling how often a gene is transcribed B. controlling how an RNA transcript is spliced C. controlling which mRNAs are exported from the nucleus to the cytosol D. controlling which mRNAs are translated into protein by the ribosomes E. controlling how rapidly proteins are destroyed once they are made

B. controlling how an RNA transcript is spliced C. controlling which mRNAs are exported from the nucleus to the cytosol

10-1 Recombinant DNA technologies involve techniques that permit the creation of custom-made DNA molecules that can be introduced back into living organisms. These technologies were first developed in the ______. (a) 1930s. (b) 1950s. (c) 1970s. (d) 1990s.

10-14 A double-stranded DNA molecule can be separated into single strands by heating it to 90°C because _______________________. (a) heat disrupts the hydrogen bonds holding the sugar-phosphate backbone together. (b) DNA is negatively charged. (c) heat disrupts hydrogen-bonding between complementary nucleotides. (d) DNA is positively charged.

10-16 During DNA renaturation, two DNA strands will ________. (a) break the covalent bonds that hold the nucleotides together while maintaining the hydrogen bonds that hold the two strands together. (b) break the hydrogen bonds that hold the two strands together with no effect on the covalent bonds that hold the nucleotides together. (c) re-form a double helix if the two strands have complementary sequences. (d) re-form a double helix if the two strands are identical in sequence.

The process of DNA replication requires that each of the parental DNA strands be used as a ___________________ to produce a duplicate of the opposing strand. (a) catalyst (b) competitor (c) template (d) copy

True or false - A tissue is made of a single type of cell bound together by extracellular matrix

False

10-27 Which of the following statements about genomic DNA libraries is false? (a) The larger the size of the fragments used to make the library, the fewer colonies you will have to examine to find a clone that hybridizes to your probe. (b) The larger the size of the fragments used to make the library, the more difficult it will be to find your gene of interest once you have identified a clone that hybridizes to your probe. (c) The larger the genome of the organism from which a library is derived, the larger the fragments inserted into the vector will tend to be. (d) The smaller the gene you are seeking, the more likely it is that the gene will be found on a single clone.

10-3 You have purified DNA from your recently deceased goldfish. Which of the following restriction nucleases would you use if you wanted to end up with DNA fragments with an average size of 70 kilobase pairs (kb) after complete digestion of the DNA? The recognition sequence for each enzyme is indicated in the right-hand column. (a) Sau3AI GATC (b) BamHI GGATCC (c) NotI GCGGCCGC (d) XzaI GAAGGATCCTTC

10-38 PCR was invented in _______. (a) the 1800s. (b) the 1950s. (c) the 1980s. (d) 2009.

10-45 Your friend works at the Centers for Disease Control and Prevention and has discovered a brand-new virus that has recently been introduced into the human population. She has just developed a new assay that allows her to detect the virus by using PCR products made from the blood of infected patients. The assay uses primers in the PCR assay that hybridize to sequences in the viral genome. Your friend is distraught because of the result she obtained (see Figure Q10-45) when she looked at PCR products made using the blood of three patients suffering from the viral disease, using her own blood, and using a leaf from her petunia plant. You advise your friend not to panic, as you believe she is missing an important control. Which one of the choices listed below is the best control for clarifying the results of her assay? Explain your answer. (a) a PCR assay using blood from a patient who is newly infected but does not yet show symptoms (b) a PCR assay using blood from a dog (c) a PCR assay using blood from an uninfected person (d) repeating the experiments she has already done with a new tube of polymerase

10-48 Why are dideoxyribonucleoside triphosphates used during DNA sequencing? (a) They cannot be incorporated into DNA by DNA polymerase. (b) They are incorporated into DNA particularly well by DNA polymerases from thermophilic bacteria. (c) Incorporation of a dideoxyribonucleoside triphosphate leads to the termination of replication for that strand. (d) Dideoxyribonucleoside triphosphates are more stable than deoxyribonucleoside triphosphates.

10-51 With fully automated Sanger sequencing, all four chain-terminating ddNTPs can be added into a single reaction. This is different from the traditional slab gel Sanger sequencing, where a different reaction had to be carried out for each ddNTP. The mixing of all four ddNTPs can be carried out because ______________. (a) the fully automated Sanger sequencing reactions are loaded onto a capillary gel. (b) the fully automated Sanger sequencing reactions utilize ddNTPs each labeled with a different fluorescent tag, which allows all four ddNTPs to be incorporated into a single molecule of DNA. (c) the fully automated Sanger sequencing reactions generate a set of products, each of which carries a single fluorescent tag whose color reveals the identity of the base that is at the end of the product. (d) the fully automated Sanger sequencing reactions do not require DNA polymerase because the bases are read as the DNA is pulled through a tiny pore at the end of the capillary gel.

10-55 You create a recombinant DNA molecule that fuses the coding sequence of green fluorescent protein to the regulatory DNA sequences that control the expression of your favorite genes. Which of the following pieces of information can you NOT gain by examining the expression of this reporter gene? (a) the tissue where the protein encoded by this gene is expressed (b) the cell in which the protein encoded by this gene is expressed (c) the specific location within the cell of the protein encoded by this gene (d) when, during an organism's development, this gene is expressed

10-56 Which of the following statements about RNA interference (or RNAi) is false? (a) RNAi is a natural mechanism used to regulate genes. (b) During the process of RNAi, hybridization of a small RNA molecule with the mRNA degrades the mRNA. (c) Because RNAi depends on the introduction of a double-stranded RNA into a cell or an organism, it is not a process that can cause heritable changes in gene expression. (d) In C. elegans, RNAi can be introduced into the animals by feeding them with bacteria that produce the inhibitory RNA molecules.

10-59 Which of the following describes a feature found in bacterial expression vectors but not in cloning vectors? (a) origin of replication (b) cleavage sites for restriction nucleases (c) promoter DNA sequences (d) a polyadenylation signal

5-14 Which of the following structural characteristics is not normally observed in a DNA duplex? (a) purine-pyrimidine pairs (b) external sugar-phosphate backbone (c) uniform left-handed twist (d) antiparallel strands

5-18 Which DNA base pair is represented in Figure Q5-18? (a) A-T (b) T-A (c) G-C (d) C-G

5-36 What type of macromolecule helps package DNA in eukaryotic chromosomes? (a) lipids (b) carbohydrates (c) proteins (d) RNA

5-38 The process of sorting human chromosome pairs by size and morphology is called karyotyping. A modern method employed for karyotyping is called chromosome painting. How are individual chromosomes "painted"? (a) with a laser (b) using fluorescent antibodies (c) using fluorescent DNA molecules (d) using green fluorescent protein

5-52 Nucleosomes are formed when DNA wraps _____ times around the histone octamer in a ______ coil. (a) 2.0, right-handed (b) 2.5, left-handed (c) 1.7, left-handed (d) 1.3, right-handed

5-55 The core histones are small, basic proteins that have a globular domain at the C-terminus and a long, extended conformation at the N-terminus. Which of the following is not true of the N-terminal "tail" of these histones? (a) It is subject to covalent modifications (b) It extends out of the nucleosome core (c) It binds to DNA in a sequence-specific manner (d) It helps DNA pack tightly

Vesicles from the ER enter the Golgi at the ______. (a) medial cisternae. (b) trans Golgi network. (c) cis Golgi network. (d) trans cisternae.

True or false - Every stem cell gives rise to single type of progeny cell

False

5-6 You are a virologist interested in studying the evolution of viral genomes. You are studying two newly isolated viral strains and have sequenced their genomes. You find that the genome of strain 1 contains 25% A, 55% G, 20% C, and 10% T. You report that you have isolated a virus with a single-stranded DNA genome. Based on what evidence can you make this conclusion? (a) single-stranded genomes always have a large percentage of purines (b) using the formula: G - A = C + T (c) Double-stranded genomes have equal amounts of A and T (d) Single-stranded genomes have a higher rate of mutation

5-63 When there is a well-established segment of heterochromatin on an interphase chromosome, there is usually a special barrier sequence that prevents the heterochromatin from expanding along the entire chromosome. Gene A, which is normally expressed, has been moved by DNA recombination near an area of heterochromatin. None of the daughter cells produced after this recombination event express gene A, even though its DNA sequence is unchanged. What is the best way to describe what has happened to the function of gene A in these cells? (a) barrier destruction (b) heterochromatization (c) epigenetic inheritance (d) euchromatin depletion

5-66 How do changes in histone modifications lead to changes in chromatin structure? (a) They directly lead to changes in the positions of the core histones (b) They change the affinity between the histone octamer and the DNA (c) They help recruit other proteins to the chromatin (d) They cause the histone N-terminal tails to become hyperextended

Apoptosis differs from necrosis in that necrosis ________________. (a) requires the reception of an extracellular signal. (b) causes DNA to fragment. (c) causes cells to swell and burst, whereas apoptotic cells shrink and condense. (d) involves a caspase cascade.

Beside the distortion in the DNA backbone caused by a mismatched base pair, what additional mark is there on eukaryotic DNA to indicate which strand needs to be repaired? (a) a nick in the template strand (b) a chemical modification of the new strand (c) a nick in the new strand (d) a sequence gap in the new strand

DNA replication is considered semiconservative because ____________________________. (a) after many rounds of DNA replication, the original DNA double helix is still intact. (b) each daughter DNA molecule consists of two new strands copied from the parent DNA molecule. (c) each daughter DNA molecule consists of one strand from the parent DNA molecule and one new strand. (d) new DNA strands must be copied from a DNA template.

Figure Q15-48 (a) The oligosaccharide should have been added to the serine instead of the asparagine. (b) The oligosaccharide should have been added one sugar at a time. (c) The oligosaccharide needs to be further modified before it is mature. (d) The oligosaccharide needs a disulfide bond.

How does S-Cdk help guarantee that replication occurs only once during each cell cycle? (a) It blocks the rise of Cdc6 concentrations early in G1. (b) It phosphorylates and inactivates DNA helicase. (c) It phosphorylates the Cdc6 protein, marking it for destruction. (d) It promotes the assembly of a prereplicative complex.

In addition to the repair of DNA double-strand breaks, homologous recombination is a mechanism for generating genetic diversity by swapping segments of parental chromosomes. During which process does swapping occur? (a) DNA replication (b) DNA repair (c) meiosis (d) transposition

In which cellular location would you expect to find ribosomes translating mRNAs that encode ribosomal proteins? (a) the nucleus (b) on the rough ER (c) in the cytosol (d) in the lumen of the ER

Most proteins destined to enter the endoplasmic reticulum _________. (a) are transported across the membrane after their synthesis is complete. (b) are synthesized on free ribosomes in the cytosol. (c) begin to cross the membrane while still being synthesized. (d) remain within the endoplasmic reticulum.

Select the option that best completes the following statement: Nonhomologous end joining is a process by which a double-stranded DNA end is joined ___________________. (a) to a similar stretch of sequence on the complementary chromosome. (b) after repairing any mismatches. (c) to the nearest available double-stranded DNA end. (d) after filling in any lost nucleotides, helping to maintain the integrity of the DNA sequence.

Several members of the same family were diagnosed with the same kind of cancer when they were unusually young. Which one of the following is the most likely explanation for this phenomenon? It is possible that the individuals with the cancer have _______________________. (a) inherited a cancer-causing gene that suffered a mutation in an ancestor's somatic cells. (b) inherited a mutation in a gene required for DNA synthesis. (c) inherited a mutation in a gene required for mismatch repair. (d) inherited a mutation in a gene required for the synthesis of purine nucleotides.

Signal sequences that direct proteins to the correct compartment are _________. (a) added to proteins through post-translational modification. (b) added to a protein by a protein translocator. (c) encoded in the amino acid sequence and sufficient for targeting a protein to its correct destination. (d) always removed once a protein is at the correct destination.

Sometimes, chemical damage to DNA can occur just before DNA replication begins, not giving the repair system enough time to correct the error before the DNA is duplicated. This gives rise to mutation. If the adenosine in the sequence TCAT is depurinated and not repaired, which of the following is the point mutation you would observe after this segment has undergone two rounds of DNA replication? (a) TCGT (b) TAT (c) TCT (d) TGTT

The Retinoblastoma (Rb) protein blocks cells from entering the cell cycle by ______. (a) phosphorylating Cdk. (b) marking cyclins for destruction by proteolysis. (c) inhibiting cyclin transcription. (d) activating apoptosis.

The chromatin structure in eukaryotic cells is much more complicated than that observed in prokaryotic cells. This is thought to be the reason that DNA replication occurs much faster in prokaryotes. How much faster is it? (a) 2× (b) 5× (c) 10× (d) 100×

The concentration of mitotic cyclin (M cyclin) ________________. (a) rises markedly during M phase. (b) is activated by phosphorylation. (c) falls toward the end of M phase as a result of ubiquitylation and degradation. (d) is highest in G1 phase.

Which of the following descriptions is consistent with the behavior of a cell that lacks a protein required for a checkpoint mechanism that operates in G2? (a) The cell would be unable to enter M phase. (b) The cell would be unable to enter G2. (c) The cell would enter M phase under conditions when normal cells would not. (d) The cell would pass through M phase more slowly than normal cells

Which of the following organelles is not part of the endomembrane system? (a) Golgi apparatus (b) the nucleus (c) mitochondria (d) lysosomes

Which of the following statements about nuclear transport is true? (a) mRNAs and proteins transit the nucleus through different types of nuclear pores. (b) Nuclear import receptors bind to proteins in the cytosol and bring the proteins to the nuclear pores, where the proteins are released from the receptors into the pores for transit into the nucleus. (c) Nuclear pores have water-filled passages that small, water-soluble molecules can pass through in a nonselective fashion. (d) Nuclear pores are made up of many copies of a single protein.

Which of the following statements about the anaphase-promoting complex (APC) is false? (a) It promotes the degradation of proteins that regulate M phase. (b) It inhibits M-Cdk activity. (c) It is continuously active throughout the cell cycle. (d) M-Cdk stimulates its activity.

Which of the following statements about the unfolded protein response (UPR) is false? (a) Activation of the UPR results in the production of more ER membrane. (b) Activation of the UPR results in the production of more chaperone proteins. (c) Activation of the UPR occurs when receptors in the cytoplasm sense misfolded proteins. (d) Activation of the UPR results in the cytoplasmic activation of gene regulatory proteins.

Which of the following statements about vesicular membrane fusion is false? (a) Membrane fusion does not always immediately follow vesicle docking. (b) The hydrophilic surfaces of membranes have water molecules associated with them that must be displaced before vesicle fusion can occur. (c) The GTP hydrolysis of the Rab proteins provides the energy for membrane fusion. (d) The interactions of the v-SNAREs and the t-SNAREs pull the vesicle membrane and the target organelle membrane together so that their lipids can intermix.

Which of the following statements is true? (a) Proteins destined for the ER are translated by a special pool of ribosomes whose subunits are always associated with the outer ER membrane. (b) Proteins destined for the ER translocate their associated mRNAs into the ER lumen where they are translated. (c) Proteins destined for the ER are translated by cytosolic ribosomes and are targeted to the ER when a signal sequence emerges during translation. (d) Proteins destined for the ER are translated by a pool of cytosolic ribosomes that contain ER-targeting sequences that interact with ER-associated protein translocators.

Which of the following statements is true? (a) The signal sequences on mitochondrial proteins are usually at the C-terminus. (b) Most mitochondrial proteins are not imported from the cytosol but are synthesized inside the mitochondria. (c) Chaperone proteins in the mitochondria facilitate the movement of proteins across the outer and inner mitochondrial membranes. (d) Mitochondrial proteins cross the membrane in their native, folded state.

You engineer yeast cells that express the M cyclin during S phase by replacing the promoter sequence of the M cyclin gene with that of S cyclin. Keeping in mind that yeast cells have one common Cdk that binds to all cyclins, which of the following outcomes is least likely during this experiment? (a) There will be both M cyclin-Cdk and S cyclin-Cdk complexes in the cell during S phase. (b) Some substrates that are normally phosphorylated in M phase will now be phosphorylated in S phase. (c) G1 cyclins will be expressed during S phase. (d) S-Cdk targets will be phosphorylated during S phase.

Your friend has just joined a lab that studies vesicle budding from the Golgi and has been given a cell line that does not form mature vesicles. He wants to start designing some experiments but wasn't listening carefully when he was told about the molecular defect of this cell line. He's too embarrassed to ask and comes to you for help. He does recall that this coat proteins cell line forms coated pits but vesicle budding and the removal of don't happen. Which of the following proteins might be lacking in this cell line? (a) clathrin (b) Rab (c) dynamin (d) adaptin

Your friend works in a biotechnology company and has discovered a drug that blocks the ability of Ran to exchange GDP for GTP. What is the most likely effect of this drug on nuclear transport? (a) Nuclear transport receptors would be unable to bind cargo. (b) Nuclear transport receptors would be unable to enter the nucleus. (c) Nuclear transport receptors would be unable to release their cargo in the nucleus. (d) Nuclear transport receptors would interact irreversibly with the nuclear pore fibrils.

Match the type of intermediate filament with its appropriate location. lamins _________ A. nerve cells neurofilaments _________ B. epithelia vimentins _________ C. nucleus keratins _________ D. connective tissue

C A B D

Will panels C and D be faithfully transmitted during cell division?

C will be segregated to progeny properly D will not be because one product has 2 centromeres that will cause severe damage to it during mitosis and the other product does not have one at all and will cause the chromosome to be rapidly lost

Which of the following statements about gap junctions is false? A) Gap junctions are made of connexons. B) Molecules up to 1000 daltons in molecular weight can move across gap junctions. C) Because gap junctions do not allow ions to pass through, they are not used for electrically coupling cells. D) Gap junctions can close in response to extracellular signals.

C) Because gap junctions do now allow ions to pass through, they are not used for electrically coupling cells.

A fibroblast can attach indirectly to collagen via which type of protein? A) Proteoglycan B) Cadherin C) Fibronectin D) Integrin

C) Fibronectin

Which of the following epithelial cell junctions is not involved in providing mechanical strength to an epithelial sheet? A) Adherens junctions B) Desmosomes C) Gap junctions

C) Gap junctions

5-24 The complete set of information found in a given organism's DNA is called its ____________. (a) genetic code (b) coding sequence (c) gene (d) genome

Which of the following is NOT true of integrin? A) When integrin binds to the extracellular matrix, it stretches into an extended, activated state to attach to molecules on the inside of the cell. B) Certain intracellular chemical signals can activate integrins from inside the cell, causing them to reach out and grab hold of extracellular structures. C) Integrin molecules are always activated and serve as stable anchor with two sticky ends.

C) Integrin molecules are always activated and serve as stable anchor with two sticky ends

Which of the following statements is false? A) Proteoglycans can act as filters to regulate which molecules pass through the extracellular medium. B) The negative charge associated with proteoglycans attracts cations, which cause water to be sucked into the extracellular matrix. C) Proteoglycans are a major component of compact connective tissues but are relatively unimportant in watery tissues such as the jellylike substance in the interior of the eye. D) Glycosaminoglycans are components of proteoglycan.

C) Proteoglycans are a major component of compact connective tissues but are relatively unimportant in watery tissues such as the jellylike substance in the interior of the eye.

Which of the following determines the direction that cellulose is laid down in the extracellular space of a plant cell? A) The amount of turgor pressure within a cell B) The availability of sugar monomers for cellulose elongation C) The orientation of microtubules on the cytoplasmic side of the plasma membrane

C) The orientation of microtubules on the cytoplasmic side of the plasma membrane

Which epithelial cell junctions serve to seal neighboring cells together so that water-soluble molecules cannot easily leak between them? A) Desmosomes B) Gap junctions C) Tight junctions D) Adherens junctions

C) Tight junctions

Which of the following statements about cancer is false? A) Viruses cause some cancers. B) Tobacco use is responsible for more than 20% of all cancer deaths. C) A mutation in even a single cancer-critical gene is sufficient to convert a normal cell into a cancer cell. D) Chemical carcinogens cause cancer by changing the nucleotide sequence of DNA.

C) a mutation in even a single cancer-critical gene is sufficient to convert a normal cell into a cancer cell

Tight junctions ______________________. A) allow small water-soluble molecules to pass from cell to cell B) interact with the intermediate filaments inside the cell C) are formed from claudins and occludins D) are found in cells in connective tissues

C) are formed from claudins and occludins

An adult hemopoietic stem cell found in the bone marrow ______________________. A) will occasionally produce epidermal cells when necessary B) can produce only red blood cells C) can undergo self-renewing divisions for the lifetime of a healthy animal D) will express all the same transcription factors as those found in an unfertilized egg

C) can undergo self-renewing divisions for the lifetime of a healthy animal

Which of the following molecules are not found in plants? A) cellulose B) lignin C) collagen D) pectin

C) collagen

Therapeutic cloning is used to: A) fix mutant genes. B) breed premium livestock. C) generate embryonic stem cells. D) create embryos for IVF

C) generate embryonic stem cells

Which of the following statements about the cytoskeleton is false? (a) The cytoskeleton is made up of three types of protein filament. (b) The bacterial cytoskeleton is important for cell division and DNA segregation. (c) Protein monomers that are held together with covalent bonds form cytoskeletal filaments. (d) The cytoskeleton of a cell can change in response to the environment.

C) protein monomers that are held together with covalent bonds form cytoskeletal filaments

Which type of junction contributes the most to the polarization of epithelial cells? A) adherens junctions B) desmosomes C) tight junctions D) gap junctions

C) tight junctions

Two mutations are needed to inactivate which class of cancer causing gene? A) Proto-oncogene B) Oncogene C) Tumor suppressor gene

C) tumor suppressor gene

Actin-binding proteins bind to actin and can modify its properties. You purify a protein, Cap1, that seems to bind and cap one end of an actin filament, although you do not know whether it binds the plus end or the minus end. To determine which end of the actin filament your protein binds to, you decide to examine the effect of Cap1 on actin polymerization by measuring the kinetics of actin filament formation in the presence and the absence of Cap1 protein. You obtain the following results (see Figure Q17-36). Do you think Cap1 binds the plus end or the minus end of actin? Explain your reasoning.

Cap1 binds the plus end of actin, because it seems to inhibit actin polymerization. Actin filaments grow through the addition of monomers to the plus end of the actin filament. A capping protein that binds the plus end of actin can block monomer addition to the actin filament. Thus, less actin polymerization will be seen in the presence of the Cap1 protein.

5-34 The human genome is divided into linear segments and packaged into structures called chromosomes. What is the total number of chromosomes found in each of the somatic cells in your body? (a) 22 (b) 23 (c) 44 (d) 46

Duplication and divergence

Consider a gene with a particular function. Mutation X and mutation Y each cause defects in the function of the encoded protein, yet a gene containing both mutations X and Y encodes a protein that works even better than the original protein. The odds are exceedingly small that a single mutational event will generate both mutations X and Y. Explain a simple way that an organism with a mutant gene containing both mutations X and Y could arise during evolution.

10-15 You are interested in a single-stranded DNA molecule that contains the following sequence:Which molecule can be used as a probe that will hybridize to your sequence of interest? (a) 5′-GATTGCAT-3′ (b) 5′-TACGTTAG-3′ (c) 5′-CTAACGTA-3′ (d) 5′-ATGCAATC-3′

10-18 DNA ligase is an enzyme used when making recombinant DNA molecules in the lab. In what normal cellular process is DNA ligase involved? (a) none, it is only found in virally infected cells (b) transcription (c) transformation (d) DNA replication

10-21 DNA can be introduced into bacteria by a mechanism called ____________. (a) transcription. (b) ligation. (c) replication. (d) transformation.

10-28 A DNA library has been constructed by purifying chromosomal DNA from mice, cutting the DNA with the restriction enzyme NotI, and inserting the fragments into the NotI site of a plasmid vector. What information cannot be retrieved from this library? (a) gene regulatory sequences (b) intron sequences (c) sequences of the telomeres (the ends of the chromosomes) (d) amino acid sequences of proteins

10-29 You want to design a DNA probe used for hybridization to isolate a clone from a cDNA library. Which of the following concerns about DNA probe design is the most legitimate? (a) You must be careful when designing your probe to take into account which DNA strand was transcribed in mRNA and choose a probe complementary to the mRNA. (b) You must be careful not to include any DNA sequences in your probe that are upstream (5′) of the AUG start codon. (c) You must make sure that all the DNA sequences in your probe lie within an exon, and do not span two exons. (d) You must make sure that all the DNA sequences in your probe are not located downstream (3′) of the polyadenylation signal.

10-41 PCR involves a heating step, followed by a cooling step, and then DNA synthesis. What is the primary reason for why this cooling step is necessary? (a) Cooling the reaction ensures the integrity of the covalent bonds holding the nucleotides together in the DNA strand. (b) Cooling the reaction gives the DNA polymerase an opportunity to rest from the previous cycle so that it will be ready for the next round of synthesis. (c) Transcription takes place during the cooling step. (d) Cooling the reaction brings the temperature down to a level that is compatible with the short primers forming stable hydrogen bonds with the DNA to be amplified.

10-50 You have sequenced a fragment of DNA and produced the gel shown in Figure Q10-50. Near the top of the gel, there is a section where there are bands in all four lanes (indicated by the arrow). Which of the following mishaps would account for this phenomenon? Explain your answer.(a) You mistakenly added all four dideoxynucleotides to one of the reactions. (b) You forgot to add deoxynucleotides to the reactions. (c) Your primer hybridizes to more than one area of the fragment of DNA you are sequencing. (d) A restriction nuclease cut a fraction of the DNA you are sequencing.

10-52 Second-generation sequencing differs from Sanger sequencing because _____________. (a) second-generation sequencing does not depend on chain-terminator ddNTPs. (b) second-generation sequencing does not require DNA polymerase. (c) for the cost per base sequenced, second-generation sequencing is much more expensive than Sanger sequencing. (d) second-generation sequencing can sequence tens of millions of pieces of DNA at the same time on a single glass slide.

10-57 You have been hired to create a cat that will not cause allergic reactions in cat-lovers. Your coworkers have cloned the gene encoding a protein found in cat saliva, expressed the protein in bacteria, and shown that it causes violent allergic reactions in people. But you soon realize that even if you succeed in making a knockout cat lacking this gene, anyone who buys one will easily be able to make more hypoallergenic cats just by breeding them. Which of the following will ensure that people will always have to buy their hypoallergenic cats from you? (a) Inject the modified embryonic stem (ES) cells into embryos that have a genetic defect to prevent the mature adult from reproducing. (b) Implant the injected embryos into a female cat that is sterile as a result of a genetic defect. (c) Sell only the offspring from the first litter of the female cat implanted with the injected embryos. (d) Surgically remove the sexual organs of all the knockouts before you sell them.

10-6 You have a piece of circular DNA that can be cut by the restriction nucleases EcoRI, HindIII, and NotI, as indicated in Figure Q10-6.Which of the following statements is false? (a) One piece of DNA will be obtained when this DNA is cut by NotI. (b) A piece of DNA that cannot be cut by EcoRI will be obtained by cutting this DNA with both NotI and HindIII. (c) Two DNA fragments that cannot be cut by HindIII will be obtained when this DNA is cut by EcoRI and NotI. (d) Two DNA fragments of unequal size will be created when this DNA is cut by both HindIII and EcoRI.

5-12 Hershey and Chase used radiolabeled macromolecules to identify the material that contains heritable information. What radioactive material was used to track DNA during this experiment? (a) 3H (b) 14C (c) 35S (d) 32P

5-13 Which of the following chemical groups is not used to construct a DNA molecule? (a) five-carbon sugar (b) phosphate (c) nitrogen-containing base (d) six-carbon sugar

5-15 Which of the following DNA strands can form a DNA duplex by pairing with itself at each position? (a) 5′-AAGCCGAA-3′ (b) 5′-AAGCCGTT-3′ (c) 5′-AAGCGCAA-3′ (d) 5′-AAGCGCTT-3′

5-4 In the 1940s, proteins were thought to be the more likely molecules to house genetic information. What was the primary reason that DNA was not originally believed to be the genetic material? (a) DNA has a high density of negative charges (b) Nucleotides were known to be a source of chemical energy for the cell (c) Both protein and nucleic acids were found to be components of chromosomes (d) DNA was found to contain only four different chemical building blocks

5-41 Which of the following questions would not be answered by using karyotyping? (a) Is the individual genetically female or male? (b) Do any of the chromosomes contain pieces that belong to other chromosomes? (c) Does the individual have an extra chromosome? (d) Do any chromosomes contain point mutations?

5-5 In a DNA double helix, _____________________. (a) the two DNA strands are identical. (b) purines pair with purines. (c) thymine pairs with cytosine. (d) the two DNA strands run antiparallel.

5-54 The octameric histone core is composed of four different histone proteins, assembled in a stepwise manner. Once the core octamer has been formed, DNA wraps around it to form a nucleosome core particle. Which of the following histone proteins does not form part of the octameric core? (a) H4 (b) H2A (c) H3 (d) H1

5-69 The inactivation of one X chromosome is established by the directed spreading of heterochromatin. The silent state of this chromosome is _______________ in the subsequent cell divisions. (a) completed (b) switched (c) erased (d) maintained

5-9 Several experiments were required to demonstrate how traits are inherited. Which scientist or team of scientists obtained definitive results demonstrating that DNA is the genetic molecule? (a) Griffith (b) Watson (c) Crick (d) Hershey and Chase

A molecule of bacterial DNA introduced into a yeast cell is imported into the nucleus but fails to replicate with the yeast DNA. Where do you think the block to replication arises? Choose the protein or protein complex below that is most probably responsible for the failure to replicate bacterial DNA. Give an explanation for your answer. (a) primase (b) helicase (c) DNA polymerase (d) initiator proteins

After isolating the rough endoplasmic reticulum from the rest of the cytoplasm, you purify the RNAs attached to it. Which of the following proteins do you expect the RNA from the rough endoplasmic reticulum to encode? (a) soluble secreted proteins (b) ER membrane proteins (c) plasma membrane proteins (d) all of the above

Different glycoproteins can have a diverse array of oligosaccharides. Which of the statements below about this diversity is true? (a) Extensive modification of oligosaccharides occurs in the extracellular space. (b) Different oligosaccharides are covalently linked to proteins in the ER and the Golgi. (c) A diversity of oligosaccharyl transferases recognizes specific protein sequences, resulting in the linkage of a variety of oligosaccharides to proteins. (d) Oligosaccharide diversity comes from modifications that occur in the ER and the Golgi of the 14-sugar oligosaccharide added to the protein in the ER.

Disassembly of the nuclear envelope ________________. (a) causes the inner nuclear membrane to separate from the outer nuclear membrane. (b) results in the conversion of the nuclear envelope into protein-free membrane vesicles. (c) is triggered by the phosphorylation of integrins. (d) must occur for kinetochore microtubules to form in animal cells.

Even though DNA polymerase has a proofreading function, it still introduces errors in the newly synthesized strand at a rate of 1 per 107 nucleotides. To what degree does the mismatch repair system decrease the error rate arising from DNA replication? (a) 2-fold (b) 5-fold (c) 10-fold (d) 100-fold

How does the total number of replication origins in bacterial cells compare with the number of origins in human cells? (a) 1 versus 100 (b) 5 versus 500 (c) 10 versus 1000 (d) 1 versus 10,000

Human beings with the inherited disease xeroderma pigmentosum have serious problems with lesions on their skin and often develop skin cancer with repeated exposure to sunlight. What type of DNA damage is not being recognized in the cells of these individuals? (a) chemical damage (b) X-ray irradiation damage (c) mismatched bases (d) ultraviolet irradiation damage

If the genome of the bacterium E. coli requires about 20 minutes to replicate itself, how can the genome of the fruit fly Drosophila be replicated in only 3 minutes? (a) The Drosophila genome is smaller than the E. coli genome. (b) Eukaryotic DNA polymerase synthesizes DNA at a much faster rate than prokaryotic DNA polymerase. (c) The nuclear membrane keeps the Drosophila DNA concentrated in one place in the cell, which increases the rate of polymerization. (d) Drosophila DNA contains more origins of replication than E. coli DNA.

In which phase of the cell cycle do cells check to determine whether the DNA is fully and correctly replicated? (a) at the transition between G1 and S (b) when cells enter G0 (c) during M (d) at the end of G2

Levels of Cdk activity change during the cell cycle, in part because ________________. (a) the Cdks phosphorylate each other. (b) the Cdks activate the cyclins. (c) Cdk degradation precedes entry into the next phase of the cell cycle. (d) cyclin levels change during the cycle.

MPF activity was discovered when cytoplasm from a Xenopus M-phase cell was injected into Xenopus oocytes, inducing the oocytes to form a mitotic spindle. In a control experiment, Xenopus interphase cytoplasm was injected into oocytes and shown not to induce the formation of a mitotic spindle. Which of the following statements is not a legitimate conclusion from the control experiment? (a) The piercing of the oocyte membrane by a needle is insufficient to cause mitotic spindle formation. (b) An increased volume of cytoplasm is insufficient to cause mitotic spindle formation. (c) Injection of extra RNA molecules is insufficient to cause mitotic spindle formation. (d) Components of an interphase nucleus are insufficient to cause mitotic spindle formation.

N-linked oligosaccharides on secreted glycoproteins are attached to ________. (a) nitrogen atoms in the polypeptide backbone. (b) the serine or threonine in the sequence Asn-X-Ser/Thr. (c) the N-terminus of the protein. (d) the asparagine in the sequence Asn-X-Ser/Thr.

T/F: The low cytosolic Ca2+ concentration sensitizes the cell to an influx of Ca2+, ensuring a rapid response to environmental stimuli.

True

Telomeres serve as caps at the ends of linear chromosomes. Which of the following is not true regarding the replication of telomeric sequences? (a) The lagging-strand telomeres are not completely replicated by DNA polymerase. (b) Telomeres are made of repeating sequences. (c) Additional repeated sequences are added to the template strand. (d) The leading strand doubles back on itself to form a primer for the lagging strand.

The G1 DNA damage checkpoint ________________. (a) causes cells to proceed through S phase more quickly. (b) involves the degradation of p53. (c) is activated by errors caused during DNA replication. (d) involves the inhibition of cyclin-Cdk complexes by p21.

The events listed below are all necessary for homologous recombination to occur properly: A. Holliday junction cut and ligated B. strand invasion C. DNA synthesis D. DNA ligation E. double-strand break F. nucleases create uneven strands Which of the following is the correct order of events during homologous recombination? (a) E, B, F, D, C, A (b) B, E, F, D, C, A (c) C, E, F, B, D, A (d) E, F, B, C, D, A

What part of the DNA replication process would be most directly affected if a strain of bacteria lacking DNA ligase were used to make the cell extracts? (a) initiation of DNA synthesis (b) Okazaki fragment synthesis (c) leading-strand elongation (d) lagging-strand completion

What part of the DNA replication process would be most directly affected if a strain of bacteria lacking the exonuclease activity of DNA polymerase were used to make the cell extracts? (a) initiation of DNA synthesis (b) Okazaki fragment synthesis (c) leading-strand elongation (d) lagging-strand completion

What would be the most obvious outcome of repeated cell cycles consisting of S phase and M phase only? (a) Cells would not be able to replicate their DNA. (b) The mitotic spindle could not assemble. (c) Cells would get larger and larger. (d) The cells produced would get smaller and smaller.

When introduced into mitotic cells, which of the following is expected to impair anaphase B but not anaphase A? (a) an antibody against myosin (b) ATPγS, a nonhydrolyzable ATP analog that binds to and inhibits ATPases (c) an antibody against the motor proteins that move from the plus end of microtubules to the minus end (d) an antibody against the motor proteins that move from the minus end of microtubules toward the plus end

Where are proteins in the chloroplast synthesized? (a) in the cytosol (b) in the chloroplast (c) on the endoplasmic reticulum (d) in both the cytosol and the chloroplast

Which of the following choices reflects the appropriate order of locations through which a protein destined for the plasma membrane travels? (a) lysosome ◊ endosome ◊ plasma membrane (b) ER ◊lysosome ◊plasma membrane (c) Golgi ◊ lysosome ◊ plasma membrane (d) ER ◊ Golgi ◊ plasma membrane

Which of the following is not good direct evidence that the cell-cycle control system is conserved through billions of years of divergent evolution? (a) A yeast cell lacking a Cdk function can use the human Cdk to substitute for its missing Cdk during the cell cycle. (b) The amino acid sequences of cyclins in plants are similar to the amino acid sequences of cyclins in humans. (c) The Cdk proteins in humans share conserved phosphorylation sites with the Cdk proteins in yeast. (d) Yeast cells have only one Cdk, whereas humans have many Cdks.

Which of the following protein families are not involved in directing transport vesicles to the target membrane? (a) SNAREs (b) Rabs (c) tethering proteins (d) adaptins

Which of the following statements about a protein in the lumen of the ER is false? (a) A protein in the lumen of the ER is synthesized by ribosomes on the ER membrane. (b) Some of the proteins in the lumen of the ER can end up in the extracellular space. (c) Some of the proteins in the lumen of the ER can end up in the lumen of an organelle in the endomembrane system. (d) Some of the proteins in the lumen of the ER can end up in the plasma membrane.

Which of the following statements about apoptosis is true? (a) Cells that constitutively express Bcl2 will be more prone to undergo apoptosis. (b) The prodomain of procaspases contains the catalytic activity necessary for procaspase activation. (c) Bax and Bak promote apoptosis by binding to procaspases in the apoptosome. (d) Apoptosis is promoted by the release of cytochrome c into the cytosol from mitochondria.

Which of the following statements about disulfide bond formation is false? (a) Disulfide bonds do not form under reducing environments. (b) Disulfide bonding occurs by the oxidation of pairs of cysteine side chains on the protein. (c) Disulfide bonding stabilizes the structure of proteins. (d) Disulfide bonds form spontaneously within the ER because the lumen of the ER is oxidizing.

Which of the following statements about the newly synthesized strand of a human chromosome is true? (a) It was synthesized from a single origin solely by continuous DNA synthesis. (b) It was synthesized from a single origin by a mixture of continuous and discontinuous DNA synthesis. (c) It was synthesized from multiple origins solely by discontinuous DNA synthesis. (d) It was synthesized from multiple origins by a mixture of continuous and discontinuous DNA synthesis.

Which of the following statements correctly explains what it means for DNA replication to be bidirectional? (a) The replication fork can open or close, depending on the conditions. (b) The DNA replication machinery can move in either direction on the template strand. (c) Replication-fork movement can switch directions when the fork converges on another replication fork. (d) The replication forks formed at the origin move in opposite directions.

Which of the following statements is false? (a) Cytokinesis in plant cells is mediated by the microtubule cytoskeleton. (b) Small membrane vesicles derived from the Golgi apparatus deliver new cell-wall material for the new wall of the dividing cell. (c) The phragmoplast forms from the remains of interpolar microtubules of the mitotic spindle. (d) Motor proteins walking along the cytoskeleton are important for the contractile ring that guides formation of the new cell wall.

True or false? To meet a challenge or develop a new function, evolution essentially builds from first principles designing from scratch to find the best possible solution

False

Which of the following statements is false? (a) Mitotic Cdk must be phosphorylated by an activating kinase (Cak) before it is active. (b) Phosphorylation of mitotic Cdk by the inhibitory kinase (Wee1) makes the Cdk inactive, even if it is phosphorylated by the activating kinase. (c) Active M-Cdk phosphorylates the activating phosphatase (Cdc25) in a positive feedback loop. (d) The activating phosphatase (Cdc25) removes all phosphates from mitotic Cdk so that M-Cdk will be active.

Which of the following statements is false? (a) The cleavage furrow is a puckering of the plasma membrane caused by the constriction of a ring of filaments attached to the plasma membrane. (b) The cleavage furrow will not begin to form in the absence of a mitotic spindle. (c) The cleavage furrow always forms perpendicular to the interpolar microtubules. (d) The cleavage furrow always forms in the middle of the cell.

Which of the following statements is true? (a) Anaphase A must be completed before anaphase B can take place. (b) In cells in which anaphase B predominates, the spindle will elongate much less than in cells in which anaphase A dominates. (c) In anaphase A, both kinetochore and interpolar microtubules shorten. (d) In anaphase B, microtubules associated with the cell cortex shorten.

You are examining the DNA sequences that code for the enzyme phosphofructokinase in skinks and Komodo dragons. You notice that the coding sequence that actually directs the sequence of amino acids in the enzyme is very similar in the two organisms but that the surrounding sequences vary quite a bit. What is the most likely explanation for this? (a) Coding sequences are repaired more efficiently. (b) Coding sequences are replicated more accurately. (c) Coding sequences are packaged more tightly in the chromosomes to protect them from DNA damage. (d) Mutations in coding sequences are more likely to be deleterious to the organism than mutations in noncoding sequences.

You are interested in Fuzzy, a soluble protein that functions within the ER lumen. Given that information, which of the following statements must be true? (a) Fuzzy has a C-terminal signal sequence that binds to SRP. (b) Only one ribosome can be bound to the mRNA encoding Fuzzy during translation. (c) Fuzzy must contain a hydrophobic stop-transfer sequence. (d) Once the signal sequence from Fuzzy has been cleaved, the signal peptide will be ejected into the ER membrane and degraded.

You have discovered an "Exo-" mutant form of DNA polymerase in which the 3′- to-5′ exonuclease function has been destroyed but the ability to join nucleotides together is unchanged. Which of the following properties do you expect the mutant polymerase to have? (a) It will polymerize in both the 5′-to-3′ direction and the 3′-to-5′ direction. (b) It will polymerize more slowly than the normal Exo+ polymerase. (c) It will fall off the template more frequently than the normal Exo+ polymerase. (d) It will be more likely to generate mismatched base pairs.

Which type of epithelial junction plays a role in an epithelial sheet's ability to develop tension or change its shape by contraction? A) Desmosome B) Gap junction C) Tight junction D) Adherens junction

D) Adherens junction

How do reproductive cloning and therapeutic cloning differ? A) The DNA in the nucleus of cells produced for therapeutic cloning is genetically identical to the donor genome, whereas in cells produced for reproductive cloning it is not. B) Reproductive cloning requires a supply of fertilized donor egg cells, whereas therapeutic cloning requires unfertilized egg cells. C) Therapeutic cloning requires nuclear transplantation, whereas reproductive cloning does not. D) Embryos are placed into foster mothers during reproductive cloning but not during therapeutic cloning

D) Embryos are placed into foster mothers during reproductive cloning but not during therapeutic cloning

Which protein in a fibroblast's plasma membrane attaches to the extracellular matrix on the outside of the cell and (through adapter molecules) to actin inside the cell? A) Proteoglycan B) Cadherin C) Fibronectin D) Integrin

D) Integrin

How many mutations are required for a normal cell to turn into a cancer cell? A) 1 B) 2 C) 3 D) More than 3

D) More than 3

In the extracellular matrix of animal tissues, which of the following molecules allows the matrix to resist compression? A) Integrin B) Collagen C) Fibronectin D) Proteoglycans

D) Proteoglycans

Which of the following statements about animal connective tissues is true? A) Enzymes embedded in the plasma membrane synthesize the collagen in the extracellular matrix extracellularly. B) In connective tissue, the intermediate filaments within the cells are important for carrying the mechanical load. C) Cells can attach to a collagen matrix by using fibronectin, an integral membrane protein. D) Proteoglycans can resist compression in the extracellular matrix.

D) Proteoglycans can resist compression in the extracellular matrix

Which of the following is NOT a key behavior of cancer cells? A) They have a reduced dependence on signals from other cells for their growth, survival, and division. B) They are less prone than normal cells to kill themselves by apoptosis. C) They can often proliferate indefinitely. D) Most are genetically unstable, with a greatly increased mutation rate. E) They are abnormally invasive. D) They digest neighboring cells to fuel proliferation. F) They can often survive and proliferate in foreign tissues to form secondary tumors

D) They digest neighboring cells to fuel proliferation

Which of the following statements about the cytoskeleton is true? (a) All eucaryotic cells have actin, microtubules, and intermediate filaments in their cytoplasm. (b) The cytoskeleton provides a rigid and unchangeable structure important for the shape of the cell. (c) The three cytoskeletal filaments perform distinct tasks in the cell and act completely independently of one another. (d) Actin filaments and microtubules have an inherent polarity, with a plus end that grows more quickly than the minus end.

D) actin filaments and microtubules have an inherent polarity, with a plus end that grows more quickly than the minus end

Hemidesmosomes are important for ______________________. A) tubulation of epithelial sheets B) linkages to glycosaminoglycans C) forming the basal lamina D) attaching epithelial cells to the extracellular matrix

D) attaching epithelial cells to the extracellular matrix

T/F: The electron-transport proteins, utilized in stage 1 of photosynthesis, reside in the inner membrane of the chloroplast

False (The electron-transport system in chloroplasts resides in the thylakoid membrane)

Mouse embryonic stem (ES) cells ______________________. A) can only be produced through therapeutic cloning B) can give rise to all tissues and cell types in the body except germ cells C) can be implanted in foster mothers to produce cloned cows and other animals D) come from the inner cell mass of early embryos

D) come from the inner cell mass of early embryos

Which of the statements below about intermediate filaments is false? (a) They can stay intact in cells treated with concentrated salt solutions. (b) They can be found in the cytoplasm and the nucleus. (c) They can be anchored to the plasma membrane at cell-cell junction. (d) Each filament is about 10 μm in diameter.

D) each filament is about 10 μm in diameter

A malignant tumor is more dangerous than a benign tumor because ______________________. A) its cells are proliferating faster B) it causes neighboring cells to mutate C) its cells attack and phagocytose neighboring normal tissue cells D) its cells invade other tissues

D) its cells invade other tissues

Fibroblasts organize the collagen of the extracellular matrix by ______________. A) cutting and rejoining the fibrils B) processing procollagen into collagen C) twisting fibrils together to make ropelike fibers D) pulling the collagen into sheets or cables after it has been secreted

D) pulling the collagen into sheets or cables after it has been secreted

Both multicellular plants and animals have _____________________. A) cells capable of locomotion B) cells with cell walls C) a cytoskeleton composed of actin filaments, microtubules, and intermediate filaments D) tissues composed of multiple different cell types

D) tissues composed of multiple different cell types

Do you agree or disagree with this statement? Explain your answer. Minus end-directed microtubule motors (like dyneins) deliver their cargo to the periphery of the cell, whereas plus end-directed microtubule motors (like kinesins) deliver their cargo to the interior of the cell.

Disagree. Plus end directed motors transport cargo to the cell periphery and minus end directed motors can be used for cargo delivery to the center of the cell. The centrosome established the principal array of microtubules in most animal cells, it nucleates microtubule growth at the minus end. Thus, the plus ends of the microtubules are near the PM and the minus ends are buried in the centrosome.

Do you agree or disagree with the following statement? Explain your answer. When skeletal muscle receives a signal from the nervous system to contract, the signal from the motor neuron triggers the opening of a voltage-sensitive Ca2+ channel in the muscle cells' plasma membrane, allowing Ca2+ to flow into the cell.

Disagree: this is describing cardiac muscle. The increase in IC Ca2+ during skeletal muscle contraction comes from an intracellular source. The Ca2+ is released from the lumen of the sarcoplasmic reticulum which is a specialized region of ER inside a muscle cell. The signal from the nerve terminaltriggers an AP in the muscle cell PM which causes a colatege sensitive membrane protein in the membranous transverse tubules to open a Ca2+ release chanel in the membrane of the sarcoplasmic reticulum.

T or F? Introns and transposons tend to slow the evolution of new genes.

False they can act as sites where recombinational crossovers occur and transposons also catalyze genetic rearrangements

Describe a mechanism that might drive evolution toward more or larger introns and could account for the introns late hypothesis.

Exon shuffling and acquisition of intron sequences as binding sites for crossovers

You isolate some muscle fibers to examine what regulates muscle contraction. When you bathe the muscle fibers in a solution containing ATP and Ca2+, you see muscle contraction (experiment 3 in Table Q17-49). Ca2+ is necessary, as solutions containing ATP alone or nothing do not stimulate contraction and thus the muscle remains in a relaxed state (experiments 1 and 2 in Table Q17-49). From what you know about the mechanism of muscle contraction, fill in your predictions of whether the muscle will be contracted or relaxed for experiments 4, 5, and 6. Explain your answers.

Experiment 4: RELAXED: troponin will not be able to bind Ca2+ so troponin can't undergo the conformational change the causes tropomyosin to alter its association with actin. This altered association is normally required for myosin to bind to actin. Experiment 5: CONTRACT: tropomyosin cannot bind to actin which means that myosin can. The presence of ATP means that it will be available for myosin to hydrolyze, causing contraction. Experiment 6: RELAXED: presence of Ca2+ will induce conformational change in troponin so tropomyosin will shift for actin to bind to myosin, but the myosin molecule will attach and then release because the myosin will ind the nonhydrolyzable analog of ATP. No hydrolysis can occur- relaxed.

Which of the following can give rise to cancer causing mutations? A) Tobacco smoke B) Ionizing radiation C) Sunlight D) Mistakes in DNA replication E) A and B F) All of the above

F) All of the above

T/F: Action potentials are usually mediated by voltage-gated Ca2+ channels.

False

T/F: Activated carrier molecules store heat energy for the cell to use later.

False

T/F: Aquaporin channels are found in the plasma membrane, and allow the rapid passage of water molecules and small ions in and out of cells

False

T/F: Brown fat cells make less ATP because they have an inefficient ATP synthase.

False

T/F: Catabolism is a general term that refers to the processes by which large molecules are synthesized from smaller molecules

False

T/F: Cytosolic Ca2+ concentration is kept low by the use of chelators such as EDTA.

False

T/F: During glycolysis, glucose molecules are broken down to yield CO2 and H2O.

False

T/F: Each round of the Calvin cycle uses five molecules of CO2 to produce one molecule of glyceraldehyde 3-phosphate and one of pyruvate

False

T/F: Facilitated diffusion can be described as the favorable movement of one solute down its concentration gradient being coupled with the unfavorable movement of a second solute up its concentration gradient

False

T/F: Gap junctions are large pores that connect the cytosol to the extracellular space

False

T/F: Gluconeogenesis is a linear reaction pathway that the cell employs to generate glucose from pyruvate and is exactly the reverse of the reactions in the glycolytic pathway.

False

T/F: Glycogen phosphorylase cleaves glucose monomers from the glycogen polymer, phosphorylating them at the same time so that they can be fed unchanged into the glycolytic pathway

False

T/F: Similar to oxidative phosphorylation, the electrons passed along the chloroplast electron-transport chain are ultimately passed on to a molecule of O2, to produce H2O.

False

T/F: The cleavage of fructose 1,6-bisphosphate yields two molecules of glyceraldehyde 3-phosphate.

False

T/F: The dark reactions of photosynthesis occur only in the absence of light

False

T/F: The differences in permeability between artificial lipid bilayers and cell membranes arise from variations in phospholipid content.

False

T/F: The driving force that pulls protons into the matrix is called the protonmotive force, which is a combination of the large force due to the pH gradient and the smaller force that results from the voltage gradient across the inner mitochondrial membrane.

False

T/F: The inner mitochondrial membrane contains porins, which allow pyruvate to enter for use in the citric acid cycle.

False

T/F: The inner mitochondrial membrane is actually a series of discrete, flattened, membrane-enclosed compartments called cristae, similar to what is seen in the Golgi apparatus.

False

T/F: The ion selectivity of a channel depends solely on the charge of the amino acids lining the pore inside the channel.

False

T/F: The net negative charge on the cytosolic side of the membrane enhances the rate of glucose import into the cell by a uniporter.

False

T/F: The primary mechanism by which Ca2+ acts as a signaling molecule is by increasing the net charge in the cytosol.

False

T or F? All highly conserved stretches of DNA in the genome are transcribed into RNA.

False, many are not transcribed and contain information for regulation of gene expression

Before chromosomes segregate in M phase, they and the segregation machinery must be appropriately prepared. Indicate whether the following statements are true or false Cohesins are required to make the chromosomes more compact and thus to prevent tangling between different chromosomes.

False. Condensins are required to make the chromosomes more compact and thus to prevent tangling between different chromosomes.

Before chromosomes segregate in M phase, they and the segregation machinery must be appropriately prepared. Indicate whether the following statements are true or false Sister chromatids are held together by condensins from the time they arise by DNA replication until the time they separate at anaphase.

False. Sister chromatids are held together by cohesins from the time they arise by DNA replication until the time they separate at anaphase.

Are the statements below true or false? Explain your answer. Statement 2: Therefore, the cell-cycle control system operates primarily by a timing mechanism, in which the entry into one phase starts a timer set for sufficient time to complete the required tasks. After a given amount of time has elapsed, a molecular "alarm" triggers movement to the next phase.

False. The cell-cycle control system does use a timing mechanism of sorts, but it also employs various surveillance and feedback mechanisms (checkpoints). Cells will not embark on later events or phases until the earlier events or phases have been completed successfully. In response to a defect or a delay in a cell-cycle event, cells engage molecular brakes to arrest the progression of the cell cycle at various checkpoints, to allow time for completion or repair.

Before chromosomes segregate in M phase, they and the segregation machinery must be appropriately prepared. Indicate whether the following statements are true or false The centromere nucleates a radial array of microtubules called an aster, and its duplication is triggered by S-Cdk.

False. The centrosome nucleates a radial array of microtubules called an aster, and its duplication is triggered by S-Cdk.

Before chromosomes segregate in M phase, they and the segregation machinery must be appropriately prepared. Indicate whether the following statements are true or false. The mitotic spindle is composed of actin filaments and myosin filaments

False. The contractile ring is composed of actin filaments and myosin filaments.

Figure Q9-27 shows the nucleotide sequence from a protein-coding region of a gene in humans, chimpanzees, and gorillas and the protein sequence produced from this gene. The seventeen amino acids encoded by this DNA are numbered below. The two codons that are not conserved in all three species have been boxed. These two codons code for amino acids 3 and 15. Figure Q9-27 (Amino acid 3= Human-AAA, Chimp- AAG, Gorilla-AAG; Amino acid 15= Human-CCC, Chimp-CCT, Gorilla-CCC) Which of these statements is consistent with these sequence-comparison data? (a) The gorilla sequence is more similar to the chimp sequence than to the human sequence. (b) Since these sequences are so similar, this protein must also be found in invertebrates. (c) The chimp DNA sequence has likely diverged at the DNA coding for amino acid 15 from the sequence found in the last common ancestor of humans and chimps. (d) The last common ancestor of chimps and gorillas most likely used AAA to code for amino acid number 3.

What is the cause of the massive amount of programmed cell death of nerve cells (neurons) that occurs in the developing vertebrate nervous system, and what purpose does it serve?

Immature neurons are produced in excess of the number that will eventually be required. They compete for the limited amount of survival factors secreted by the target cells they contact. Those cells that fail to get enough survival factor undergo programmed cell death. Up to half or more of the original nerve cells die in this way. This competitive mechanism helps match the number of developing nerve cells to the number of target cells they contact.

What is the main molecular difference between cells in a G0 state and cells that have simply paused in G1?

In G0, the cell-cycle control system is partly dismantled, so that some of the Cdks and cyclins are not present. Cells paused in G1, by contrast, still contain all the components of the cell-cycle control system. Whereas the latter cells can rapidly progress through the cycle when conditions are right, G0 cells need to synthesize the missing cell-cycle control proteins so as to re-enter the cycle, which usually takes 8 hours or more.

In humans and in chimpanzees, 99% of the Alu retrotransposons are in corresponding positions. Which of the following statements below is the most likely explanation for this similarity? (a) The Alu retrotransposon is not capable of transposition in humans. (b) Most of the Alu sequences in the chimpanzee genome underwent duplication and divergence before humans and chimpanzees diverged. (c) The Alu retrotransposons are in the most beneficial position in the genome for primates. (d) The Alu retrotransposons must also be in the same position in flies

No (these genes are likely to be involved in basic cellular functions such as DNA replication and protein production, and in the basic functions of eukaryotic cells such as the functioning of the nucleus and the movement of items between cellular compartments. Genes involved in basic cellular functions are likely to be used all the time in an organism's life and are not likely to be activated at a specific stage of life. The genes found in all eukaryotes probably existed in the primordial eukaryotic cells.)

It is thought that all eukaryotes have about 300 genes in common. Would you predict that these genes would be used at different times during the life cycle of multicellular animals?

Mobile genetic elements are sometimes called "jumping genes" because they move from place to place throughout the genome. The exact mechanism by which they achieve this mobility depends on the genes contained within the mobile element. Which of the following mobile genetic elements carries both a transposase and a reverse transcriptase gene?

Why should it be that drugs such as colchicine, which inhibit microtubule polymerization, and drugs such as Taxol®, which stabilize microtubules, both inhibit mitosis?

Mitosis requires that the spindle microtubules behave dynamically—continuously polymerizing and depolymerizing—to probe the cell cortex, to seek attachments to kinetochores, and to segregate the chromosomes. Static microtubules are unable to do any of these things.

Mobile genetic elements are sometimes called "jumping genes," because they move from place to place throughout the genome. The exact mechanism by which they achieve this mobility depends on the genes contained within the mobile element. Which of the following mobile genetic elements carries both a transposase gene and a reverse transcriptase gene? (a) L1 (b) B1 (c) Alu (d) Tn3

single-nucleotide polymorphisms, Exon shuffling, horizontal gene transfer, gene duplication, divergence

Most variation between individual humans is in the form of __________________. __________________ may arise by recombination within introns and can create proteins with novel combinations of domains. Scientists and government regulators must be very careful when introducing herbicideresistant transgenic corn plants into the environment, because if resistant weeds arise from __________________ then the herbicides could become useless. Families of related genes can arise from a single ancestral copy by __________________ and subsequent __________________. divergence purifying selection exon shuffling single-nucleotide polymorphisms gene duplication synteny horizontal gene transfer unequal crossing-over

The number of cells in an adult tissue or animal depends on cell proliferation. What else does it depend on?

Programmed cell death also influences cell numbers. Most animal cells require survival signals from other cells to avoid programmed cell death, so that the levels of such signals can help determine how many cells live and how many die.

Unequal genetic exchange in homologous recombination

Propose a reason to explain why highly repetitive regions of the genome are particularly susceptible to expansions and contractions in number

The number of distinct protein species found in humans and other organisms can vastly exceed the number of genes. This is largely due to ______________. (a) protein degradation. (b) alternative splicing. (c) homologous genes. (d) mutation.

gamete, zygote, somatic, neutral, deleterious

Sexual reproduction in a multicellular organism involves specialized reproductive cells, called __________________s, which come together to form a __________________ that will divide to produce both reproductive and __________________ cells. A point mutation in the DNA is considered a __________________ mutation if it changes a nucleotide that leads to no phenotypic consequence; a point mutation is considered __________________ if it changes a nucleotide within a gene and causes the protein to be nonfunctional. cellulose intron common neutral deleterious somatic gamete unequal homologous zygote

Can signaling via a steroid hormone receptor lead to amplification of the original signal? If so, how?

Since the interactions of the signal molecule with its receptor and of the activated receptor with the regulatory region of a target gene are both one-to-one, there is no amplification. The signal can be amplified with the target gene is transcribed, since multiple copies of mRNA are usually produced from a gene once it has been switched on, and multiple copies of protein can be made from each mRNA molecule.

Intracellular steroid hormone receptors have binding sites for a signaling molecule and a DNA sequence. How is it that the same steroid hormone receptor, which binds to a specific DNA sequence, can regulate different genes in different cell types?

Steroid hormone receptors, after binding to a specific DNA sequence, can set off primary and secondary response proteins, activating and deactivating different portions of DNA transcription, resulting in differing regulation in different cell types.

True

T/F: A pseudogene is very similar to a functional gene but cannot be expressed because of mutations.

False (Many highly conserved stretches of DNA are not transcribed but instead contain information critical for regulating where and when genes are expressed)

T/F: All highly conserved stretches of DNA in the genome are transcribed into RNA

False (By some estimates, 20% of the genomic DNA in some bacterial species arose by horizontal gene transfer.)

T/F: Horizontal gene transfer is very rare and thus has had little influence on the genomes of bacteria.

False (Introns and transposons can act as sites where recombinational crossovers occur. Transposons can also catalyze genetic rearrangements. Rearrangements occurring within these sequences are less likely to be detrimental than those occurring elsewhere in the genome. In general, only the short intron sequences required for splicing are important to intron function; alterations in sequences outside the splicing sites may have no consequences for intron function and thus will not be subject to purifying selection)

T/F: Introns and transposons tend to slow the evolution of new genes.

False (A large proportion of the genes in vertebrates (and many other species) are members of multigene families.)

T/F: Most genes in vertebrates are unique, and only a few genes are members of multigene families

True

T/F: Most mutations and genome alterations have neutral consequences

True

T/F: Most single-nucleotide polymorphisms cause no observable functional differences between individual humans

False (Many duplications are subsequently lost or become pseudogenes, and only a few evolve into new genes.)

T/F: Nearly every instance of DNA duplication leads to a new functional gene.

True

T/F: Proteins required for growth, metabolism, and cell division are more highly conserved than those involved in development and in response to the environment

True

T/F: Repeats of the CA dinucleotide are useful for crime investigations and other forensic applications

False (Multicellular organisms are built from essentially the same toolbox of gene building blocks, but the parts are put together differently because of regulatory differences that dictate when and where and how much of each protein is made. Alternative splicing can also have an important role, as it can generate several proteins from a single gene in some species, yet the homologous gene in other species may produce only one protein)

T/F: The differences between multicellular organisms are largely explained by the different kinds of genes carried on their chromosomes.

False ( The number of genes differs only by about a factor of two. It is thought that the increased complexity of humans is due largely to differences in when and where the genes are expressed. Differences in the timing of splicing may also be a major contributor to the relative complexity of humans.)

T/F: The increased complexity of humans compared with flies and worms is largely due to the vastly larger number of genes in humans.

False ( Human and mouse chromosomes show extensive synteny, with blocks of chromosomal DNA exhibiting homologous genes arranged in the same order between the two species.)

T/F: There is little conserved synteny between human and mouse genes

True

T/F: To find functionally important regions of the genome, it is more useful to compare species whose last common ancestor lived 100 million years ago rather than 5 million years ago

False (Evolution can work only by tinkering with the tools and materials on hand, not by starting from scratch to make completely new genes or pathways. New functions arise from the ancestral functions by a process of gradual mutational change, and thus may not represent the best possible solution to a problem)

T/F: To meet a challenge or develop a new function, evolution essentially builds from first principles, designing from scratch, to find the best possible solution.

Antibodies are Y-shaped molecules that have two identical binding sites. Suppose that you have obtained an antibody that is specific for the extracellular domain of an RTK. When the antibody binds to the RTK, it brings together two RTK molecules. If cells containing the RTK were exposed to the antibody, would you expect the kinase to be activated, inactivated, or unaffected? Explain your reasoning.

The RTK will probably become activated on binding of the antibody molecule. This is because signal-induced dimerization usually activates RTKs. When RTK molecules are brought together, their cytoplasmic kinase domains become activated and each receptor phosphorylates the other.

What would happen to the progeny of a cell that proceeded to mitosis and cell division after entering S phase but had not completed S phase? Keep in mind that highly condensed chromatin, including the centromere region, is replicated late in S phase. Explain your answer.

The daughter cells would probably die. Those chromosomes that had not completed replication in S phase would have only one centromere, because the centromere is the last part of the chromosome to be replicated; the chromosome would therefore be segregated to only one of the two daughter cells at random. At least one, and probably both, of the daughter cells would thus receive an incomplete set of chromosomes and would be unlikely to be viable. Even if one daughter cell, by chance, received a full set of chromosomes, some of these chromosomes would be incompletely replicated and the cell would probably still not be viable.

For each of the following sentences, fill in the blanks with the best word or phrase

The four phases of the cell cycle, in order, are G1, S, M, and G2. A cell contains the most DNA after S phase of the cell cycle. A cell is smallest in size after M phase of the cell cycle. Growth occurs in G1, S, and G2 phases of the cell cycle. A cell does not enter mitosis until it has completed DNA synthesis.

37 days (approx.)

The human genome has 3.2 × 10^9 nucleotide pairs. At its peak, the Human Genome Project was generating raw nucleotide sequences at a rate of 1000 nucleotides per second. At the rate of 1000 nucleotides per second, how long would it take to generate 3.2 × 10^9 nucleotides of sequence?

Some lower vertebrates such as fish and amphibians can control their color by regulating specialized pigment cells called melanophores. These cells contain small, pigmented organelles, termed melanosomes, that can be dispersed throughout the cell, making the cell darker, or aggregated in the center of the cell to make the cell lighter. You purify the melanosomes from melanophores that have either aggregated or dispersed melanosomes and find that: 1. aggregated melanosomes co-purify with dynein; 2. dispersed melanosomes co-purify with kinesin. Given this set of data, propose a mechanism for how the aggregation and dispersal of melanosomes occur.

The melanosomes are transported in the cell on microtubules. When it is advantageous for the animal cell to become lighter, a signal is sent to the pigment cell that causes the melanosomes to associate with dynein. Because dynein is a minus-end directed motor, it will transport the melanaosmes toward the center of the cell, causing the melanosomes to aggregate in the center and the cell to take on a lighter appearance. When the animal wants to become darker, a signal is sent to the pigment cell that causes the melanosomes to associate with kinesin. Kinesin is usually a plus-end directed motor and will move the melanosomes away from the center of the cell so that they are more dispersed, making the cell look darker.

Your friend is studying mouse fur color and has isolated the GPCR responsible for determining its color, as well as the extracellular signal that activates the receptor. She finds that, on addition of the signal to pigment cells (cells that produce the pigment determining fur color), cAMP levels rise in the cell. She starts a biotech company, and the company isolates more components of the signaling pathway responsible for fur color. Using transgenic mouse technology, the company genetically engineers mice that are defective in various proteins involved in determining fur color. The company obtains the following results. Normal mice have beige (very light brown) fur color. Mice lacking the extracellular signal have white fur. Mice lacking the GPCR have white fur. Mice lacking cAMP phosphodiesterase have dark brown fur. Your friend has also made mice that are defective in the α subunit of the G protein in this signaling pathway. The defective α subunit works normally except that, once it binds GTP, it cannot hydrolyze GTP to GDP. What color do you predict that the fur of these mice will be? Why?

The mice with defective alpha subunit should have white fur. We can see that any block in signal due to absence of extracellular signal or defective GPCR lead to mice with white fur. Thus, with defective G-protein the signal will be blocked. If the signal is not regulated, the synthesis of the some pigment protein becomes constituitive and that results in dark brown fur.

In what state would the muscle be if you added Ca2+ but no ATP?

The muscle will be in a rigor state if Ca2+ is added without ATP. Troponin can bind to Ca2+ undergoing a conform change, so tropomyosin shifts and exposes actin for myosin to bind. However, myosin will bind actin and remain in the attached because a myosin head lacking a bound nucleotide is locked onto the actin until nucleotide binding occurs.

Activated GPCRs activate G proteins by reducing the strength of binding of GDP to the α subunit of the G protein, allowing GDP to dissociate and GTP (which is present at much higher concentrations in the cell than GDP) to bind in its place. How would the activity of a G protein be affected by a mutation that reduces the affinity of the α subunit for GDP without significantly changing its affinity for GTP?

The mutant G protein would be constantly active. Each time the subunit hydrolyzed GTP to GDP, the GDP would dissociate, allowing GTP to bind and reactivate the subunit. Normally, GDP is tightly bound by the subunit. Normally, GDP is tightly bound by the subunit, keeping the G protein in its inactive state until release of GDP is stimulated by interactions with an appropriate activated G-protein-linked receptor.

T/F: Stage 2 of photosynthesis involves a cycle of reactions that does not directly depend on energy derived from sunlight

True

The pufferfish, Fugu rubripes, has a genome that is one-tenth the size of mammalian genomes. Which of the following statements is not a possible reason for this size difference? (a) Intron sequences in Fugu are shorter than those in mammals. (b) Fugu lacks the repetitive DNA found in mammals. (c) The Fugu genome seems to have lost sequences faster than it has gained sequences over evolutionary time. (d) Fugu has lost many genes that are part of gene families.

You have isolated a mutant in which a fraction of the new cells die soon after cell division and a fraction of the living cells have an extra copy of one or more chromosomes. When you grow the cells under conditions in which they transit the cell cycle more slowly, the defect disappears, suggesting that the mitotic spindle and segregation machinery are normal. Propose a basis for the defect.

This mutant may be lacking the checkpoint mechanism that delays the onset of anaphase and chromosome segregation until all chromosomes have attached properly to the mitotic spindle. If cells attempt chromosome segregation before all chromosomes have attached properly, some of the daughter cells will receive too few chromosomes (and thus will probably die) and other cells will receive additional chromosomes. Normally, cells use such a surveillance system to monitor the spindle attachment of each chromosome and engage molecular brakes until all chromosomes have attached properly. The molecular brakes will be dispensable in some dividing cells if all of the chromosomes rapidly become properly attached to the spindle. In other dividing cells, it will take longer for some of the chromosomes to find their appropriate attachments, and thus the molecular brakes will be essential to ensure faithful segregation of the duplicated copies of each chromosome to the two daughter cells. Slowing the cycle will allow more cells to segregate their chromosomes properly even in the absence of this "spindle attachment" checkpoint.

Only if it was in a gamete cell

Transposable elements litter the genomes of primates, and a few of them are still capable of moving to new regions of the genome. If a transposable element jumped into an important gene in one of your cells when you were a baby and caused a disease, is it likely that your child would also have the disease? Explain.

Before chromosomes segregate in M phase, they and the segregation machinery must be appropriately prepared. Indicate whether the following statements are true or false Each centrosome contains a pair of centrioles and hundreds of γ-tubulin rings that nucleate the growth of microtubules.

True

Before chromosomes segregate in M phase, they and the segregation machinery must be appropriately prepared. Indicate whether the following statements are true or false Microtubule-dependent motor proteins and microtubule polymerization and depolymerization are mainly responsible for the organized movements of chromosomes during mitosis.

True

Is the following statement true or false? After the nuclear envelope breaks down, microtubules gain access to the chromosomes and, every so often, a randomly probing microtubule captures a chromosome and ultimately connects to the kinetochore to become a kinetochore microtubule of the spindle.

True

T or F? Most mutation and genome alterations have neutral consequences

True

T or F? Proteins required for growth, metabolism, and cell division are more highly conserved than those involved in development and in response to the environment.

True

T/F: ATP is moved out of the matrix, across the inner mitochondrial membrane, in a co-transporter that also brings ADP into the matrix.

True

T/F: Amino acids can be transported into the mitochondria and converted into acetyl CoA.

True

T/F: Anaerobic respiration is not the same as fermentation, as only the former requires an electron-transport chain.

True

T/F: CO2 and H2O are generated during the oxidation of food molecules.

True

T/F: CO2 and O2 are water-soluble molecules that diffuse freely across cell membranes

True

T/F: Carbon fixation can be described as a process by which gaseous carboncontaining molecules are captured and incorporated into biological hydrocarbon molecules.

True

T/F: Cells expend energy in the form of ATP hydrolysis so as to maintain ion concentrations that differ from those found outside the cell.

True

T/F: Cytochrome c oxidase binds O2 using an iron-heme group, where four electrons are shuttled one at a time.

True

T/F: Most ion channels are gated, which allows them to open and close in response to a specific stimulus, rather than allowing the constant, unregulated flow of ions

True

T/F: Much of the glyceraldehyde 3-phosphate made in the chloroplast ends up producing the molecules needed by the mitochondria to produce ATP.

True

T/F: Neurotransmitters are small molecules released into the synaptic cleft after the fusion of synaptic vesicles with the presynaptic membrane

True

T/F: Ribulose 1,5-bisphosphate is similar to oxaloacetate in the Krebs cycle in that they are both regenerated at the end of their respective cycles.

True

TorF? To find functionally important regions of the genome, it is more useful to compare species whose last common ancestor lived 100 million years go rather than 5 million years ago

True

True or false - Proto-oncogenes play an important role in controlling the division of normal cells.

True

True or false - Using just 3 genes, scientists can transform adult cells into cells that behave like embryonic stem cells.

True

True or false - cells joined together in epithelial sheets line all external and internal surfaces of the animal body.

True

True or false - most cases of cervical cancer are caused by a viral infection.

True

Are the statements below true or false? Explain your answer. Statement 1: Generally, in a given organism, the S, G2, and M phases of the cell cycle take a defined and stereotyped amount of time in most cells.

True. In nearly all cells in an organism, the S, G2, and M phases of the cell cycle take the same amount of time. The different timing of cell division in different cell types is due to variable lengths of the G1 phase or to withdrawal into the G0 state.

Viral genomes _________. (a) can be made of DNA. (b) can be made of RNA. (c) can be either double-stranded or single-stranded. (d) All answers above are true.

What is the most likely explanation of why the overall mutation rates in bacteria and in humans are roughly similar? (a) Cell division needs to be fast. (b) Most mutations are silent. (c) There is a narrow range of mutation rates that offers an optimal balance between keeping the genome stable and generating sufficient diversity in a population. (d) It benefits a multicellular organism to have some variability among its cells.

neutral, detrimental, beneficial

When a mutation arises, it can have three possible consequences: beneficial to the individual, selectively neutral, or detrimental. Order these from most likely to least likely

Which of the following DNA sequences is not commonly carried on a DNA-only transposon? (a) transposase gene (b) reverse transcriptase gene (c) recognition site for transposase (d) antibiotic-resistance gene

Which of the following functions do you not expect to find in the set of genes found in all organisms on Earth? (a) DNA replication (b) DNA repair (c) protein production (d) RNA splicing

Which of the following is true of a retrovirus but not of the Alu retrotransposon? (a) It requires cellular enzymes to make copies. (b) It can be inserted into the genome. (c) It can be excised and moved to a new location in the genome. (d) It encodes its own reverse transcriptase.

Which of the following processes is not thought to contribute to diversity in the genome of human individuals? (a) exon shuffling (b) single-nucleotide polymorphisms (c) CA repeats (d) duplication and deletion of large blocks of sequence

Which of the following regions of the genome is the least likely to be conserved over evolutionary time? (a) the upstream regulatory region of a gene that encodes the region conferring tissue specificity (b) the upstream regulatory region of a gene that binds to RNA polymerase (c) the portion of the genome that codes for proteins (d) the portion of the genome that codes for RNAs that are not translated into protein

Which of the following statements about gene families is false? (a) Because gene duplication can occur when crossover events occur, genes are always duplicated onto homologous chromosomes. (b) Not all duplicated genes will become functional members of gene families. (c) Whole-genome duplication can contribute to the formation of gene families. (d) Duplicated genes can diverge in both their regulatory regions and their coding regions.

Which of the following statements about homologous genes is true? (a) For protein-coding genes, homologous genes will show more similarity in their amino acid sequences than in their nucleotide sequences. (b) Fewer than 1% of human genes have homologs in the nematode and the fruit fly. (c) Most homologous genes arose by gene duplication. (d) A gene in humans that has homologs in plants and prokaryotes will show the same level of similarity in nucleotide sequence when the human and prokaryotic sequences are compared as when the human and chimpanzee sequences are compared

Which of the following statements about mobile genetic elements is true? (a) Mobile genetic elements can sometimes rearrange the DNA sequences of the genome in which they are embedded by accidentally excising neighboring chromosomal regions and reinserting these sequences into different places within the genome. (b) DNA-only transposons do not code for proteins but instead rely on transposases found in cells that are infected by viruses. (c) The two major families of transposable sequences found in the human genome are DNA-only transposons that move by replicative transposition. (d) During cut-and-paste transposition, the donor DNA will no longer have the mobile genetic element embedded in its sequence when transposition is complete

Which of the following statements about pseudogenes is false? (a) Pseudogenes code for microRNAs. (b) Pseudogenes share significant nucleotide similarity with functional genes. (c) Pseudogenes are no longer expressed in the cell. (d) There are estimated to be approximately 20,000 pseudogenes in the human genome.

Which of the following statements about the globin gene family is true? (a) The globin protein, which can carry oxygen molecules throughout an organism's body, was first seen in ancient vertebrate species about 500 million years ago. (b) The gene duplication that led to the expansion of the globin gene family led to the separation and distribution of globin on many chromosomes in mammals, such that no chromosome has more than a single functional member of the globin gene family. (c) As globin gene family members diverged over the course of evolution, all the DNA sequence variations that have accumulated between family members are within the regulatory DNA sequences that affect when and how strongly each globin gene is expressed. (d) Some of the duplicated globin genes that arose during vertebrate evolution acquired inactivating mutations and became pseudogenes in modern vertebrates.

Which of the following statements about the human genome is false? (a) About 50% of the human genome is made up of mobile genetic elements. (b) More of the human genome comprises intron sequences than exon sequences. (c) About 1.5% of the human genome codes for exons. (d) Only the exons are conserved between the genomes of humans and other mammals

Which of the following statements about what we have learned by comparing the modern-day human genome to other genomes is true? (a) Modern humans whose ancestors come from Europe or Asia share up to 4 percent of their genome with Neanderthals. (b) Accelerated changes, which were found when comparing the human genome to other mammalian genomes, were not found when comparing the modern-day human genome to the Neanderthal genome. (c) The human genome is far more gene-dense than the yeast genome. (d) In syntenic regions of the human and mouse genomes, both gene order and the placements of more than 95% of the mobile genetic elements are conserved.

Which of the following statements is false? (a) A mutation that arises in a mother's somatic cell often causes a disease in her daughter. (b) All mutations in an asexually reproducing single-celled organism are passed on to progeny. (c) In an evolutionary sense, somatic cells exist only to help propagate germline cells. (d) A mutation is passed on to offspring only if it is present in the germ line.

You are studying a gene that has four exons and can undergo alternative splicing. Exon 1 has two alternatives, exon 2 has five alternatives, exon 3 has three alternatives, and exon 4 has four alternatives. If all possible splicing combinations were used, how many different splice isoforms could be produced for this gene? (a) 22 (b) 30 (c) 60 (d) 120

You discover that the underlying cause of a disease is a protein that is now less stable than the non-disease-causing version of the protein. This change is most likely to be due to ________. (a) a mutation within a gene. (b) a mutation within the regulatory DNA of a gene. (c) gene duplication. (d) horizontal gene transfer.

You isolate a pathogenic strain of E. coli from a patient and discover that this E. coli strain is resistant to an antibiotic. Common laboratory strains of E. coli are not resistant to this antibiotic, nor are any other previously isolated pathogenic E. coli strains. However, such resistance has been observed in other bacteria in the hospital in which the patient was treated. This newly discovered antibiotic resistance in E. coli is most likely due to _______. (a) a mutation within a gene. (b) a mutation within the regulatory DNA of a gene. (c) gene duplication. (d) horizontal gene transfer.

A covalent bond between two atoms is formed as a result of the ______________. (a) sharing of electrons. (b) loss of electrons from both atoms. (c) loss of a proton from one atom. (d) transfer of electrons from one atom to the other.

Although covalent bonds are 10-100 times stronger than noncovalent interactions, many biological processes depend upon the number and type of noncovalent interactions between molecules. Which of the noncovalent interactions below will contribute most to the strong and speciﬁc binding of two molecules, such as a pair of proteins? (a) electrostatic attractions (b) hydrogen bonds (c) hydrophobic interactions (d) Van der Waals attractions

Aromatic carbon compounds such as benzene are planar and very stable. Double-bond character extends around the entire ring, which is why it is often drawn as a hexagon with a circle inside. This characteristic is caused by electron __________. (a) resonance. (b) pairing. (c) partial charge. (d) stacking

By definition, prokaryotic cells do not possess __________. (a) a nucleus. (b) replication machinery. (c) ribosomes. (d) membrane bilayers.

Cells use membranes to help maintain set ranges of ion concentrations inside and outside the cell. Which of the following ions is the most abundant outside a typical mammalian cell? (a) Na+ (b) K+ (c) Ca2+ (d) Cl-

Cyclic AMP (cAMP) is a small molecule that associates with its binding site with a high degree of speciﬁcity. Which types of noncovalent interactions are the most important for providing the "hand in a glove" binding of cAMP? (a) hydrogen bonds (b) electrostatic interactions (c) van der Waals interactions (d) hydrophobic interactions

Drosophila melanogaster is a/an __________. This type of animal is the most abundant of all animal species, making it an appropriate choice as an experimental model. (a) insect (b) bird (c) amphibian (d) mammal

During respiration, energy is retrieved from the high-energy bonds found in certain organic molecules. Which of the following, in addition to energy, are the ultimate products of respiration? (a) CO2, H2O (b) CH3, H2O (c) CH2OH, O2 (d) CO2, O2

Each nucleotide in DNA and RNA has an aromatic base. What is the principal force that keeps the bases in a polymer from interacting with water? (a) hydrophobic interactions (b) hydrogen bonds (c) covalent bonds (d) van der Waals interactions

Electron-transfer reactions occur rapidly. Which of the following statements best describes how the diffusion of ubiquinone is controlled in order to ensure its proximity to the other enzyme complexes? (a) Ubiquinone is anchored directly in the inner mitochondrial membrane via its hydrocarbon tail, and can only diffuse laterally. (b) Ubiquinone is present at high concentrations, minimizing the impact of diffusion on the electron-transport chain. (c) Ubiquinone becomes covalently attached to the other enzyme complexes. (d) The intermembrane space in the mitochondrion is relatively small, and therefore the random diffusion of these molecules is not a problem.

Eukaryotic cells are able to trigger the release of material from secretory vesicles to the extracellular space using a process called exocytosis. An example of materials commonly released this way is _____________. (a) hormones. (b) nucleic acids. (c) sugars. (d) cytosolic proteins.

Fermentation is a/an _____________________ process that converts _____________ into carbon dioxide and _____________________. (a) anaerobic, pyruvate, ethanol (b) anaerobic, lactate, ethanol (c) eukaryotic, glyceraldehyde 3-phosphate, ethanol (d) prokaryotic, lactate, propanol

Figure Q12-56 illustrates changes in membrane potential during the formation of an action potential. What membrane characteristic or measurement used to study action potentials is indicated by the arrow (between 1st and second line)? (a) effect of a depolarizing stimulus (b) resting membrane potential (c) threshold potential (d) action potential

Foods are broken down into simple molecular subunits for distribution and use throughout the body. Which type of simple subunits, listed below, is used preferentially as an energy source? (a) simple sugars (b) proteins (c) free fatty acids (d) glycerol

For some proteins, small molecules are integral to their structure and function. Enzymes can synthesize some of these small molecules, whereas others, called vitamins, must be ingested in the food we eat. Which of the following molecules is not classiﬁed as a vitamin but does require the ingestion of a vitamin for its production? (a) retinal (b) biotin (c) zinc (d) heme

For the reaction Y◊X at standard conditions with [Y] = 1 M and [X] = 1 M, ΔG is initially a large negative number. As the reaction proceeds, [Y] decreases and [X] increases until the system reaches equilibrium. How do the values of ΔG and ΔG° change as the reaction equilibrates? (a) ΔG becomes less negative and ΔG° stays the same. (b) ΔG becomes positive and ΔG° becomes positive. (c) ΔG stays the same and ΔG° becomes less negative. (d) ΔG reaches zero and ΔG° becomes more negative.

Globular proteins fold up into compact, spherical structures that have uneven surfaces. They tend to form multisubunit complexes, which also have a rounded shape. Fibrous proteins, in contrast, span relatively large distances within the cell and in the extracellular space. Which of the proteins below is not classiﬁed as a ﬁbrous protein? (a) elastase (b) collagen (c) keratin (d) elastin

Glycolysis is an anaerobic process used to catabolize glucose. What does it mean for this process to be anaerobic? (a) no oxygen is required (b) no oxidation occurs (c) it takes place in the lysosome (d) glucose is broken down by the addition of electrons

In stage 1 of photosynthesis, a proton gradient is generated and ATP is synthesized. Where do protons become concentrated in the chloroplast? (a) thylakoid space (b) stroma (c) inner membrane (d) thylakoid membrane

In step 4 of glycolysis, a six-carbon sugar (fructose 1,6-bisphosphate) is cleaved to produce two three-carbon molecules (dihydroxyacetone phosphate and glyceraldehyde 3-phosphate). Which enzyme catalyzes this reaction? (a) aldolase (b) phosphoglucose isomerase (c) enolase (d) triose phosphate isomerase

In step 4 of the citric acid cycle, the reduction of NAD+ to NADH is coupled to the generation of CO2 and the formation of a high-energy thioester bond. The energy of the thioester bond is harnessed in step 5. What is the energy used for? (a) to generate a molecule of GTP (b) to generate a molecule of ATP (c) to generate a proton gradient (d) to generate a molecule of NADH

In the final stage of the oxidation of food molecules, a gradient of protons is formed across the inner mitochondrial membrane, which is normally impermeable to protons. If cells were exposed to an agent that causes the membrane to become freely permeable to protons, which of the following effects would you expect to observe? (a) The ratio of ATP to ADP in the cytoplasm would fall. (b) NADH would build up. (c) Carbon dioxide production would cease. (d) The consumption of oxygen would fall

Instead of studying one or two proteins or protein complexes present in the cell at any given time, we can now look at a snapshot of all proteins being expressed in cells being grown in speciﬁc conditions. This large-scale, systematic approach to the study of proteins is called _______________. (a) proteomics. (b) structural biology. (c) systems biology. (d) genomics

Isomerization of glucose 1-phosphate to glucose 6-phosphate is energetically favorable. At 37°C, ΔG° = -1.42 log10K. What is the equilibrium constant for this reaction if ΔG° = -1.74 kcal/mole at 37°C? (a) 16.98 (b) 0.09 (c) -0.09 (d) 0.39

Many of the mechanisms that cells use for maintenance and reproduction were first studied at the molecular level in bacteria. Which bacterial species had a central role in advancing the field of molecular biology? (a) E. coli (b) D. melanogaster (c) S. pombe (d) C. elegans

Modern eukaryotes depend on mitochondria to generate most of the cell's ATP. How many molecules of ATP can a single molecule of glucose generate? (a) 30 (b) 2 (c) 20 (d) 36

Oxidation is a favorable process in an aerobic environment, which is the reason cells are able to derive energy from the oxidation of macromolecules. Once carbon has been oxidized to _______________, its most stable form, it can only cycle back into the organic portion of the carbon cycle through __________________. (a) CO2, photosynthesis. (b) CH3, combustion. (c) CO2, respiration. (d) CO, reduction.

Polypeptides are synthesized from amino acid building blocks. The condensation reaction between the growing polypeptide chain and the next amino acid to be added involves the loss of ________________. (a) a water molecule. (b) an amino group. (c) a carbon atom. (d) a carboxylic acid group.

Protein folding can be studied using a solution of puriﬁed protein and a denaturant (urea), a solvent that interferes with noncovalent interactions. Which of the following is observed after the denaturant is removed from the protein solution? (a) The polypeptide returns to its original conformation. (b) The polypeptide remains denatured. (c) The polypeptide forms solid aggregates and precipitates out of solution. (d) The polypeptide adopts a new, stable conformation.

Proteins can assemble to form large complexes that work coordinately, like moving parts inside a single machine. Which of the following steps in modulating the activity of a complex protein machine is least likely to be directly affected by ATP or GTP hydrolysis? (a) translation of protein components (b) conformational change of protein components (c) complex assembly (d) complex disassembly

Pumps are transporters that are able to harness energy provided by other components in the cells to drive the movement of solutes across membranes, against their concentration gradient. This type of transport is called _____________. (a) active transport. (b) free diffusion. (c) facilitated diffusion. (d) passive transport.

Select the option that best finishes the following statement: "Evolution is a process __________." (a) that can be understood based on the principles of mutation and selection. (b) that results from repeated cycles of adaptation over billions of years. (c) by which all present-day cells arose from 4-5 different ancestral cells. (d) that requires hundreds of thousands of years.

Several different classes of enzymes are needed for the catabolism of carbohydrates. Which of the following descriptions best matches the function of an isomerase? (a) An enzyme that catalyzes the rearrangement of bonds within a single molecule. (b) An enzyme that catalyzes a change in the position of a specific chemical group within a single molecule. (c) An enzyme that catalyzes the oxidation of a molecule by removing a hydride ion. (d) An enzyme that catalyzes the addition of phosphate groups to other molecules.

The citric acid cycle is a critical sequence of reactions for energy production, which take place in the matrix of the mitochondria. The reaction cycle requires materials from the cytosol to be converted into acetyl CoA, which represents the starting point of a new cycle. Which of the following statements about acetyl CoA is true? (a) Amino acids can be converted into acetyl CoA. (b) Pyruvate is converted into acetyl CoA in the cytosol. (c) Triacylglycerol molecules are transported into the mitochondrial matrix and cleaved by lipases to produce acetyl CoA. (d) Oxaloacetate is converted directly into acetyl CoA to feed the citric acid cycle.

The citric acid cycle is a series of oxidation reactions that removes carbon atoms from substrates in the form of CO2. Where do the oxygen atoms in the carbon dioxide molecules come from? (a) water (b) phosphates (c) molecular oxygen (d) acetyl CoA

The conversion of glyceraldehyde 3-phosphate to 1,3 bisphosphoglycerate in step 6 of glycolysis generates a "high energy" phosphoanhydride bond. Which of the following best describes what happens to that bond in step 7? (a) It is hydrolyzed to drive the formation of ATP. (b) It is hydrolyzed to drive the formation of NADH. (c) It is hydrolyzed to generate pyruvate. (d) It is oxidized to CO2.

Which of the following cells rely exclusively on glycolysis to supply them with ATP? (a) anaerobically growing yeast (b) aerobic bacteria (c) skeletal muscle cells (d) plant cells

The flow of genetic information is controlled by a series of biochemical reactions that result in the production of proteins, each with its own specific order of amino acids. Choose the correct series of biochemical reactions from the options presented here. (a) replication, transcription, translation (b) replication, translation, transcription (c) translation, transcription, replication (d) translation, replication, transcription

The link between bond-forming reactions and membrane transport processes in the mitochondria is called __________________. (a) chemiosmotic coupling. (b) proton pumping. (c) electron transfer. (d) ATP synthesis.

The mitochondrial proteins found in the inner membrane are involved in the conversion of ADP to ATP, a source of energy for the cell. This process consumes which of the following substances? (a) oxygen (b) nitrogen (c) sulfur (d) carbon dioxide

The net distance a molecule travels through the cytosol via diffusion is relatively short in comparison with the total distance it may need to travel. This is because movement governed by diffusion alone is a ________________ process that is most effective for the dispersion of small molecules over short distances. (a) slow (b) random (c) regulated (d) complicated

The oxygen-dependent reactions required for cellular respiration were originally thought to occur in a linear pathway. By using a competitive inhibitor for one enzyme in the pathway, investigators discovered that these reactions occur in a cycle. What compound served as the inhibitor? (a) malonate (b) malate (c) fumarate (d) succinate

The principal microtubule-organizing center in animal cells is the ____________. (a) centrosome. (b) centromere. (c) kinetochore. (d) cell cortex.

The process of generating monoclonal antibodies is labor-intensive and expensive. An alternative is to use polyclonal antibodies. A subpopulation of puriﬁed polyclonal antibodies that recognize a particular antigen can be isolated by chromatography. Which type of chromatography is used for this purpose? (a) afﬁnity (b) ion-exchange (c) gel-ﬁltration (d) any of the above

The relationship of free-energy change (ΔG) to the concentrations of reactants and products is important because it predicts the direction of spontaneous chemical reactions. In the hydrolysis of ATP to ADP and inorganic phosphate (Pi), the standard free-energy change (ΔG°) is -7.3 kcal/mole. The free-energy change depends on concentrations according to the following equation: ΔG = ΔG° + 1.42 log10 ([ADP] [Pi]/[ATP]) In a resting muscle, the concentrations of ATP, ADP, and Pi are approximately 0.005 M, 0.001 M, and 0.010 M, respectively. What is the ΔG for ATP hydrolysis in resting muscle? (a) -11.1 kcal/mole (b) -8.72 kcal/mole (c) 6.01 kcal/mole (d) -5.88 kcal/mole

The stimulation of a motor neuron ultimately results in the release of a neurotransmitter at the synapse between the neuron and a muscle cell. What type of neurotransmitter is used at these neuromuscular junctions? (a) acetylcholine (b) glutamate (c) GABA (d) glycine

The study of enzymes also includes an examination of how the activity is regulated. Molecules that can act as competitive inhibitors for a speciﬁc reaction are often similar in shape and size to the enzyme's substrate. Which variable(s) used to describe enzyme activity will remain the same in the presence and absence of a competitive inhibitor? (a) Vmax (b) V (c) Vmax and Km (d) Km

The three-dimensional coordinates of atoms within a folded protein are determined experimentally. After researchers obtain a protein's structural details, they can use different techniques to highlight particular aspects of the structure. What visual model best displays a protein's secondary structures (α helices and β sheets)? (a) ribbon (b) space-ﬁlling (c) backbone (d) wire

There are 20^100 different possible sequence combinations for a protein chain with 100 amino acids. In addition to the amino acid sequence of the protein, what other factors increase the potential for diversity in these macromolecules? (a) free rotation around single bonds during synthesis (b) noncovalent interactions sampled as protein folds (c) the directionality of amino acids being added (d) the planar nature of the peptide bond

Transporters, in contrast to channels, work by ________________. (a) specific binding to solutes. (b) a gating mechanism. (c) filtering solutes by charge. (d) filtering solutes by size

Voltage-gated channels contain charged protein domains, which are sensitive to changes in membrane potential. By responding to a threshold in the membrane potential, these voltage sensors trigger the opening of the channels. Which of the following best describes the behavior of a population of channels exposed to such a threshold? (a) Some channels remain closed and some open completely. (b) All channels open completely. (c) All channels open partly, to the same degree. (d) All channels open partly, each to a different degree

We can test the relative permeability of a phospholipid bilayer by using a synthetic membrane that does not contain any protein components. Some uncharged, polar molecules are found to diffuse freely across these membranes, to varying degrees. Which of the following has the lowest rate of diffusion across an artificial membrane? (a) glucose (b) water (c) glycerol (d) ethanol

What information regarding an enzyme-catalyzed reaction is obtained in a plot of the inverse of the initial velocities against the inverse of the corresponding substrate concentrations? (a) 1/Vmax and 1/Km (b) 1/V and 1/[S] (c) Vmax and Km (d) V and [S]

What purpose does the phosphorylation of glucose to glucose 6-phosphate by the enzyme hexokinase serve as the first step in glycolysis? (a) It helps drive the uptake of glucose from outside the cell. (b) It generates a high-energy phosphate bond. (c) It converts ATP to a more useful form. (d) It enables the glucose 6-phosphate to be recognized by phosphofructokinase, the next enzyme in the glycolytic pathway

When glucose is being used up and not replaced from food intake, the blood sugar level can be maintained by synthesizing glucose from smaller molecules such as pyruvate or lactate. This process is called gluconeogenesis. Which organ is principally responsible for supplying glucose to the rest of the body when glucose reserves are low? (a) liver (b) pancreas (c) spleen (d) gall bladder

Which of the following channels would not be expected to generate a change in voltage by movement of its substrate across the membrane where it is found? (a) an aquaporin (b) a sodium channel (c) a calcium channel (d) a proton channel

Which of the following elements is least abundant in living organisms? (a) sulfur (b) carbon (c) oxygen (d) nitrogen

Which of the following expressions accurately describes the calculation of pH? (a) pH = -log10[H+]+ (b) pH = log10[H] (c) pH = -log2[H+] (d) pH = -log10[OH-]

Which of the following factors do not inﬂuence the length of a covalent bond? (a) the tendency of atoms to ﬁll the outer electron shells (b) the attractive forces between negatively charged electrons and positively charged nuclei (c) the repulsive forces between the positively charged nuclei (d) the minimization of repulsive forces between the two nuclei by the cloud of shared electrons

Which of the following globular proteins is used to form ﬁlaments as an intermediate step to assembly into hollow tubes? (a) tubulin (b) actin (c) keratin (d) collagen

Which of the following is not a feature commonly observed in α helices? (a) left-handedness (b) one helical turn every 3.6 amino acids (c) cylindrical shape (d) amino acid side chains that point outward

Which of the following methods would be the most suitable to assess whether your protein exists as a monomer or in a complex? (a) gel-ﬁltration chromatography (b) gel electrophoresis (c) western blot analysis (d) ion-exchange chromatography

Which of the following statements about allostery is true? (a) of in the same Allosteric regulators are often products other chemical reactions biochemical pathway. (b) Allosteric regulation is always used for negative regulation of enzyme activity. (c) Enzymes are the only types of proteins that are subject to allosteric regulation. (d) Binding of allosteric molecules usually locks an enzyme in its current conformation, such that the enzyme cannot adopt a different conformation.

Which of the following statements describes the mitochondrial outer membrane? (a) It is permeable to molecules with molecular mass as high as 5000 daltons. (b) It contains transporters for ATP molecules. (c) It contains proteins that are released during apoptosis. (d) It contains enzymes required for the oxidation of fatty acids.

Which of the following statements describes the phosphorylation event that occurs during the process known as oxidative phosphorylation? (a) A phosphate group is added to ADP. (b) ATP is hydrolyzed in order to add phosphate groups to protein substrates. (c) A phosphate group is added to molecular oxygen. (d) Inorganic phosphate is transported into the mitochondrial matrix, increasing the local phosphate concentration.

Which ratio of NADH to NAD+ in solution will generate the largest positive redox potential? (a) 1:10 (b) 10:1 (c) 1:1 (d) 5:1

Which subatomic particles contribute to the atomic number for any given element? (a) protons (b) protons and neutrons (c) neutrons (d) protons and electrons

You have two puriﬁed samples of protein Y: the wild-type (nonmutated) protein and a mutant version with a single amino acid substitution. When washed through the same gel- ﬁltration column, mutant protein Y runs through the column more slowly than the normal protein. Which of the following changes in the mutant protein is most likely to explain this result? (a) the loss of a binding site on the mutant-protein surface through which protein Y normally forms dimers (b) a change that results in the mutant protein acquiring an overall positive instead of a negative charge (c) a change that results in the mutant protein being larger than the wild-type protein (d) a change that results in the mutant protein having a slightly different shape from the wild-type protein

In the ﬁrst stage of photosynthesis, light energy is converted into what other form of energy? (a) electrical (b) chemical (c) potential (d) kinetic

a or d

Match the following labels to the numbered lines on Figure Q17-27. A. minus end of microtubule B. tail of motor protein C. cargo of motor protein D. head of motor protein Which of the two motors in Figure Q17-27 is most probably a kinesin? Explain your answer.

a) 4 b) 2 c) 1 d) 3 The top one is most probably a kinesin because most kinesins walk towards the positive end of a microtubule.

Microtubules are formed from the tubulin heterodimer, which is composed of the nucleotide-binding ____a______________ protein and the _____b_____________ protein. Tubulin dimers are stacked together into protofilaments; _________c_________ parallel protofilaments form the tubelike structure of a microtubule. _______d___________ rings are important for microtubule nucleation and are found in the ________e__________ , which is usually found near the cell's nucleus in cells that are not undergoing mitosis. A microtubule that is quickly growing will have a ________f__________ cap that helps prevent the loss of subunits from its growing end. Stable microtubules are used in cilia and flagella; these microtubules are nucleated from a _______g___________ and involve a "______h____________ plus two" array of microtubules. The motor protein _________i_________ generates the bending motion in cilia; the lack of this protein can cause Kartagener's syndrome in humans.

a) a-tubulin b) B-tubulin c) thirteen d) y-tubulin e) centrosome f) GTP g) basal body h) nine i) dynein

Which of the situations below will enhance microtubule shrinkage? (a) addition of a drug that inhibits GTP exchange on free tubulin dimers (b) addition of a drug that inhibits GTP hydrolysis of tubulin dimers (c) addition of a drug that increases the affinity of tubulin molecules carrying GDP for other tubulin molecules (d) addition of a drug that blocks the ability of a tubulin dimer to bind to γ-tubulin

a) addition of a drug that inhibits GTP exchange on free tubular dimers

Acetylcholine binds to a GPCR on heart muscle, making the heart beat more slowly. The activated receptor stimulates a G protein, which opens a K+ channel in the plasma membrane, as shown in Figure Q16-25. Which of the following would enhance this effect of the acetylcholine? (a) addition of a high concentration of a non-hydrolyzable analog of GTP (b) addition of a drug that prevents the α subunit from exchanging GDP for GTP (c) mutations in the acetylcholine receptor that weaken the interaction between the receptor and acetylcholine (d) mutations in the acetylcholine receptor that weaken the interaction between the receptor and the G protein

a) addition of a high concentration of a non-hydrolyzable analog of GTP

Circle the phrase in each pair that is likely to occur more rapidly in response to an extracellular signal. A. changes in cell secretion / increased cell division B. changes in protein phosphorylation / changes in proteins being synthesized C. changes in mRNA levels / changes in membrane potential

a) changes in cell secretion b) changes in protein phosphorylation c) changes in membrane potential

Indicate whether each of the following statements refers to a ciliary microtubule, a microtubule of the mitotic spindle, both types of microtubule, or neither type of microtubule. A. The basal body is the organizing center. B. The monomer is sequestered by profilin. C. It is arranged in a "9 + 2" array. D. It is nucleated at the centrosome. E. It uses dynein motors. F. It is involved in sperm motility. G. It is involved in moving fluid over the surface of cells.

a) ciliary b) neither c) ciliary d) mitotic spindle e) both f) flagella d) cilliary

Which of the following mechanisms is not directly involved in inactivating an activated RTK? (a) dephosphorylation by serine/threonine phosphatases (b) dephosphorylation by protein tyrosine phosphatases (c) removal of the RTK from the plasma membrane by endocytosis (d) digestion of the RTK in lysosomes

a) dephosphorylation by serin/.threonine phosphataes

Which of the following statements is true? (a) Extracellular signal molecules that are hydrophilic must bind to a cell- surface receptor so as to signal a target cell to change its behavior. (b) To function, all extracellular signal molecules must be transported by their receptor across the plasma membrane into the cytosol. (c) A cell-surface receptor capable of binding only one type of signal molecule can mediate only one kind of cell response. (d) Any foreign substance that binds to a receptor for a normal signal molecule will always induce the same response that is produced by that signal molecule on the same cell type.

a) extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor so as to signal a target cell to change its behavior

Intermediate filaments are found mainly in cells that are subject to mechanical stress. Mutations in genes that disrupt intermediate filaments cause some rare human diseases. For example, the skin of people with epidermolysis bullosa simplex is very susceptible to mechanical injury; people with this disorder have mutations in their _______a___________ genes, the intermediate filament found in epithelial cells. These filaments are usually connected from cell to cell through junctions called ________b__________s. The main filaments found in muscle cells belong to the ________c__________ family; people with disruptions in these intermediate filaments can have muscular dystrophy. In the nervous system, ________d__________s help strengthen the extremely long extensions often present in nerve cell axons; disruptions in these intermediate filaments can lead to neurodegeneration. People who carry mutations in the gene for _______e___________, an important protein for cross-linking intermediate filaments, have a disease that combines symptoms of epidermolysis bullosa simplex, muscular dystrophy, and neurodegeneration.

a) keratin b) desmosomes c) vimentin d) neurofilaments e) plectin

Which of the following statements about microtubules is true? (a) Motor proteins move in a directional fashion along microtubules by using the inherent structural polarity of a protofilament. (b) The centromere nucleates the microtubules of the mitotic spindle. (c) Because microtubules are subject to dynamic instability, they are used only for transient structures in a cell. (d) ATP hydrolysis by a tubulin heterodimer is important for controlling the growth of a microtubule.

a) motor proteins move in a directional fashion along microtubules by using the inherent structural polarity of a protofilament

Which of the following statements about molecular switches is false? (a) Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off. (b) Protein kinases transfer the terminal phosphate from ATP onto a protein. (c) Serine/threonine kinases are the most common types of protein kinase. (d) A GTP-binding protein exchanges its bound GDP for GTP to become activated.

a) phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off

Which of the following items below are not important for flagellar movement? (a) sarcoplasmic reticulum (b) ATP (c) dynein (d) microtubules

a) sarcoplasmic reticulum

Activated protein kinase C (PKC) can lead to the modification of the membrane lipids in the vicinity of the active PKC. Figure Q16-30 shows how G proteins can indirectly activate PKC. You have discovered the enzyme activated by PKC that mediates the lipid modification. You call the enzyme Rafty and demonstrate that activated PKC directly phosphorylates Rafty, activating it to modify the plasma membrane lipids in the vicinity of the cell where PKC is active; these lipid modifications can be detected by dyes that bind to the modified lipids. Cells lacking Rafty do not have these modifications, even when PKC is active. Which of the following conditions would lead to signal-independent modification of the membrane lipids by Rafty? (a) the expression of a constitutively active phospholipase C (b) a mutation in the GPCR that binds the signal more tightly (c) a Ca2+ channel in the endoplasmic reticulum with an increased affinity for IP3 (d) a mutation in the gene that encodes Rafty such that the enzyme can no longer be phosphorylated by PKC

a) the expression of a constitutively active phospholipase C

For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; use each word or phrase only once. There are many actin-binding proteins in cells that can bind to actin and modify its activity. Some proteins such as __________A________ bind to actin monomers, sequestering them until needed for filament formation. ___B__________ proteins bind to the end of actin filaments. The ______C_________ proteins are important for nucleation of the branched actin structures commonly found in the _D____ of moving cells, whereas ____E__ proteins are important for the formation of unbranched actin filaments commonly found in ____F____. Proteins belonging to the ___G___ family of GTPases regulate changes in the actin cytoskeleton in response to extracellular signals.

a) thymosin b) capping c) ARP d) lamellipodia e) formin f) filopodia g) Rho

The ethylene response in plants involves a dimeric transmembrane receptor. When the receptor is not bound to ethylene, the receptor binds to and activates a protein kinase, which activates an intracellular signaling pathway that leads to the degradation of a transcriptional regulator important for transcribing the ethylene response genes (see Fig. Q16-50). You discover a phosphatase that is important for ethylene signaling, and you name it PtpE. Plants lacking PtpE never turn on ethylene-response genes, even in the presence of ethylene. You find that PtpE dephosphorylates serine 121 on the transcriptional regulator. Furthermore, plants lacking PtpE degrade the transcriptional regulator in the presence of ethylene. Which of the following statements below is inconsistent with your data? (a) When the transcriptional regulator is phosphorylated, it activates transcription of the ethylene-response genes. (b) When the transcriptional regulator is not phosphorylated, it binds to DNA. (c) Activation of the protein kinase that binds to the ethylene receptor leads to inactivation of PtpE. (d) Binding of ethylene to its receptor leads to the activation of PtpE.

a) when the transcriptional regulator is phosphorylated, it activates transcription of the ethylene-response genes.

The number of distinct protein species found in humans and other organisms can vastly succeed the number of genes. This is largely due to ______________ ______________.

alternative splicing

A. thaliana, or Arabidopsis, is a common weed. Biologists have selected it over hundreds of thousands of other flowering plant species to serve as an experimental model organism because __________________. (a) it can withstand extremely cold climates. (b) it can reproduce in 8-10 weeks. (c) it produces thousands of offspring per plant. (d) Both (b) and (c) are true.

Active transport requires the input of energy into a system so as to move solutes against their electrochemical and concentration gradients. Which of the following is not one of the common ways to perform active transport? (a) Na+ -coupled (b) K+ -coupled (c) ATP-driven (d) light-driven

Although the extracellular environment has a high sodium ion concentration and the intracellular environment has a high potassium ion concentration, both must be neutralized by negatively charged molecules. In the extracellular case, what is the principal anion? (a) HCO3 - (b) Cl- (c) PO4 3- (d) OH-

Because there are four different monomer building blocks that can be used to assemble RNA polymers, the number of possible sequence combinations that can be created for an RNA molecule made of 100 nucleotides is _______. (a) 100 (b) 4^100 (c) 4 × 100 (d) 100/4

Both DNA and RNA are synthesized by covalently linking a nucleoside triphosphate to the previous nucleotide, constantly adding to a growing chain. In the case of DNA, the new strand becomes part of a stable helix. The two strands are complementary in sequence and antiparallel in directionality. What is the principal force that holds these two strands together? (a) ionic interactions (b) hydrogen bonds (c) covalent bonds (d) van der Waals interactions

Brewer's yeast, apart from being an irreplaceable asset in the brewery and in the bakery, is an experimental organism used to study eukaryotic cells. However, it does have some limitations. Which of the processes below cannot be studied in yeast? (a) DNA replication (b) cell motility (c) exocytosis (d) cell division

Which combination of answers best completes the following statement: When atoms are held together by ___________ __________, they are typically referred to as _________. (a) hydrogen bonds, molecules. (b) ionic interactions, salts. (c) ionic interactions, molecules. (d) double bonds, nonpolar.

Ca2+-pumps in the plasma membrane and endoplasmic reticulum are important for _____________. (a) maintaining osmotic balance. (b) preventing Ca2+ from altering the activity of molecules in the cytosol. (c) providing enzymes in the endoplasmic reticulum with Ca2+ ions that are necessary for their catalytic activity. (d) maintaining a negative membrane potential.

Caenorhabditis elegans is a nematode. During its development, it produces more than 1000 cells. However, the adult worm has only 959 somatic cells. The process by which 131 cells are specifically targeted for destruction is called ______________. (a) directed cell pruning. (b) programmed cell death. (c) autophagy. (d) necrosis.

Carbon 14 is an unstable isotope of carbon that decays very slowly. Compared to the common, stable carbon 12 isotope, carbon 14 has two additional ______________. (a) electrons. (b) neutrons. (c) protons. (d) ions.

Catalysts are molecules that lower the activation energy for a given reaction. Cells produce their own catalysts called _____________. (a) proteins. (b) enzymes. (c) cofactors. (d) complexes.

Cells use membranes to help maintain set ranges of ion concentrations inside and outside the cell. Which of the following ions is the most abundant inside a typical mammalian cell? (a) Na+ (b) K+ (c) Ca2+ (d) Cl

Changes in DNA sequence from one generation to the next may result in offspring that are altered in fitness compared with their parents. The process of change and selection over the course of many generations is the basis of __________. (a) mutation. (b) evolution. (c) heredity. (d) reproduction.

Chemical reactions carried out by living systems depend on the ability of some organisms to capture and use atoms from nonliving sources in the environment. The speciﬁc subset of these reactions that break down nutrients in food can be described as _____________. (a) metabolic. (b) catabolic. (c) anabolic. (d) biosynthetic.

Coiled-coils are typically found in proteins that require an elongated structural framework. Which of the following proteins do you expect to have a coiled-coil domain? (a) insulin (b) collagen (c) myoglobin (d) porin

Condensins ________________. (a) are degraded when cells enter M phase. (b) assemble into complexes on the DNA when phosphorylated by M-Cdk. (c) are involved in holding sister chromatids together. (d) bind to DNA before DNA replication begins.

Cytochrome c oxidase is an enzyme complex that uses metal ions to help coordinate the transfer of four electrons to O2. Which metal atoms are found in the active site of this complex? (a) two iron atoms (b) one iron atom and one copper atom (c) one iron atom and one zinc atom (d) one zinc atom and one copper atom

DNA and RNA are different types of nucleic acid polymer. Which of the following is true of DNA but not true of RNA? (a) It contains uracil. (b) It contains thymine. (c) It is single-stranded. (d) It has 5′-to-3′ directionality.

Figure Q12-54 illustrates changes in membrane potential during the formation of an action potential. What membrane characteristic or measurement used to study action potentials is indicated by the arrow (first line)? (a) effect of a depolarizing stimulus (b) resting membrane potential (c) threshold potential (d) action potential

In humans, glycogen is a more useful food-storage molecule than fat because _____________________. (a) a gram of glycogen produces more energy than a gram of fat. (b) it can be utilized to produce ATP under anaerobic conditions, whereas fat cannot. (c) it binds water and is therefore useful in keeping the body hydrated. (d) for the same amount of energy storage, glycogen occupies less space in a cell than does fat

In the electron-transport chain in chloroplasts, ________-energy electrons are taken from __________. (a) high; H2O. (b) low; H2O. (c) high; NADPH. (d) low; NADPH.

In the final step of the citric acid cycle, oxaloacetate is regenerated through the oxidation of malate and this is coupled with the production of which other molecule? (a) FADH (b) NADH (c) GTP (d) CO2

Ion channels are classified as membrane transport proteins. Channels discriminate by size and charge. In addition to Na+ , which one of the following ions would you expect to be able to freely diffuse through a Na+ channel? Explain your answer. (a) Mg2+ (b) H+ (c) K+ (d) Cl-

Which of the following best describes the behavior of a gated channel? (a) It stays open continuously when stimulated. (b) It opens more frequently in response to a given stimulus. (c) It opens more widely as the stimulus becomes stronger. (d) It remains closed if unstimulated.

Living systems are incredibly diverse in size, shape, environment, and behavior. It is estimated that there are between 10 million and 100 million different species. Despite this wide variety of organisms, it remains difficult to define what it means to say something is alive. Which of the following can be described as the smallest living unit? (a) DNA (b) cell (c) organelle (d) protein

NADH contains a high-energy bond that, when cleaved, donates a pair of electrons to the electron-transport chain. What are the immediate products of this bond cleavage? (a) NAD+ + OH- (b) NAD+ + H- (c) NAD- + H+ (d) NAD + H

Osmosis describes the movement of water across a biological membrane and down its concentration gradient. In chemiosmosis, useful energy is harnessed by the cell from the movement of _______________ across the inner mitochondrial membrane into the matrix _________________ a concentration gradient. (a) ATP, against (b) protons, down (c) electrons, down (d) ADP, against

Oxidation is the process by which oxygen atoms are added to a target molecule. Generally, the atom that is oxidized will experience which of the following with respect to the electrons in its outer shell? (a) a net gain (b) a net loss (c) no change (d) an equal sharing

Photosynthesis enables plants to capture the energy from sunlight. In this essential process, plants incorporate the carbon from CO 2 into high-energy __________ molecules, which the plant cell mitochondria use to produce ATP. (a) fat (b) sugar (c) protein (d) fiber

Proteins bind selectively to small-molecule targets called ligands. The selection of one ligand out of a mixture of possible ligands depends on the number of weak, noncovalent interactions in the protein's ligand-binding site. Where is the binding site typically located in the protein structure? (a) on the surface of the protein (b) inside a cavity on the protein surface (c) buried in the interior of the protein (d) forms on the surface of the protein in the presence of ligand

Seed oils are often dehydrogenated and added back into processed foods as partly unsaturated fatty acids. In comparison with the original oil, the new fatty acids have additional double carbon-carbon bonds, replacing what were once single bonds. This process could also be described as _____________. (a) isomerization. (b) oxidation. (c) reduction. (d) protonation.

Select the option that correctly finishes the following statement: "A cell's genome _________________." (a) is defined as all the genes being used to make protein. (b) contains all of a cell's DNA. (c) constantly changes, depending upon the cell's environment. (d) is altered during embryonic development.

Several different classes of enzymes are needed for the catabolism of carbohydrates. Which of the following descriptions best matches the function of a mutase? (a) An enzyme that catalyzes the rearrangement of bonds within a single molecule. (b) An enzyme that catalyzes a change in the position of a specific chemical group within a single molecule. (c) An enzyme that catalyzes the oxidation of a molecule by removing a hydride ion. (d) An enzyme that catalyzes the addition of phosphate groups to other molecules.

Step 6 of the citric acid cycle is catalyzed by succinate dehydrogenase. Keeping in mind that dehydrogenases catalyze redox reactions, which are the products of the reaction in which succinate is oxidized? (a) fumarate, NADH (b) fumarate, FADH2 (c) fumarate, FADH2 (d) succinyl CoA, NADH

Steps 7 and 10 of glycolysis result in substrate-level phosphorylation. Which of the following best describes this process? (a) ATP is being hydrolyzed to phosphorylate the substrate. (b) The energy derived from substrate oxidation is coupled to the conversion of ADP to ATP. (c) Two successive phosphates are transferred, first to AMP, then to ADP, finally forming ATP. (d) The substrate is hydrolyzed using ATP as an energy source.

Studies conducted with a lysozyme mutant that contains an Asp◊Asn change at position 52 and a a in enzymatic Glu◊Gln change at position 35 exhibited almost complete loss activity. What is the most likely explanation for the decrease in enzyme activity in the mutant? (a) increased afﬁnity for substrate (b) absence of negative charges in the active site (c) change in the active-site scaffold (d) larger amino acids in the active site decreases the afﬁnity for substrate

The Nernst equation can be used to calculate the membrane potential based on the ratio of the outer and inner ion concentration. In a resting cell, membrane potential is calculated taking only K+ ions into account. What is V when Co = 15 mM and Ci = 106 mM? (a) 438.1 mV (b) -52.7 mV (c) 52.7 mV (d) -5.3 mV

The activity, the phosphorylation of a protein is typically associated with a change in assembly of a protein complex, or the triggering of a downstream signaling cascade. The addition of ubiquitin, a small polypeptide, is another type of covalent modiﬁcation that can affect the protein function. Ubiquitylation often results in ______________. (a) membrane association. (b) protein degradation. (c) protein secretion. (d) nuclear translocation.

The concentration of H+ ions inside the mitochondrial matrix is lower than it is in the cytosol or the mitochondrial intermembrane space. What would be the immediate effect of a membrane-permeable compound that carries and releases protons into the mitochondrial matrix? (a) inhibition of the electron-transport chain (b) inhibition of ATP synthesis (c) increased import of ADP into the matrix (d) inhibition of the citric acid cycle

The cytoskeleton provides support, structure, motility, and organization, and it forms tracks to direct organelle and vesicle transport. Which of the cytoskeletal elements listed below is the thickest? (a) actin filaments (b) microtubules (c) intermediate filaments (d) none of the above (all the same thickness)

The final metabolite produced by glycolysis is ___________. (a) acetyl CoA. (b) pyruvate. (c) 3-phosphoglycerate. (d) glyceraldehyde 3-phosphate

Which of the following choices best describes the role of the lysosome? (a) transport of material to the Golgi (b) clean-up, recycling, and disposal of macromolecules (c) sorting of transport vesicles (d) the storage of excess macromolecules

Which of the following components of the electron-transport chain does not act as a proton pump? (a) NADH dehydrogenase (b) cytochrome c (c) cytochrome c reductase (d) cytochrome c oxidase

The first energy-generating steps in glycolysis begin when glyceraldehyde 3- phosphate undergoes an energetically favorable reaction in which it is simultaneously oxidized and phosphorylated by the enzyme glyceraldehyde 3- phosphate dehydrogenase to form 1,3-bisphosphoglycerate, with the accompanying conversion of NAD+ to NADH. In a second energetically favorable reaction catalyzed by a second enzyme, the 1,3-bisphosphoglycerate is then converted to 3-phosphoglycerate, with the accompanying conversion of ADP to ATP. Which of the following statements is true about this reaction? (a) The reaction glyceraldehyde 3-phosphate ! 1,3-bisphosphoglycerate should be inhibited when levels of NADH fall. (b) The ΔG° for the oxidation of the aldehyde group on glyceraldehyde 3- phosphate to form a carboxylic acid is more negative than the ΔG° for ATP hydrolysis. (c) The energy stored in the phosphate bond of glyceraldehyde 3-phosphate contributes to driving the reaction forward. (d) The cysteine side chain on the enzyme is oxidized by NAD+

The mitochondrial ATP synthase consists of several different protein subunits. Which subunit binds to ADP + Pi and catalyzes the synthesis of ATP as a result of a conformational change? (a) transmembrane H+ carrier (b) F1 ATPase head (c) peripheral stalk (d) central stalk

The nucleus, an organelle found in eukaryotic cells, confines the __________, keeping them separated from other components of the cell. (a) lysosomes (b) chromosomes (c) peroxisomes (d) ribosomes

The oxygen-dependent reactions required for cellular respiration were originally thought to occur in a linear pathway. By using a competitive inhibitor for one enzyme in the pathway, investigators discovered that these reactions occur in a cycle. Which product in the reaction pathway builds up when the inhibitor is added? (a) citrate (b) succinate (c) fumarate (d) malate

The photosystems in chloroplasts contain hundreds of chlorophyll molecules, most of which are part of _______________. (a) plastoquinone. (b) the antenna complex. (c) the reaction center. (d) the ferredoxin complex

The potential energy stored in high-energy bonds is commonly harnessed when the bonds are split by the addition of _______________ in a process called _____________. (a) ATP, phosphorylation. (b) water, hydrolysis. (c) hydroxide, hydration. (d) acetate, acetylation.

The second law of thermodynamics states that the disorder in any system is always increasing. In simple terms, you can think about dropping NaCl crystals into a glass of water. The solvation and diffusion of ions is favored because there is an increase in _____________. (a) pH. (b) entropy. (c) ions. (d) stored energy.

The simultaneous oxidation and phosphorylation of glyceraldehyde 3-phosphate forms a highly reactive covalent thioester bond between a cysteine side chain (reactive group -SH) on the enzyme (glyceraldehyde 3-phosphate dehydrogenase) and the oxidized intermediate (see arrow in Figure Q13-31A). If the enzyme had a serine (reactive group -OH) instead of a cysteine at this position, which could form only a much-lower-energy bond to the oxidized substrate (see arrow in Figure Q13-31B), how might this new enzyme act? Figure Q13-31 (a) It would oxidize the substrate and phosphorylate it without releasing it. (b) It would oxidize the substrate but not release it. (c) It would phosphorylate the substrate on the 2 position instead of the 1 position. (d) It would behave just like the normal enzyme.

The variations in the physical characteristics between different proteins are inﬂuenced by the overall amino acid compositions, but even more important is the unique amino acid ______________. (a) number. (b) sequence. (c) bond. (d) orientation.

The ﬁrst task you are assigned in your summer laboratory job is to prepare a concentrated NaOH stock solution. The molecular weight of NaOH is 40. How many grams of solid NaOH will you need to weigh out to obtain a 500 mL solution that has a concentration of 10 M? (a) 800 g (b) 200 g (c) 400 g (d) 160 g

To study how proteins fold, scientists must be able to purify the protein of interest, use solvents to denature the folded protein, and observe the process of refolding at successive time the points. What is the effect of the solvents used in denaturation process? (a) The solvents break all covalent interactions. (b) The solvents break all noncovalent interactions. (c) The solvents break some of the noncovalent interactions, resulting in a misfolded protein. (d) The solvents create a new protein conformation.

Two or three α helices can sometimes wrap around each other to form coiled-coils. The stable wrapping of one helix around another is typically driven by ________________ interactions. (a) hydrophilic (b) hydrophobic (c) van der Waals (d) ionic

Ubiquinone is one of two mobile electron carriers in the electron-transport chain. Where does the additional pair of electrons reside in the reduced ubiquinone molecule? (a) The electrons are added directly to the aromatic ring. (b) The electrons are added to each of two ketone oxygens on the aromatic ring. (c) The electrons are added to the hydrocarbon tail, which hides them inside the membrane bilayer. (d) Both electrons, and one proton, are added to a single ketone oxygen bound to the aromatic ring

What is the smallest distance two points can be separated and still resolved using light microscopy? (a) 20 nm (b) 0.2 μm (c) 2 μm (d) 200 μm

When elemental sodium is added to water, the sodium atoms ionize spontaneously. Uncharged Na becomes Na+. This means that the Na atoms have been _____________. (a) protonated. (b) oxidized. (c) hydrogenated. (d) reduced.

When using the Nernst equation to calculate membrane potential, we are making several assumptions about conditions in the cell. Which of the following is not a good assumption? (a) The temperature is 37°C. (b) The plasma membrane is primarily permeable to Na+ . (c) At rest, the interior of the cell is more negatively charged than the exterior. (d) K+ is the principal positive ion in the cell

Which of the following is nota feature commonly observed in βsheets? (a) antiparallel regions (b) coiled-coil patterns (c) extended polypeptide backbone (d) parallel regions

Which of the following is true for a reaction at equilibrium? (a) ΔG = ΔG° (b) ΔG° + RT ln [X]/[Y] = 0 (c) RT ln [X]/[Y] = 0 (d) ΔG + ΔG° = RT ln [X]/[Y]

Which of the following methods would be the most suitable to assess the relative purity of a protein in a sample you have prepared? (a) gel-ﬁltration chromatography (b) gel electrophoresis (c) western blot analysis (d) ion-exchange chromatography

Which of the following monomer building blocks is necessary to assemble selectively permeable boundaries around and inside cells? (a) sugars (b) fatty acids (c) amino acids (d) nucleotides

Which of the following occur without coupling transport of the solute to the movement of a second solute? (a) import of glucose into gut epithelial cells (b) export of Ca2+ from the cytosol (c) export of H+ from animal cells for pH regulation (d) the export of Na+ from cells to maintain resting membrane potential

Which of the following organelles has both an outer and an inner membrane? (a) endoplasmic reticulum (b) mitochondrion (c) lysosome (d) peroxisome

Which of the following polymers of glucose is used as a vehicle to store energy reserves in animal cells? (a) glucagon (b) glycogen (c) starch (d) glycerol

Which of the following statements about "redox potential" is true? (a) Redox potential is a measure of a molecule's capacity to strip electrons from oxygen. (b) For molecules that have a strong tendency to pass along their electrons, the standard redox potential is negative. (c) The transfer of electrons from cytochrome c oxidase to oxygen has a negative redox potential. (d) A molecule's redox potential is a measure of the molecule's capacity to pass along electrons to oxygen

Which of the following statements best reflects the nature of synaptic plasticity? (a) New synapses are created due to the postnatal generation of neurons. (b) Synaptic response changes in magnitude depending on frequency of stimulation. (c) There is a change in the type of neurotransmitter used at the synapse. (d) Neuronal connections are pruned during normal development.

Which of the following statements describes the mitochondrial inner membrane? (a) It is permeable to molecules with molecular mass as high as 5000 daltons. (b) It contains transporters for ATP molecules. (c) It contains proteins that are released during apoptosis. (d) It contains enzymes required for the oxidation of fatty acids.

Which of the following statements is true? (a) The NADH dehydrogenase complex can pump more protons than can the cytochrome b-c1 complex. (b) The pH in the mitochondrial matrix is higher than the pH in the intermembrane space. (c) The proton concentration gradient and the membrane potential across the inner mitochondrial membrane tend to work against each other in driving protons from the intermembrane space into the matrix. (d) The difference in proton concentration across the inner mitochondrial membrane has a much larger effect than the membrane potential on the total proton-motive force

Which of the following statements would not be true of a favorable binding equilibrium? (a) The free-energy change is negative for the system. (b) The concentration of the complex remains lower than the concentration of the unbound components. (c) The complex dissociation rate is slower than the rate for component association. (d) The binding energy for the association is large and negative.

Which of the following types of ion movement might be expected to require cotransport of protons from the mitochondrial intermembrane space to the matrix, inasmuch as it could not be driven by the membrane potential across the inner membrane? (Assume that each ion being moved is moving against its concentration gradient.) (a) import of Ca2+ into the matrix from the intermembrane space (b) import of acetate ions into the matrix from the intermembrane space (c) exchange of Fe2+ in the matrix for Fe3+ in the intermembrane space (d) exchange of ATP from the matrix for ADP in the intermembrane space

Which statement is NOT true about the events/conclusions from studies during the mid-1800s surrounding the discovery of cells? (a) Cells came to be known as the smallest universal building block of living organisms. (b) Scientists came to the conclusion that new cells can form spontaneously from the remnants of ruptured cells. (c) Light microscopy was essential in demonstrating the commonalities between plant and animal tissues. (d) New cells arise from the growth and division of previously existing cells.

Which subatomic particles contribute to the atomic mass for any given element? (a) protons (b) protons and neutrons (c) neutrons (d) protons and electrons

You have generated antibodies that recognize the extracellular domain of the Ca2+-pump. Adding these antibodies to animal cells blocks the active transport of Ca2+ from the cytosol into the extracellular environment. What do you expect to observe with respect to intracellular Ca2+? (a) Ca2+-pumps in vesicle membranes keep cytosolic calcium levels low. (b) Ca2+-pumps in the endoplasmic reticulum membrane keep cytosolic calcium levels low. (c) Ca2+-pumps in the Golgi apparatus keep cytosolic calcium levels low. (d) Ca2+ concentrations in the cytosol increase at a steady rate.

You wish to explore how mutations in specific genes affecting sugar metabolism might alter tooth development. Which organism is likely to provide the best model system for your studies, and why? (a) horses (b) mice (c) E. coli (d) Arabidopsis

Your body extracts energy from the food you ingest by catalyzing reactions that essentially "burn" the food molecules in a stepwise fashion. What is another way to describe this process? (a) reduction (b) oxidation (c) dehydration (d) solvation

Which of the following statements is true? (a) MAP kinase is important for phosphorylating MAP kinase kinase. (b) PI 3-kinase phosphorylates a lipid in the plasma membrane. (c) Ras becomes activated when an RTK phosphorylates its bound GDP to create GTP. (d) STAT proteins phosphorylate JAK proteins, which then enter the nucleus and activate gene transcription.

b) PI 3-kinase phosphorylates a lipid in the plasma membrane

Figure Q16-15 shows the pathway through which nitric oxide (NO) triggers smooth muscle relaxation in a blood-vessel wall. Which of the following situations would lead to relaxation of the smooth muscle cells in the absence of acetylcholine? (a) a smooth muscle cell that has a defect in guanylyl cyclase such that it cannot bind NO (b) a muscle cell that has a defect in guanylyl cyclase such that it constitutively converts GTP to cyclic GMP (c) a muscle cell that has cyclic GMP phosphodiesterase constitutively active (d) a drug that blocks an enzyme involved in the metabolic pathway from arginine to NO

b) a muscle cell that has a defect in guanylyl cyclase such that is constitutively converts GTP to cyclic GMP

The growth factor RGF stimulates proliferation of cultured rat cells. The receptor that binds RGF is a receptor tyrosine kinase called RGFR. Which of the following types of alteration to RGF would be most likely to prevent receptor dimerization? (a) a mutation that increases the affinity of RGFR for RGF (b) a mutation that prevents RGFR from binding to RGF (c) changing the tyrosines that are normally phosphorylated on RGFR dimerization to alanines (d) changing the tyrosines that are normally phosphorylated on RGFR dimerization to glutamic acid

b) a mutation that prevents RGFR from binding to RGF

Male cockroaches with mutations that strongly decrease the function of an RTK called RTKX are oblivious to the charms of their female comrades. This particular RTK binds to a small molecule secreted by sexually mature females. Most males carrying loss-of-function mutations in the gene for Ras protein are also unable to respond to females. You have just read a paper in which the authors describe how they have screened cockroaches that are mutant in RTKX for additional mutations that partly restore the ability of males to respond to females. These mutations decrease the function of a protein that the authors call Z. Which of the following types of protein could Z be? Explain your answer. (a) a protein that activates the Ras protein by causing Ras to exchange GDP for GTP (b) a protein that stimulates hydrolysis of GTP by the Ras protein (c) an adaptor protein that mediates the binding of the RTKX to the Ras protein (d) a transcriptional regulator required for the expression of the Ras gene

b) a protein that stimulates hydrolysis of GTP by the Ras protein

Which of the following statements is false? (a) Cytochalasins prevent actin polymerization. (b) Actin filaments are usually excluded from the cell cortex. (c) Integrins are transmembrane proteins that can bind to the extracellular matrix. (d) ARPs can promote the formation of branched actin filaments.

b) actin filaments are usually excluded from the cell cortex

Which of the following conditions below is likely to decrease the likelihood of skeletal muscle contraction? (a) partial depolarization of the T-tubule membrane, such that the resting potential is closer to zero (b) addition of a drug that blocks Ca2+ binding to troponin (c) an increase in the amount of ATP in the cell (d) a mutation in tropomyosin that decreases its affinity for the actin filament

b) addition of a drug that blocks Ca2+ binding to troponin

Acetylcholine is a signaling molecule that elicits responses from heart muscle cells, salivary gland cells, and skeletal muscle cells. Which of the following statements is false? (a) Heart muscle cells decrease their rate and force of contraction when they receive acetylcholine, whereas skeletal muscle cells contract. (b) Heart muscle cells, salivary gland cells, and skeletal muscle cells all express an acetylcholine receptor that belongs to the transmitter-gated ion channel family. (c) Active acetylcholine receptors on salivary gland cells and heart muscle cells activate different intracellular signaling pathways. (d) Heart muscle cells, salivary gland cells, and skeletal muscle cells all respond to acetylcholine within minutes of receiving the signal.

b) heart muscle cells, salivary glands, and skeletal muscle cells all express an acetylcholine receptor that belongs to the transmitter-gated ion channel family

Which of the following statements about organellar movement in the cell is false? (a) Organelles undergo saltatory movement in the cell. (b) Only the microtubule cytoskeleton is involved in organellar movement. (c) Motor proteins involved in organellar movement use ATP hydrolysis for energy. (d) Organelles are attached to the tail domain of motor proteins.

b) only the microtubule cytoskeleton is involved in organellar movement

Cell lines A and B both survive in tissue culture containing serum but do not proliferate. Factor F is known to stimulate proliferation in cell line A. Cell line A produces a receptor protein (R) that cell line B does not produce. To test the role of receptor R, you introduce this receptor protein into cell line B, using recombinant DNA techniques. You then test all of your various cell lines in the presence of serum for their response to factor F, with the results summarized in Table Q16-1. Which of the following cannot be concluded from your results above? (a) Binding of Factor F to its receptor is required for proliferation of cell line A. (b) Receptor R binds to Factor F to induce cell proliferation in cell line A. (c) Cell line A expresses a receptor for Factor F. (d) Factor F is not required for proliferation in cell line B.

b) receptor R binds to Factor F to induce cell proliferation in cell line A

Which of the following statements about skeletal muscle contraction is false? (a) When a muscle cell receives a signal from the nervous system, voltage-gated channels open in the T-tubule membrane. (b) The changes in voltage across the plasma membrane that occur when a muscle cell receives a signal from the nervous system cause an influx of Ca2+ into the sarcoplasmic reticulum, triggering a muscle contraction. (c) A change in the conformation of troponin leads to changes in tropomyosin such that it no longer blocks the binding of myosin heads to the actin filament. (d) During muscle contraction, the Z discs move closer together as the myosin heads walk toward the plus ends of the actin filaments.

b) the changes in voltage across the plasma membrane that occur when a muscle cell receives a signal from the nervous system cause an influx of Ca2+ into the sarcoplasmic reticulum, triggering a muscle contraction

During the mating process, yeast cells respond to pheromones secreted by other yeast cells. These pheromones bind GPCRs on the surface of the responding cell and lead to the activation of G proteins inside the cell. When a wild-type yeast cell senses the pheromone, its physiology changes in preparation for mating: the cell stops growing until it finds a mating partner. If yeast cells do not undergo the appropriate response after sensing a pheromone, they are considered sterile. Yeast cells that are defective in one or more components of the G protein have characteristic phenotypes in the absence and presence of the pheromone, which are listed in Table 16-27. Which of the following models is consistent with the data from the analysis of these mutants? Explain your answer. (a) α activates the mating response but is inhibited when bound to βγ. (b) βγ activates the mating response but is inhibited when bound to α. (c) The G protein is inactive; either free α or free βγ complex is capable of activating the mating response. (d) The G protein is active; both free α and free βγ complex are required to inhibit the mating response

b) βγ activates the mating response but is inhibited when bound to a

Energy required by the cell is generated in the form of ATP. ATP is hydrolyzed to power many of the cellular processes, increasing the pool of ADP. As the relative amount of ADP molecules increases, they can bind to glycolytic enzymes, which will lead to the production of more ATP. The best way to describe this mechanism of regulation is ___________. (a) feedback inhibition. (b) oxidative phosphorylation. (c) allosteric activation. (d) substrate-level phosphorylation

Antibody production is an indispensible part of our immune response, but it is not the only defense our bodies have. Which of the following is observed during an infection that is not a result of antibody-antigen interactions? (a) B cell proliferation (b) aggregation of viral particles (c) systemic temperature increase (d) antibody secretion

Approximately, how many distinct synapses are established on the dendrites and cell body of a motor neuron in the spinal cord? (a) tens (b) hundreds (c) thousands (d) millions

At the end of DNA replication, the sister chromatids are held together by the ___________. (a) kinetochores. (b) securins. (c) cohesins. (d) histones.

At ﬁrst glance, it may seem that living systems are able to defy the second law of thermodynamics. However, on closer examination, it becomes clear that although cells create organization from raw materials in the environment, they also contribute to disorder in the environment by releasing _____________. (a) water. (b) radiation. (c) heat. (d) proteins.

Bongkrekic acid is an antibiotic that inhibits the ATP/ADP transport protein in the inner mitochondrial membrane. Which of the following will allow electron transport to occur in mitochondria treated with bongkrekic acid? (a) placing the mitochondria in anaerobic conditions (b) adding FADH2 (c) making the inner membrane permeable to protons (d) inhibiting the ATP synthase

Cells use membranes to help maintain set ranges of ion concentrations inside and outside the cell. Which of the following negatively charged ions is not primarily used to buffer positive charges inside the cell? (a) PO4 3- (b) OH- (c) Cl- (d) HCO3-

Chemical reactions that lead to a release of free energy are referred to as "energetically favorable." Another way to describe these reactions is: _____________. (a) uphill. (b) uncatalyzed. (c) spontaneous. (d) activated.

Choose the phrase that best completes this sentence: Microtubules ____________ and are required to pull duplicated chromosomes to opposite poles of dividing cells. (a) generate contractile forces (b) are intermediate in thickness (c) can rapidly reorganize (d) are found in especially large numbers in muscle cells

Double covalent bonds are both shorter and stronger than single covalent bonds, but they also limit the geometry of the molecule because they ____________________. (a) create a new arrangement of electron shells. (b) change the reactivity of the bonded atoms. (c) limit the rotation of the bonded atoms. (d) prevent additional bonds from being formed with the bonded atoms.

Energy cannot be created or destroyed, but it can be converted into other types of energy. Cells use potential kinetic energy to generate stored chemical energy in the form of activated carrier molecules, which are often employed to join two molecules together in _____________ reactions. (a) oxidation (b) hydrolysis (c) condensation (d) reduction

Even though cellular macromolecules contain a large number of carbon and hydrogen atoms, they are not all spontaneously converted into CO2 and H2O. This absence of spontaneous combustion is due to the fact that biological molecules are relatively __________ and an input of energy is required to reach lower energy states. (a) large (b) polar (c) stable (d) unstable

Figure Q12-53 illustrates changes in membrane potential during the formation of an action potential. What membrane characteristic or measurement used to study action potentials is indicated by the arrow (2nd line)? (a) effect of a depolarizing stimulus (b) resting membrane potential (c) threshold potential (d) action potential

Fully folded proteins typically have polar side chains on their surfaces, where electrostatic attractions and hydrogen bonds can form between the polar group on the amino acid and the polar molecules in the solvent. In contrast, some proteins have a polar side chain in their hydrophobic interior. Which of the following would not occur to help accommodate an internal, polar side chain? (a) A hydrogen bond forms between two polar side chains. (b) A hydrogen bond forms between a polar side chain and the protein backbone. (c) A hydrogen bond forms between a polar side chain and an aromatic side chain. (d) Hydrogen bonds form between polar side chains and a buried water molecule.

Glyceraldehyde 3-phosphate dehydrogenase operates by stripping a hydride ion from its substrate. Which molecule is the recipient of the proton and two electrons during this transfer? (a) oxygen (b) acetyl CoA (c) NAD+ (d) FADH

Glycolysis generates more stored energy than it expends. What is the net number of activated carrier molecules produced in this process (number and type of molecules produced minus the number of those molecules used as input)? (a) 6 ATP, 2 NADH (b) 4 ATP, 4 NADH (c) 2 ATP, 2 NADH (d) 4 ATP, 2 NADH

If Na+ channels are opened in a cell that was previously at rest, how will the resting membrane potential be affected? (a) The membrane potential is not affected by Na+ . (b) It becomes more negative. (c) It becomes more positive. (d) It is permanently reset

If the isotope 32S has 16 protons and 16 neutrons, how many protons, neutrons, and electrons will the isotope 35S have, respectively? (a) 16, 20, 15 (b) 16, 19, 15 (c) 16, 19, 16 (d) 16, 19, 17

If you add a compound to illuminated chloroplasts that inhibits the NADP+ reductase, NADPH generation ceases, as expected. However, ferredoxin does not accumulate in the reduced form because it is able to donate its electrons not only to NADP+ (via NADP+ reductase) but also back to the cytochrome b6-f complex. Thus, in the presence of the compound, a "cyclic" form of photosynthesis occurs in which electrons flow in a circle from ferredoxin, to the cytochrome b6-f complex, to plastocyanin, to photosystem I, to ferredoxin. What will happen if you now also inhibit photosystem II? (a) Less ATP will be generated per photon absorbed. (b) ATP synthesis will cease. (c) Plastoquinone will accumulate in the oxidized form. (d) Plastocyanin will accumulate in the oxidized form.

In anaerobic conditions, skeletal muscle produces _____________. (a) lactate and CO2. (b) ethanol and CO2. (c) lactate only. (d) ethanol only.

In oxidative phosphorylation, ATP production is coupled to the events in the electron-transport chain. What is accomplished in the final electron-transfer event in the electron-transport chain? (a) OH- is oxidized to O2 (b) pyruvate is oxidized to CO2 (c) O2 is reduced to H2O (d) NAD+ is reduced to NADH

In step 1 of the citric acid cycle, citrate is generated by the enzyme citrate synthase. The enzyme combines the two-carbon acetyl group from acetyl CoA and the four-carbon oxaloacetate. What is the source of energy that drives this reaction forward? (a) a high-energy phosphodiester bond (b) a transfer of high-energy electrons (c) a high-energy thioester bond (d) the heat of molecular collision

In step 4 of the citric acid cycle, the reduction of NAD+ to NADH is coupled to the generation of CO2 and the formation of a high-energy thioester bond. Which molecule provides the sulfhydryl group necessary to form the thioester bond? (a) pyruvate (b) acetyl CoA (c) CoA (d) cysteine side chain in the catalytic pocket

Mitochondria contain their own genome, are able to duplicate, and actually divide on a different time line from the rest of the cell. Nevertheless, mitochondria cannot function for long when isolated from the cell because they are __________________. (a) viruses. (b) parasites. (c) endosymbionts. (d) anaerobes.

Mitochondria perform cellular respiration, a process that uses oxygen, generates carbon dioxide, and produces chemical energy for the cell. Which answer below indicates a correct pairing of material "burned" and the form of energy produced during cellular respiration? (a) fat, ADP (b) sugar, fat (c) sugar, ATP (d) fat, protein

NADH and FADH2 carry high-energy electrons that are used to power the production of ATP in the mitochondria. These cofactors are generated during glycolysis, the citric acid cycle, and the fatty acid oxidation cycle. Which molecule below can produce the most ATP? Explain your answer. (a) NADH from glycolysis (b) FADH2 from the fatty acid cycle (c) NADH from the citric acid cycle (d) FADH2 from the citric acid cycle

Oxidation and reduction states are relatively easy to determine for metal ions, because there is a measurable net charge. In the case of carbon compounds, oxidation and reduction depend on the nature of polar covalent bonds. Which of the following is the best way to describe these types of bond? (a) hydrogen bonds in a nonpolar solution (b) covalent bonds in an aqueous solution (c) unequal sharing of electrons across a covalent bond (d) equal sharing of electrons across a covalent bond

Oxidative phosphorylation, as it occurs in modern eukaryotes, is a complex process that probably arose in simple stages in primitive bacteria. Which mechanism is proposed to have arisen first as this complex system evolved? (a) electron transfers coupled to a proton pump (b) the reaction of oxygen with an ancestor of cytochrome c oxidase (c) ATP-driven proton pumps (d) the generation of ATP from the energy of a proton gradient

Protein E can bind to two different proteins, S and I. The binding reactions are described by the following equations and values: E + S ◊ ES Keq for ES = 10 E + I ◊ EI Keq for EI = 2 Given the equilibrium constant values, which one of the following statements is true? (a) E binds I more tightly than S. (b) When S is present in excess, no I molecules will bind to E. (c) The binding energy of the ES interaction is greater than that of the EI interaction. (d) Changing an amino acid on the binding surface of I from a basic amino acid to an acidic one will probably make the free energy of association with E more negative

Proteins are important architectural and catalytic components within the cell, helping to determine its chemistry, its shape, and its ability to respond to changes in the environment. Remarkably, all of the different proteins in a cell are made from the same 20 __________. By linking them in different sequences, the cell can make protein molecules with different conformations and surface chemistries, and therefore different functions. (a) nucleotides. (b) sugars. (c) amino acids. (d) fatty acids.

Pyruvate is an important metabolic intermediate that can be converted into several other compounds, depending on which enzyme is catalyzing the reaction. Which of the following cannot be produced from pyruvate in a single enzyme-catalyzed reaction? (a) lactate (b) oxaloacetate (c) citrate (d) alanine

Scientists learned that cell death is a normal and even important part of life by studying the development of the nematode worm C. elegans. What was the most important feature of C. elegans for the study of programmed cell death? (a) The nematode is smaller and simpler than the fruit fly. (b) 70% of C. elegans genes have homologs in humans. (c) The developmental pathway of each cell in the adult worm was known. (d) Its genome was partially sequenced.

Several different classes of enzymes are needed for the catabolism of carbohydrates. Which of the following descriptions best matches the function of a dehydrogenase? (a) An enzyme that catalyzes the rearrangement of bonds within a single molecule. (b) An enzyme that catalyzes a change in the position of a specific chemical group within a single molecule. (c) An enzyme that catalyzes the oxidation of a molecule by removing a hydride ion. (d) An enzyme that catalyzes the addition of phosphate groups to other molecules.

Some cells have aquaporins—channels that facilitate the flow of water molecules through the plasma membrane. For these cells, what regulates the rate and direction of water diffusion across the membrane? (a) aquaporin conformation (b) resting membrane potential (c) solute concentrations on either side of the membrane (d) availability of ATP

Some prokaryotes can live by utilizing entirely inorganic materials. Which of the following inorganic molecules would you predict to be the predominant building block for fats, sugars, and proteins? (a) O 2 (b) N 2 (c) CO 2 (d) H 2

Stage 1 of oxidative phosphorylation requires the movement of electrons along the electron-transport chain coupled to the pumping of protons into the intermembrane space. What is the final result of these electron transfers? (a) OH- is oxidized to O2 (b) pyruvate is oxidized to CO2 (c) O2 is reduced to H2O (d) H- is converted to H2

The Na+ -K+ ATPase is also known as the Na+ -K+ pump. It is responsible for maintaining the high extracellular sodium ion concentration and the high intracellular potassium ion concentration. What happens immediately after the pump hydrolyzes ATP? (a) Na+ is bound (b) ADP is bound (c) the pump is phosphorylated (d) the pump changes conformation

The advantage to the cell of the gradual oxidation of glucose during cellular respiration compared with its combustion to CO2 and H2O in a single step is that ________________. (a) more free energy is released for a given amount of glucose oxidized. (b) no energy is lost as heat. (c) energy can be extracted in usable amounts. (d) more CO2 is produced for a given amount of glucose oxidized.

The enzyme ribulose bisphosphate carboxylase (Rubisco) normally adds carbon dioxide to ribulose 1,5-bisphosphate. However, it will also catalyze a competing reaction in which O2 is added to ribulose 1,5-bisphosphate to form 3- phosphoglycerate and phosphoglycolate. Assume that phosphoglycolate is a compound that cannot be used in any further reactions. If O2 and CO2 have the same affinity for Rubisco, which of the following is the lowest ratio of CO2 to O2 at which a net synthesis of sugar can occur? (a) 1:3 (b) 1:2 (c) 3:1 (d) 2:1

The equilibrium constant (K) for the reaction Y◊X can be expressed with respect to the concentrations of the reactant and product molecules. Which of the expressions below shows the correct relationship between K, [Y], and [X]? (a) K = [Y]/[X] (b) K = [Y] * [X] (c) K = [X]/[Y] (d) K = [X] - [Y]

The equilibrium constant for complex formation between molecules A and B will depend on their relative concentrations, as well as the rates at which the molecules associate and dissociate. The association rate will be larger than the dissociation rate when complex formation is favorable. The energy that drives this process is referred to as ___________. (a) dissociation energy. (b) association energy. (c) binding energy. (d) releasing energy

The intermediates of the citric acid cycle are constantly being depleted because they are used to produce many of the amino acids needed to make proteins. The enzyme pyruvate carboxylase converts pyruvate to oxaloacetate to replenish these intermediates. Bacteria, but not animal cells, have additional enzymes that can carry out the reaction acetyl CoA + isocitrate ! oxaloacetate + succinate. Which of the following compounds will not support the growth of animal cells when used as the major source of carbon in food, but will support the growth of nonphotosynthetic bacteria? (a) pyruvate (b) glucose (c) fatty acids (d) fructose

The reaction cycle that uses acetyl CoA to generate electron carrier molecules needed in the electron-transport chain is important for powering the cell. Which of the names below is not one of those commonly used to describe this reaction cycle? (a) tricarboxylic acid cycle (b) Krebs cycle (c) oxaloacetic acid cycle (d) citric acid cycle

The relationship of free-energy change (ΔG) to the concentrations of reactants and products is important because it predicts the direction of spontaneous chemical reactions. Consider, for example, the hydrolysis of ATP to ADP and inorganic phosphate (Pi). The standard free-energy change (ΔG°) for this reaction is -7.3 kcal/mole. The free-energy change depends on concentrations according to the following equation: ΔG = ΔG° + 1.42 log10 ([ADP] [Pi]/[ATP]) In a resting muscle, the concentrations of ATP, ADP, and Pi are approximately 0.005 M, 0.001 M, and 0.010 M, respectively. At [Pi] = 0.010 M, what will be the ratio of [ATP] to [ADP] at equilibrium? (a) 1.38 × 106 (b) 1 (c) 7.2 × 10-8 (d) 5.14

The small molecule cyclic AMP (cAMP) takes about 0.2 second to diffuse 10 µm, on average, the on one end in a cell. Suppose that cAMP is produced near plasma membrane of the cell; how long will it take for this cAMP to diffuse through the cytosol and reach the opposite end of a very large cell, on average? Assume that the cell is 200 µm in diameter. (a) 4 seconds (b) 16 seconds (c) 80 seconds (d) 200 seconds

When the net charge on either side of the plasma membrane is zero, what else is true? (a) There is an equal number of K+ ions on each side of the plasma membrane. (b) The K+ leak channels are open. (c) The electrochemical potential across the membrane is zero. (d) The resting membrane potential is between -20 mV and -200 mV.

When the polymer X-X-X... is broken down into monomers, it is "phosphorylyzed" rather than hydrolyzed, in the following repeated reaction: X-X-X... + P ◊ X-P + X-X... (reaction 1) Given the ΔG° values of the reactions listed in the following table, what is the expected ratio of X-phosphate (X-P) to free phosphate (P) at equilibrium for reaction 1? (a) 1:10 (b) 1:10 (c) 1:1 (d) 10:1

When there is an excess of nutrients available in the human body, insulin is released to stimulate the synthesis of glycogen from glucose. This is a speciﬁc example of a(n) __________ process, a general process in which larger molecules are made from smaller molecules. (a) metabolic (b) catabolic (c) anabolic (d) biosynthetic

Which of the following gated ion channels are involved in inhibitory synaptic signaling? (a) voltage-gated Na+ channels (b) voltage-gated Ca2+ channels (c) glycine-gated Cl- channels (d) glutamate-gated cation channels

Which of the following is not an electron carrier that participates in the electrontransport chain? (a) cytochrome (b) quinone (c) rhodopsin (d) copper ion

Which of the following is not true of molecular chaperones? (a) They assist polypeptide folding by helping the folding process follow the most energetically favorable pathway. (b) They can isolate proteins from other components of the cells until folding is complete. (c) They can interact with unfolded polypeptides in a way that changes the ﬁnal fold of the protein. (d) They help streamline the protein-folding process by making it a more efﬁcient and reliable process inside the cell.

Which of the following mechanisms best describes the manner in which lysozyme lowers the energy required for its substrate to reach its transition-state conformation? (a) by binding two molecules and orienting them in a way that favors a reaction between them (b) by altering the shape of the substrate to mimic the conformation of the transition state (c) by speeding up the rate at which water molecules collide with the substrate (d) by binding irreversibly to the substrate so that it cannot dissociate

Which of the following methods used to study proteins is limited to proteins with a molecular mass of 50 kD or less? (a) X-ray crystallography (b) ﬁngerprinting (c) nuclear magnetic resonance (d) mass spectroscopy

Which of the following methods would be the most suitable to assess levels of expression of your target protein in different cell types? (a) gel-ﬁltration chromatography (b) gel electrophoresis (c) western blot analysis (d) ion-exchange chromatography

Which of the following reagents are most likely to revitalize your reaction? (a) a vast excess of ATP (b) glucose 6-phosphate and enzyme D (c) creatine phosphate and enzyme A (d) pyrophosphate

Which of the following statements about cytochrome c is true? (a) Cytochrome c shuttles electrons between the NADH dehydrogenase complex and cytochrome c reductase complex. (b) When cytochrome c becomes reduced, two cysteines (sulfur-containing amino acids) become covalently bound to a heme group. (c) The pair of electrons accepted by cytochrome c are added to the porphyrin ring of the bound heme group. (d) Cytochrome c is the last protein in the electron-transport chain, passing its electrons directly to molecular oxygen, a process that reduces O2 to H2O.

Which of the following statements about mitochondrial division is true? (a) Mitochondria divide in synchrony with the cell. (b) The rate of mitochondrial division is the same in all cell types. (c) Mitochondrial division is mechanistically similar to prokaryotic cell division. (d) Mitochondria cannot divide and produce energy for the cell at the same time.

Which of the following statements about resting membrane potential is not true? (a) The resting membrane potential for most animal cells is 0 mV, because the positive and negative ions are in balance. (b) The resting membrane potential for most animal cells is positive, because Na+ ions are so plentiful inside cells. (c) The resting membrane potential for most animal cells is negative, because the inside of the cell is more negatively charged than the outside of the cell. (d) At the resting membrane potential, no ions enter or exit the cell

Which of the following statements describes the mitochondrial intermembrane space? (a) It is permeable to molecules with molecular mass as high as 5000 daltons. (b) It contains transporters for ATP molecules. (c) It contains proteins that are released during apoptosis. (d) It contains enzymes required for the oxidation of fatty acids.

Which of the following statements is true? (a) Disulﬁde bonds are formed by the cross-linking of methionine residues. (b) Disulﬁde bonds are formed mainly in proteins that are retained within the cytosol. (c) Disulﬁde bonds stabilize but do not change a protein's ﬁnal conformation. (d) Agents such as mercaptoethanol can break disulﬁde bonds through oxidation.

Which of the following statements is true? (a) Only compounds with negative redox potentials can donate electrons to other compounds under standard conditions. (b) Compounds that donate one electron have higher redox potentials than those compounds that donate two electrons. (c) The ΔE0′ of a redox pair does not depend on the concentration of each member of the pair. (d) The free-energy change, ΔG, for an electron-transfer reaction does not depend on the concentration of each member of a redox pair

Which of the following statements is true? (a) Peptide bonds are the only covalent bonds that can link together two amino acids in proteins. (b) The polypeptide backbone is free to rotate about each peptide bond. (c) Nonpolar amino acids tend to be found in the interior of proteins. (d) The sequence of the atoms in the polypeptide backbone varies between different proteins.

Which of the following steps or processes in aerobic respiration include the production of carbon dioxide? (a) breakdown of glycogen (b) glycolysis (c) conversion of pyruvate to acetyl CoA (d) oxidative phosphorylation

Which reaction does the enzyme phosphoglucose isomerase catalyze? (a) glucose ! glucose 6-phosphate (b) fructose 6-phosphate ! fructose 1,6-bisphosphate (c) glucose 6-phosphate ! fructose 6-phosphate (d) glucose ! glucose 1-phosphate

Which statement is NOT true about mutations? (a) A mutation is a change in the DNA that can generate offspring less fit for survival than their parents. (b) A mutation can be a result of imperfect DNA duplication. (c) A mutation is a result of sexual reproduction. (d) A mutation is a change in the DNA that can generate offspring that are as fit for survival as their parents are.

Which subatomic particles can vary between isotopes of the same element, without changing the observed chemical properties? (a) electrons (b) protons and neutrons (c) neutrons (d) neutrons and electrons

Zebrafish (Danio rerio) are especially useful in the study of early development because their embryos ______________. (a) are exceptionally large. (b) develop slowly. (c) are transparent. (d) are pigmented.

__________ are fairly small organelles that provide a safe place within the cell to carry out certain biochemical reactions that generate harmful, highly reactive oxygen species. These chemicals are both generated and broken down in the same location. (a) Nucleosomes (b) Lysosomes (c) Peroxisomes (d) Endosomes

Figure Q16-51 shows that intracellular signaling pathways can be highly interconnected. From the information in Figure Q16-51, which of the following statements is incorrect? (a) The GPCR and the RTK both activate phospholipase C. (b) Activation of either the GPCR or the RTK will lead to activation of transcriptional regulators. (c) CaM-kinase is only activated when the GPCR is active and not when the RTK is active. (d) Ras is activated only when the RTK is active and not when the GPCR is active.

c) CaM-kinase is only activated when the GPCR is active and not when the RTK is active

The lab you work in has discovered a previously unidentified extracellular signal molecule called QGF, a 75,000-dalton protein. You add purified QGF to different types of cells to determine its effect on these cells. When you add QGF to heart muscle cells, you observe an increase in cell contraction. When you add it to fibroblasts, they undergo cell division. When you add it to nerve cells, they die. When you add it to glial cells, you do not see any effect on cell division or survival. Given these observations, which of the following statements is most likely to be true? (a) Because it acts on so many diverse cell types, QGF probably diffuses across the plasma membrane into the cytoplasm of these cells. (b) Glial cells do not have a receptor for QGF. (c) QGF activates different intracellular signaling pathways in heart muscles, fibroblasts, and nerve cells to produce the different responses observed. (d) Heart muscle cells, fibroblasts, and nerve cells must all have the same receptor for GQF.

c) QGF activates different intracellular signaling pathways in heart muscles, fibroblasts, and nerve cells to produce the different responses observed

11-52 Which of the following statements about the carbohydrate coating of the cell surface is false? (a) It is not usually found on the cytosolic side of the membrane. (b) It can play a role in cell-cell adhesion. (c) The arrangement of the oligosaccharide side chains is highly ordered, much like the peptide bonds of a polypeptide chain. (d) Specific oligosaccharides can be involved in cell-cell recognition.

c) The arrangement of the oligosaccharide side chains is highly ordered, much like the peptide bonds of a polypeptide chain.

You are interested in how cyclic-AMP-dependent protein kinase A (PKA) functions to affect learning and memory, and you decide to study its function in the brain. It is known that, in the cells you are studying, PKA works via a signal transduction pathway like the one depicted in Figure Q16-28. Furthermore, it is also known that activated PKA phosphorylates the transcriptional regulator called Nerd that then activates transcription of the gene Brainy. Which situation described below will lead to an increase in Brainy transcription? (a) a mutation in the Nerd gene that produces a protein that cannot be phosphorylated by PKA (b) a mutation in the nuclear import sequence of PKA from PPKKKRKV to PPAAAAAV (c) a mutation in the gene that encodes cAMP phosphodiesterase that makes the enzyme inactive (d) a mutation in the gene that encodes adenylyl cyclase that renders the enzyme unable to interact with the α subunit of the G protein

c) a mutation in the gene that encodes cAMP phosphodiesterase that makes the enzyme inactive

The growth factor Superchick stimulates the proliferation of cultured chicken cells. The receptor that binds Superchick is a receptor tyrosine kinase (RTK), and many chicken tumor cell lines have mutations in the gene that encodes this receptor. Which of the following types of mutation would be expected to promote uncontrolled cell proliferation? (a) a mutation that prevents dimerization of the receptor (b) a mutation that destroys the kinase activity of the receptor (c) a mutation that inactivates the protein tyrosine phosphatase that normally removes the phosphates from tyrosines on the activated receptor (d) a mutation that prevents the binding of the normal extracellular signal to the receptor

c) a mutation that inactivates the protein tyrosine phosphatase that normally removes the phosphates from tyrosines on the activated receptor

Figure Q16-52 shows how normal signaling works with a Ras protein acting downstream of an RTK. You examine a cell line with a constitutively active Ras protein that is always signaling. Which of the following conditions will turn off signaling in this cell line? (a) addition of a drug that prevents protein X from activating Ras (b) addition of a drug that increases the affinity of protein Y and Ras (c) addition of a drug that blocks protein Y from interacting with its target (d) addition of a drug that increases the activity of protein Y

c) addition of a drug that blocks protein Y from interacting with its target

Figure Q17-31A shows how the movement of dynein causes the flagellum to bend. If instead of the normal situation, the polarity of the adjacent doublet of microtubules were to be reversed (see Figure Q17-31B) what do you predict would happen? (a) No bending would occur. (b) Bending would occur exactly as diagrammed in Figure Q17-31A. (c) Bending would occur, except that the right microtubule doublet would move down relative to the left one. (d) The two microtubule doublets would slide away from each other.

c) bending would occur, except that the right microtubule doublet would move down relative to the left one

Figure Q17-41 shows the leading edge of a lamellipodium. Which of the following statements is false? (a) Nucleation of new filaments near at the leading edge pushes the plasma membrane forward. (b) ARP proteins nucleate the branched actin filaments in the lamellipodia. (c) Capping proteins bind to the minus end of actin filaments. (d) There is more ATP-bound actin at the leading edge than in the actin filaments away from the leading edge.

c) capping proteins bind to the minus end of actin filaments

You are examining a cell line in which activation of the Rho family member Rac promotes lamellipodia formation. Which of the following statements is most likely to be true? (a) Cells carrying a Rac mutation that makes Rac act as if it is always bound to GTP will polymerize more unbranched actin filaments than normal cells. (b) Cells carrying a Rac mutation that makes Rac unable to exchange GDP for GTP will polymerize more unbranched actin filaments than normal cells. (c) Cells carrying a Rac mutation that makes Rac act as if it is always bound to GTP will polymerize more branched actin filaments than normal cells. (d) Cells carrying a Rac mutation that makes Rac unable to exchange GDP for GTP will polymerize more branched actin filaments than normal cells.

c) cells carrying a Rac mutation that makes Rac act as if it is always bound to GTP will polymerize more branched actin filaments than normal cells

11-23 New membrane phospholipids are synthesized by enzymes bound to the _____________ side of the _________________ membrane. (a) cytosolic, mitochondrial (b) luminal, Golgi (c) cytosolic, endoplasmic reticulum (d) extracellular, plasma

c) cytosolic, endoplasmic reticulum

The local mediator nitric oxide stimulates the intracellular enzyme guanylyl cyclase by ________________. (a) activating a G-protein (b) activating a receptor tyrosine kinase (c) diffusing into cells and stimulating the cyclase directly (d) activating an intracellular protein kinase

c) diffusing into cells and stimulating the cyclase directly

A protein kinase can act as an integrating device in signaling if it ___________________. (a) phosphorylates more than one substrate (b) catalyzes its own phosphorylation (c) is activated by two or more proteins in different signaling pathways (d) initiates a phosphorylation cascade involving two or more protein kinases

c) is activated by two or more proteins in different signaling pathways

Which of the following statements is correct? Kinesins and dyneins ____________________. (a) have tails that bind to the filaments (b) move along both microtubules and actin filaments (c) often move in opposite directions to each other (d) derive their energy from GTP hydrolysis

c) often move in opposite directions to each other

Which of the following structures shorten during muscle contraction? (a) myosin filaments (b) flagella (c) sarcomeres (d) actin filaments

c) sarcomeres

The microtubules in a cell form a structural framework that can have all the following functions except which of the following? (a) holding internal organelles such as the Golgi apparatus in particular positions in the cell (b) creating long thin cytoplasmic extensions that protrude from one side of the cell (c) strengthening the plasma membrane (d) moving materials from one place to another inside a cell

c) strengthening the plasma membrane

The following happens when a cell-surface receptor activates a G protein. (a) The β subunit exchanges its bound GDP for GTP. (b) The GDP bound to the α subunit is phosphorylated to form bound GTP. (c) The α subunit exchanges its bound GDP for GTP. (d) It activates the α subunit and inactivates the βγ complex.

c) the a subunit exchanges its bound GDP for GTP

7-58 The concentration of a particular protein, X, in a normal human cell rises gradually from a low point, immediately after cell division, to a high point, just before cell division, and then drops sharply. The level of its mRNA in the cell remains fairly constant throughout this time. Protein X is required for cell growth and survival, but the drop in its level just before cell division is essential for division to proceed. You have isolated a line of human cells that grow in size in culture but cannot divide, and on analyzing these mutants, you find that levels of X mRNA in the mutant cells are normal. Which of the following mutations in the gene for X could explain these results? (a) the introduction of a stop codon that truncates protein X at the fourth amino acid (b) a change of the first ATG codon to CCA (c) the deletion of a sequence that encodes sites at which ubiquitin can be attached to the protein (d) a change at a splice site that prevents splicing of the RNA

c) the deletion of a sequence that encodes sites at which ubiquitin can be attached to the protein

Place the following in order of size, from the smallest to the largest. A. protofilament B. microtubule C. α-tubulin D. tubulin dimer E. mitotic spindle

c, d, a, b, e

When the neurotransmitter acetylcholine is applied to skeletal muscle cells, it binds the acetylcholine receptor and causes the muscle cells to contract. Succinylcholine, which is a chemical analog of acetylcholine, binds to the acetylcholine receptor on skeletal muscle cells but causes the muscle to relax; it is therefore often used by surgeons as a muscle relaxant. Propose a model for why succinylcholine causes muscle relaxation. What might be the mechanism to explain the different activities of acetylcholine and succinylcholine on the acetylcholine receptor?

conformation states of the receptor alter ion flow

1 Which of the following statements is true? (a) Ubiquinone is a small, hydrophobic protein containing a metal group that acts as an electron carrier. (b) A 2Fe2S iron-sulfur center carries one electron, whereas a 4Fe4S center carries two. (c) Iron-sulfur centers generally have a higher redox potential than do cytochromes. (d) Mitochondrial electron carriers with the highest redox potential generally contain copper ions and/or heme groups.

A chemical reaction is deﬁned as spontaneous if there is a net loss of free energy during the reaction process. However, spontaneous reactions do not always occur rapidly. Favorable biological reactions require ______________ to selectively speed up reactions and meet the demands of the cell. (a) heat (b) ATP (c) ions (d) enzymes

A hungry yeast cell lands in a vat of grape juice and begins to feast on the sugars there, producing carbon dioxide and ethanol in the process: C6H12O6 + 2ADP + 2Pi + H+ ! 2CO2 + 2CH3CH2OH + 2ATP + 2H2O Unfortunately, the grape juice is contaminated with proteases that attack some of the transport proteins in the yeast cell membrane, and the yeast cell dies. Which of the following could account for the yeast cell's demise? (a) toxic buildup of carbon dioxide inside the cell (b) toxic buildup of ethanol inside the cell (c) diffusion of ATP out of the cell (d) inability to import sugar into the cell

Activated carriers are small molecules that can diffuse rapidly and be used to drive biosynthetic reactions in the cell. Their energy is stored in a readily transferable form such as high-energy electrons or chemical groups. Which of the molecules below is the most widely used activated carrier? (a) FADH2 (b) NADH (c) NADPH (d) ATP

Although all protein structures are unique, there are common structural building blocks that are referred to as regular secondary structures. Some proteins have α helices, some have β sheets, and still others have a combination of both. What makes it possible for proteins to have these common structural elements? (a) speciﬁc amino acid sequences (b) side-chain interactions (c) the hydrophobic-core interactions (d) hydrogen bonds along the protein backbone

An ionic bond between two atoms is formed as a result of the ______________. (a) sharing of electrons. (b) loss of electrons from both atoms. (c) loss of a proton from one atom. (d) transfer of electrons from one atom to the other.

Below is a list of breakthroughs in energy metabolism in living systems. Which is the correct order in which they are thought to have evolved? A. H2O-splitting enzyme activity B. light-dependent transfer of electrons from H2S to NADPH C. the consumption of fermentable organic acids D. oxygen-dependent ATP synthesis (a) A, C, D, B (b) C, A, B, D (c) B, C, A, D (d) C, B, A, D

Below is a list of molecules with different chemical characteristics. Knowing that all molecules will eventually diffuse across a phospholipid bilayer, select the option below that most accurately predicts the relative rates of diffusion of these molecules (fastest to slowest). alanine estrogen propanol sodium (a) alanine > propanol > sodium > estrogen (b) sodium > propanol > alanine > estrogen (c) estrogen > propanol > sodium > alanine (d) estrogen > propanol > alanine > sodium

Biologists cannot possibly study all living species. Instead, they try to understand cell behavior by studying a select subset of them. Which of the following characteristics are useful in an organism chosen for use as a model in laboratory studies? (a) amenability to genetic manipulation (b) ability to grow under controlled conditions (c) rapid rate of reproduction (d) all of the above

Both excitatory and inhibitory neurons form junctions with muscles. By what mechanism do inhibitory neurotransmitters prevent the postsynaptic cell from firing an action potential? (a) by closing Na+ channels (b) by preventing the secretion of excitatory neurotransmitters (c) by opening K+ channels (d) by opening Cl- channels

Cell biologists employ targeted fluorescent dyes or modified fluorescent proteins in both standard fluorescence microscopy and confocal microscopy to observe specific details in the cell. Even though fluorescence permits better visualization, the resolving power is essentially the same as that of a standard light microscope because the resolving power of a microscope is limited by the __________ of light. (a) absorption (b) intensity (c) filtering (d) wavelength

Cells make use of H+ electrochemical gradients in many ways. Which of the following proton transporters is used to regulate pH in animal cells? (a) light-driven pump (b) H+ ATPase (c) H+ symporter (d) Na+ -H+ exchanger

Cells require one particular monosaccharide as a starting material to synthesize nucleotide building blocks. Which of the monosaccharides below ﬁlls this important role? (a) glucose (b) fructose (c) ribulose (d) ribose

Chloroplasts are found only in eukaryotic cells that carry out photosynthesis: plants and algae. Plants and algae appear green as a result of the presence of chlorophyll. Where is chlorophyll located in the chloroplast? (a) in the first, outer membrane (b) in the space between the first and second membranes (c) in the second, inner membrane (d) in the third, innermost membrane

Choose the answer that best ﬁts the following statement: Cholesterol is an essential component of biological membranes. Although it is much smaller than the typical phospholipids and glycolipids in the membrane, it is a(n) _________________ molecule, having both hydrophilic and hydrophobic regions. (a) polar (b) oxygen-containing (c) hydrophobic (d) amphipathic

Despite the differences between eukaryotic and prokaryotic cells, prokaryotes have proteins that are distantly related to eukaryotic actin filaments and microtubules. What is likely to be the most ancient function of the cytoskeleton? (a) cell motility (b) vesicle transport (c) membrane support (d) cell division

Electron transport is coupled to ATP synthesis in mitochondria, in chloroplasts, and in the thermophilic bacterium Methanococcus. Which of the following is likely to affect the coupling of electron transport to ATP synthesis in all of these systems? (a) a potent inhibitor of cytochrome c oxidase (b) the removal of oxygen (c) the absence of light (d) an ADP analog that inhibits ATP synthase

Experimental evidence supporting the chemiosmotic hypothesis was gathered by using artificial vesicles containing a protein that can pump protons in one direction across the vesicle membrane to create a proton gradient. Which protein was used to generate the gradient in a highly controlled manner? (a) cytochrome c oxidase (b) NADH dehydrogenase (c) cytochrome c (d) bacteriorhodopsin

Figure Q12-55 illustrates changes in membrane potential during the formation of an action potential. What membrane characteristic or measurement used to study action potentials is indicated by the arrow (from 2nd to top line)? (a) effect of a depolarizing stimulus (b) resting membrane potential (c) threshold potential (d) action potential

If proteins to the dimeric A and B have complementary surfaces, they may interact form complex AB. Which of the following is the correct way to calculate the equilibrium constant for the association between A and B? (a) kon/koff = K (b) K = [A][B]/[AB] (c) K = [AB]/[A][B] (d) (a) and (c)

In a method called patch-clamping, a glass capillary can be converted into a microelectrode that measures the electrical currents across biological membranes. Which of the following is not true about the patch-clamp method? (a) The glass capillary adheres to a "patch" of membrane through the application of suction. (b) The aperture in the glass capillary used to make a microelectrode is about 1 µm in diameter. (c) If the experimental conditions are held constant, fluctuations in electrical currents across the patch of membrane are still observed. (d) Single-channel patch-clamp recordings have demonstrated that gated membrane channels will only open and close in response to specific stimuli.

In step 2 of the citric acid cycle, the enzyme aconitase generates isocitrate from citrate. Which of the following statements about this reaction is true? (a) There is a substantial free-energy difference between the reactants and products of this reaction. (b) The unbonded electrons from hydroxide ions provide energy for this reaction. (c) The aconitase enzyme functions as a mutase in this reaction. (d) The reaction sequence first generates one molecule of water and then consumes one molecule of water.

In the case of a simple conversion reaction such as X◊Y, which value of ΔG° is associated with a larger concentration of X than Y at equilibrium? (Hint: How is ΔG° related to K?) (a) ΔG° = -5 (b) ΔG° = -1 (c) ΔG° = 0 (d) ΔG° = 1

K+ leak channels are found in the plasma membrane. These channels open and close in an unregulated, random fashion. What do they accomplish in a resting cell? (a) They set the K+ concentration gradient to zero. (b) They set the membrane potential to zero. (c) They disrupt the resting membrane potential. (d) They keep the electrochemical gradient for K+ at zero.

Lysozyme is an enzyme that speciﬁcally recognizes bacterial polysaccharides, which renders it an effective antibacterial agent. Into what classiﬁcation of enzymes does lysozyme fall? (a) isomerase (b) protease (c) nuclease (d) hydrolase

Macromolecules in the cell can often interact transiently as a result of noncovalent interactions. These weak interactions also produce stable, highly speciﬁc interactions between molecules. Which of the factors below is the most signiﬁcant in determining whether the interaction will be transient or stable? (a) the size of each molecule (b) the concentration of each molecule (c) the rate of synthesis (d) surface complementarity between molecules

Many types of cells have stores of lipids in their cytoplasm, usually seen as fat droplets. What is the lipid most commonly found in these droplets? (a) cholesterol (b) palmitic acid (c) isoprene (d) triacylglycerol

Molecular chaperones can work by creating an "isolation chamber." What is the purpose of this chamber? (a) The chamber acts as a garbage disposal, degrading improperly folded proteins so that they do not interact with properly folded proteins. (b) This chamber is used to increase the local protein concentration, which will help speed up the folding process. (c) This chamber serves to transport unfolded proteins out of the cell. (d) This chamber serves to protect unfolded proteins from interacting with other proteins in the cytosol, until protein folding is completed.

Motor proteins use the energy in ATP to transport organelles, rearrange elements of the cytoskeleton during cell migration, and move chromosomes during cell division. Which of the following mechanisms is sufﬁcient to ensure the unidirectional movement of a motor protein along its substrate? (a) A conformational change is coupled to the release of a phosphate (Pi). (b) The substrate on which the motor moves has a conformational polarity. (c) A conformational change is coupled to the binding of ADP. (d) A conformational change is linked to ATP hydrolysis.

NADH and NADPH are activated carrier molecules that function in completely different metabolic reactions. Both carry two additional ________ and one additional _____________. This combination can also be referred to as a hydride ion. (a) protons, electron. (b) electrons, phosphate. (c) hydrogens, electron. (d) electrons, proton.

Negatively charged ions are required to balance the net positive charge from metal ions such as K+ , Na+ , and Ca2+. Which of the following negatively charged ions is the most abundant outside the cell and which ion does most often neutralize (written in parentheses)? (a) Cl- (Ca2+) (b) PO4 3- (K+) (c) PO4 3- (Ca2+) (d) Cl- (Na+)

On a diet consisting of nothing but protein, which of the following is the most likely outcome? (a) loss of weight because amino acids cannot be used for the synthesis of fat (b) muscle gain because the amino acids will go directly into building muscle (c) tiredness because amino acids cannot be used to generate energy (d) excretion of more nitrogenous (ammonia-derived) wastes than with a more balanced diet

Photosynthesis is a process that takes place in chloroplasts and uses light energy to generate high-energy electrons, which are passed along an electron-transport chain. Where are the proteins of the electron-transport chain located in chloroplasts? (a) thylakoid space (b) stroma (c) inner membrane (d) thylakoid membrane

Polar covalent bonds are formed when the electrons in the bond are not shared equally between the two nuclei. Which one of these molecules contains polar bonds? (a) molecular oxygen (b) methane (c) propane (d) water

Prokaryotic cells are able to evolve very fast, which helps them to rapidly adapt to new food sources and develop resistance to antibiotics. Which of the options below lists the three main characteristics that support the rapid evolution of prokaryotic populations? (a) microscopic, motile, anaerobic (b) aerobic, motile, rapid growth (c) no organelles, cell wall, can exchange DNA (d) large population, rapid growth, can exchange DNA

Protein structures have several different levels of organization. The primary structure of a protein is its amino acid sequence. The secondary and tertiary structures are more complicated. Consider the deﬁnitions below and select the one that best ﬁts the term "protein domain." (a) a small cluster of α helices and β sheets (b) the tertiary structure of a substrate-binding pocket (c) a complex of more than one polypeptide chain (d) a protein segment that folds independently

Pyruvate can be converted into many other molecules by various biosynthetic and metabolic pathways, which makes it a central hub in the regulation of cellular metabolism. Which of the following molecules is not made from pyruvate? (a) oxaloacetate (b) ethanol (c) lactate (d) NADH

Pyruvate must move from the cytosol into the mitochondria, where it is oxidized to form CO2 and acetyl CoA by the pyruvate dehydrogenase complex. How many different enzymes and what total number of polypeptides, respectively, are required to perform this oxidation process in the mitochondrion? (a) 1; 60 (b) 3; 3 (c) 3; 26 (d) 3; 60

Select the answer that best completes the following statement: Chemical reactions in living systems occur in an ____________ environment, within a narrow range of temperatures. (a) optimal (b) organic (c) extracellular (d) aqueous

Several different classes of enzymes are needed for the catabolism of carbohydrates. Which of the following descriptions best matches the function of a kinase? (a) An enzyme that catalyzes the rearrangement of bonds within a single molecule. (b) An enzyme that catalyzes a change in the position of a specific chemical group within a single molecule. (c) An enzyme that catalyzes the oxidation of a molecule by removing a hydride ion. (d) An enzyme that catalyzes the addition of phosphate groups to other molecules.

Stage 2 of photosynthesis, sometimes referred to as the dark reactions, involves the reduction of CO2 to produce organic compounds such as sucrose. What cofactor is the electron donor for carbon fixation? (a) H2O (b) NADH (c) FADH2 (d) NADPH

Step 3 in glycolysis requires the activity of phosphofructokinase to convert fructose 6-phosphate into fructose 1,6-bisphosphate. Which of the following molecules is an allosteric inhibitor of this enzyme? (a) Pi (b) AMP (c) ADP (d) ATP

The ATP synthase found in chloroplasts is structurally similar to the ATP synthase in mitochondria. Given that ATP is being synthesized in the stroma, where will the F0 portion of the ATP synthase be located? (a) thylakoid space (b) stroma (c) inner membrane (d) thylakoid membrane

The Ras protein is a GTPase that functions in many growth-factor signaling pathways. In its active form, with GTP bound, it transmits a downstream signal that leads to cell proliferation; in its inactive form, with GDP bound, the signal is not transmitted. Mutations in the gene for Ras are found in many cancers. Of the choices below, which alteration of Ras activity is most likely to contribute to the uncontrolled growth of cancer cells? (a) a change that prevents Ras from being made (b) a change that increases the afﬁnity of Ras for GDP (c) a change that decreases the afﬁnity of Ras for GTP (d) a change that decreases the rate of hydrolysis of GTP by Ras

The __________ __________ is made up of two concentric membranes and is continuous with the membrane of the endoplasmic reticulum. (a) plasma membrane (b) Golgi network (c) mitochondrial membrane (d) nuclear envelope

The cell constantly exchanges materials by bringing nutrients in from the external environment and shuttling unwanted by-products back out. Which term describes the process by which external materials are captured inside vesicles and brought into the cell? (a) degradation (b) exocytosis (c) phagocytosis (d) endocytosis

The citric acid cycle is a series of oxidation reactions that removes carbon atoms from substrates in the form of CO2. Once a molecule of acetyl CoA enters the citric acid cycle, how many complete cycles are required for both of the carbon atoms in its acetyl group to be oxidized to CO2? (a) 1 (b) 2 (c) 3 (d) 4

The conversion of fructose 1,6-bisphosphate to fructose 6-phosphate is catalyzed by a fructose 1,6-bisphosphatase and is one of the final steps in gluconeogenesis. Which of the following molecules is an allosteric activator of this enzyme? (a) Pi (b) AMP (c) ADP (d) ATP

The correct folding of proteins is necessary to maintain healthy cells and tissues. Unfolded proteins are responsible for such neurodegenerative disorders as Alzheimer's disease, Huntington's disease, and Creutzfeldt-Jakob disease (the speciﬁc faulty protein is different for each disease). What is the ultimate fate of these disease-causing, unfolded proteins? (a) They are degraded. (b) They bind a different target protein. (c) They form structured ﬁlaments. (d) They form protein aggregates.

The energy used by the cell to generate speciﬁc biological molecules and highly ordered structures is stored in the form of _____________. (a) Brownian motion. (b) heat. (c) light waves. (d) chemical bonds.

The maximum velocity (Vmax) of an enzymatic reaction is an important piece of information regarding how the enzyme works. What series of measurements can be taken in order to infer the maximum velocity of an enzyme-catalyzed reaction? (a) the rate of substrate consumption after the system reaches equilibrium, for several reactant concentrations (b) the rate of product consumption shortly after mixing the enzyme and substrate (c) the rate of substrate consumption at high levels of enzyme concentration (d) the rate of substrate consumption shortly after mixing the enzyme and substrate, for several substrate concentrations

The oxygen-dependent reactions required for cellular respiration were originally thought to occur in a linear pathway. By using a competitive inhibitor for one enzyme in the pathway, investigators discovered that these reactions occur in a cycle. Which enzyme was inhibited? (a) aconitase (b) isocitrate dehydrogenase (c) malate dehydrogenase (d) succinate dehydrogenase

The pH of an aqueous solution is an indication of the concentration of available protons. However, you should not expect to ﬁnd lone protons in solution; rather, the proton is added to a water molecule to form a(n) ______________ ion. (a) hydroxide (b) ammonium (c) chloride (d) hydronium

The relationship of free-energy change (ΔG) to the concentrations of reactants and products is important because it predicts the direction of spontaneous chemical reactions. In the hydrolysis of ATP to ADP and inorganic phosphate (Pi), the standard free-energy change (ΔG°) is -7.3 kcal/mole. The free-energy change depends on concentrations according to the following equation: ΔG = ΔG° + 1.42 log10 ([ADP] [Pi]/[ATP]) In a resting muscle, the concentrations of ATP, ADP, and Pi are approximately 0.005 M, 0.001 M, and 0.010 M, respectively. What is the ΔG for ATP synthesis in resting muscle? (a) -6.01 kcal/mole (b) 5.88 kcal/mole (c) 8.72 kcal/mole (d) 11.1 kcal/mole

The stimulation of auditory nerves depends on the opening and closing of channels in the auditory hair cells. Which type of gating mechanism do these cells use? (a) voltage-gated (b) extracellular ligand-gated (c) intracellular ligand-gated (d) stress-gated

The study of enzyme kinetics is usually performed with puriﬁed components and requires the characterization of several aspects of the reaction, including the rate of association with the substrate, the rate of catalysis, and _____________. (a) the enzyme's structure. (b) the optimal pH of the reaction. (c) the subcellular localization of the enzyme. (d) the regulation of the enzyme activity

What unit of length would you generally use to measure a typical plant or animal cell? (a) centimeters (b) nanometers (c) millimeters (d) micrometers

Which component of the electron-transport chain is required to combine the pair of electrons with molecular oxygen? (a) cytochrome c (b) cytochrome b-c1 complex (c) ubiquinone (d) cytochrome c oxidase

Which of the following characteristics would not support the idea that the ancestral eukaryote was a predator cell that captured and consumed other cells? (a) dynamic cytoskeleton (b) large cell size (c) ability to move (d) rigid membrane

Which of the following is not part of the process known as oxidative phosphorylation? (a) Molecular oxygen serves as a final electron acceptor. (b) FADH2 and NADH become oxidized as they transfer a pair of electrons to the electron-transport chain. (c) The electron carriers in the electron-transport chain toggle between reduced and oxidized states as electrons are passed along. (d) ATP molecules are produced in the cytosol as glucose is converted into pyruvate.

Which of the following is required for the secretion of neurotransmitters in response to an action potential? (a) neurotransmitter receptors (b) Na+ -K+ pumps (c) voltage-gated K+ channels (d) voltage-gated Ca2+ channels

Which of the following processes do not take place in the mitochondria? (a) citric acid cycle (b) conversion of pyruvate to activated acetyl groups (c) oxidation of fatty acids to acetyl CoA (d) glycogen breakdown

Which of the following stages in the breakdown of the piece of toast you had for breakfast generates the most ATP? (a) the digestion of starch to glucose (b) glycolysis (c) the citric acid cycle (d) oxidative phosphorylation

Which of the following statements about GABA receptors is not true? (a) They are located on postsynaptic membranes. (b) They are ligand-gated channels. (c) They inhibit synaptic signaling. (d) They promote neuronal uptake of Na+

Which of the following statements describes the mitochondrial matrix? (a) It is permeable to molecules with molecular mass as high as 5000 daltons. (b) It contains transporters for ATP molecules. (c) It contains proteins that are released during apoptosis. (d) It contains enzymes required for the oxidation of fatty acids.

Which of the following statements does not accurately describe the events involved in the propagation of an action potential? (a) An initial influx of Na+ through a small cluster of channels causes local depolarization of the membrane. (b) Local depolarization causes nearby Na+ channels to open. (c) Channels in depolarized regions of the membrane are inactivated until the resting membrane potential is reestablished. (d) The opening of transmitter-gated K+ channels helps to repolarize the membrane.

Which of the following statements is not true about the possible fates of glyceraldehyde 3-phosphate? (a) It can be exported from the chloroplast to the cytosol for conversion into sucrose. (b) It can be used to make starch, which is stored inside the stroma of the chloroplast. (c) It can be used as a precursor for fatty acid synthesis and stored as fat droplets in the stroma. (d) It can be transported into the thylakoid space for use as a secondary electron acceptor downstream of the electron-transport chain.

Which of the following statements is true? (a) Amoebae have transporter proteins that actively pump water molecules from the cytoplasm to the cell exterior. (b) Bacteria and animal cells rely on the Na+ -K+ pump in the plasma membrane to prevent lysis resulting from osmotic imbalances. (c) The Na+ -K+ pump allows animal cells to thrive under conditions of very low ionic strength. (d) The Na+ -K+ pump helps to keep both Na+ and Cl- ions out of the cell.

Which of the following statements is true? (a) The mitotic spindle is largely made of intermediate filaments. (b) The contractile ring is made largely of microtubules and actin filaments. (c) The contractile ring divides the nucleus in two. (d) The mitotic spindle helps segregate the chromosomes to the two daughter cells.

Which pair of values best fills in the blanks in this statement: On average, eukaryotic cells are __________ times longer and have _________ times more volume than prokaryotic cells. (a) 5, 100 (b) 10, 200 (c) 10, 100 (d) 10, 1000

You have a concentrated stock solution of 10 M NaOH and want to use it to produce a 150 mL solution of 3 M NaOH. What volume of water and stock solutions will you measure out to make this new solution? (a) 135 mL of water, 15 mL of NaOH stock (b) 115 mL of water, 35 mL of NaOH stock (c) 100 mL of water, 50 mL of NaOH stock (d) 105 mL of water, 45 mL of NaOH stock

ΔG measures the change of free energy in a system as it converts reactant (Y) into product (X). When [Y] =[X], ΔG is equal to _____________. (a) ΔG° + RT (b) RT (c) ln [X]/[Y] (d) ΔG°

ΔG° indicates the change in the standard free energy as a reactant is converted to product. Given what you know about these values, which reaction below is the most favorable? (a) ADP + Pi ◊ ATP ΔG° = +7.3 kcal/mole (b) glucose 1-phosphate ◊ glucose 6-phosphate ΔG° = -1.7 kcal/mole (c) glucose + fructose ◊ sucrose ΔG° = +5.5 kcal/mole (d) glucose ◊ CO2 + H2O ΔG° = -686 kcal/mole

β Sheets can participate in the formation of amyloid ﬁbers, which are insoluble protein aggregates. What drives the formation of amyloid ﬁbers? (a) denaturation of proteins containing β sheets (b) extension of β sheets into much longer β strands (c) formation of bioﬁlms by infectious bacteria (d) β-sheet stabilization of abnormally folded proteins

11-58 We can estimate the relative mobility of a population of molecules along the surface of a living cell by fluorescently labeling the molecules of interest, bleaching the label in one small area, and then measuring the speed of signal recovery as molecules migrate back into the bleached area. What is this method called? What does the abbreviation stand for? (a) SDS (b) SPT (c) GFP (d) FRAP

d) FRAP

Adrenaline stimulates glycogen breakdown in skeletal muscle cells by ultimately activating glycogen phosphorylase, the enzyme that breaks down glycogen, as depicted in Figure Q16-29. Which of the following statements below is false? (a) A constitutively active mutant form of PKA in skeletal muscle cells would lead to a decrease in the amount of unphosphorylated phosphorylase kinase. (b) A constitutively active mutant form of PKA in skeletal muscle cells would not increase the affinity of adrenaline for the adrenergic receptor. (c) A constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glucose available. (d) A constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glycogen available.

d) a constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glycogen available

You are interested in understanding the regulation of nuclear lamina assembly. To create an in vitro system for studying this process you start with partly purified nuclear lamina subunits to which you will add back purified cellular components to drive nuclear lamina assembly. Before you start doing experiments, your instructor suggests that you consider what type of conditions would be most amenable to the assembly of nuclear lamina from its individual subunits in vitro. Which of the following conditions do you predict would be most likely to enhance the assembly of the nuclear lamina? (a) addition of phosphatase inhibitors (b) addition of ATP (c) addition of a concentrated salt solution that is 10 times the concentration normally found in the nucleoplasm (d) addition of protein kinase inhibitors

d) addition of protein kinase inhibitors

Consider the in vitro motility assay using purified kinesin and purified polymerized microtubules shown in Figure Q17-50. The three panels are images taken at 1 second intervals. In this figure, three microtubules have been numbered to make it easy to identify them. Which of the following statements about this assay is false? (a) Kinesin molecules are attached by their tails to a glass slide. (b) The microtubules used in this assay must be polymerized using conditions that stabilize tubule formation or else they would undergo dynamic instability. (c) ATP must be added for this assay to work. (d) Addition of the nonhydrolyzable ATP analog (AMP-PNP) would cause the microtubules to move faster.

d) addition of the nonhydrolyzable ATP analog (AMP-PNP) would cause the microtubules to move faster

The hydrolysis of GTP to GDP carried out by tubulin molecules ________________. (a) provides the energy needed for tubulin to polymerize (b) occurs because the pool of free GDP has run out (c) tips the balance in favor of microtubule assembly (d) allows the behavior of microtubules called dynamic instability

d) allows the behavior of microtubules called dynamic instability

Akt promotes the survival of many cells. It is activated by an intracellular signaling pathway that is triggered by an RTK that activates PI 3-kinase, as diagrammed in Figure Q16-48. Which of the following statements is false? (a) In the presence of a survival signal, Akt localizes to the plasma membrane by binding to PIP3. (b) In the absence of survival signal, Bad inhibits the cell death inhibitor protein Bcl2. (c) In the presence of survival signal, the cell death inhibitory protein Bcl2 is active. (d) In the absence of survival signal, Bad is phosphorylated.

d) in the absence of survival signal, Bad is phosphorylated

All members of the steroid hormone receptor family __________________. (a) are cell-surface receptors (b) do not undergo conformational changes (c) are found only in the cytoplasm (d) interact with signal molecules that diffuse through the plasma membrane

d) interact with signal molecules that diffuse through the plasma membrane

Your friend works in a biotech company that has just discovered a drug that seems to promote lamellipodia formation in cells. Which of the following molecules below is unlikely to be involved in the pathway that this drug affects? (a) Rac (b) ARP (c) actin (d) myosin

d) myosin

Keratins, neurofilaments, and vimentins are all categories of intermediate filaments. Which of the following properties below is not true of these types of intermediate filaments? (a) They strengthen cells against mechanical stress. (b) Dimers associate by noncovalent bonding to form a tetramer. (c) They are found in the cytoplasm. (d) Phosphorylation causes disassembly during every mitotic cycle.

d) phosphorylation causes disassembly during every mitotic cycle

Cell movement involves the coordination of many events in the cell. Which of the following phenomena are not required for cell motility? (a) Myosin-mediated contraction at the rear of the moving cell. (b) Integrin association with the extracellular environment. (c) Nucleation of new actin filaments. (d) Release of Ca2+ from the sarcoplasmic reticulum.

d) release of Ca2+ from the sarcoplasmic reticulum

Microtubules are important for transporting cargo in nerve cell axons, as diagrammed in Figure Q17-24. Notice that the two types of cargo are traveling in opposite directions. Which of the following statements is likely to be false? (a) The gray cargo is attached to dynein. (b) The black cargo and the gray cargo require ATP hydrolysis for their motion. (c) The black cargo moving toward the axon terminal contains a domain that specifically interacts with the tail domain of a particular kind of motor. (d) The black cargo and the gray cargo are moving along microtubules of opposite polarity.

d) the black cargo and the gray cargo are moving along microtubules of opposite polarity

Which of the following statements about actin is false? (a) ATP hydrolysis decreases actin filament stability. (b) Actin at the cell cortex helps govern the shape of the plasma membrane. (c) Actin filaments are nucleated at the side of existing actin filaments in lamellipodia. (d) The dynamic instability of actin filaments is important for cell movement.

d) the dynamic instability of actin filaments is important for cell movement

Which of the following statements regarding dynamic instability is false? (a) Each microtubule filament grows and shrinks independently of its neighbors. (b) The GTP cap helps protect a growing microtubule from depolymerization. (c) GTP hydrolysis by the tubulin dimer promotes microtubule shrinking. (d) The newly freed tubulin dimers from a shrinking microtubule can be immediately captured by growing microtubules and added to their plus end.

d) the newly freed tubular dimers from a shrinking microtubule can be immediately captured by growing microtubules and added to their plus end

True or false Most genes in veterbrates are unique and only a few genes are members of multigene families

false

True or false - all tissues are renewed at the same rate.

false

Which of the following is not thought to contribute to diversity in the genome of human individuals?

exon shuffling

1-30 Indicate whether the following statements are true or false. If a statement is false, explain why it is false. A. Lipid-linked proteins are classified as peripheral membrane proteins because the polypeptide chain does not pass through the bilayer.

false

1-30 Indicate whether the following statements are true or false. If a statement is false, explain why it is false. B. A protein can be embedded on the cytosolic side of the membrane bilayer by employing a hydrophobic α helix.

false

1-30 Indicate whether the following statements are true or false. If a statement is false, explain why it is false. D. Membrane proteins that pump ions in and out of the cell are classified as enzymes.

false

1-5 Indicate whether the following statements are true or false. If a statement is false, explain why it is false. B. Phosphatidylserine is the most abundant type of phospholipid found in cell membranes.

false

1-5 Indicate whether the following statements are true or false. If a statement is false, explain why it is false. D. The highly ordered structure of the lipid bilayer makes its generation and maintenance energetically unfavorable.

false

11-43 Indicate whether the following statements are true or false. If a statement is false, explain why it is false. A. When a mouse cell is fused with a human cell, the movement of the respective membrane proteins is restricted to their original locations at the time of fusion.

false

11-43 Indicate whether the following statements are true or false. If a statement is false, explain why it is false. C. The longest carbohydrates found on the surfaces of cells are linked to lipid molecules.

false

11-43 Indicate whether the following statements are true or false. If a statement is false, explain why it is false. D. The only role of the carbohydrate layer on the cell surface is to absorb water, which creates a slimy surface and prevents cells from sticking to each other

false

11-57 Indicate whether the following statements are true or false. If a statement is false, explain why it is false. A. In order to study the activity of isolated transmembrane proteins, the membrane lipids must be completely stripped away.

false

11-57 Indicate whether the following statements are true or false. If a statement is false, explain why it is false. B. FRAP is a method used to study the movement of individual proteins.

false

11-57 Indicate whether the following statements are true or false. If a statement is false, explain why it is false. C. SDS is a mild detergent that is useful for the reconstitution of membrane components.

false

Indicate whether the following statements are true or false. Lysosomes are small organelles where fatty acid synthesis occurs.

false

Indicate whether the following statements are true or false. Plants do not require a cytoskeleton because they have a cell wall that lends structure and support to the cell.

false

Indicate whether the following statements are true or false. The Paramecium is a multicellular microorganism covered with hair-like cilia.

false

Indicate whether the following statements are true or false. The cytosol is fairly empty, containing a limited number of organelles, which allows room for rapid movement via diffusion.

false

Indicate whether the following statements are true or false. The nucleus of an animal cell is round, small, and difficult to distinguish using light microscopy.

false

Indicate whether the following statements are true or false. The number of mitochondria inside a cell remains constant over the life of the cell.

false

Indicate whether the following statements are true or false. The terms "prokaryote" and "bacterium" are synonyms.

false

Indicate whether the following statements are true or false. Photosynthetic bacteria contain chloroplasts.

false

Indicate whether the following statements are true or false. With respect to cellular respiration, the only organelles used by animal cells are mitochondria, while plant cells use both mitochondria and chloroplasts.

false

Indicate whether the following statements are true or false. Mitochondria are thought to have evolved from anaerobic bacteria.

false

True or false Horizontal gene transfer is very rare and this has had little influence on the genomes of bacteria

false

Indicate whether the following statements about enzymes are true or false. If a statement is false, explain why it is false. A. Enzymes alter the equilibrium point of a reaction. B. Vmax can be determined by measuring the amount of product accumulated late in the reaction. C. Competitive inhibitors bind irreversibly to the enzyme active site, lowering Vmax

false false false

Indicate whether a is false, explain the following statements are true or false A. The second law of thermodynamics states that the total amount of energy in the Universe does not change. B. The ultimate source of energy for living systems is chlorophyll. C. CO2 gas is ﬁxed in a series of reactions that are light-dependent. D. H2 is the most stable and abundant form of hydrogen in the environment.

false false false false

Indicate whether the following statements are true or false. If a statement is false, explain why it is false. A. The amino acids in the interior of a protein do not interact with the ligand and do not play a role in selective binding. B. Antibodies are Y-shaped and are composed of six different polypeptide chains. C. ATPases generate ATP for the cell. D. Hexokinase recognizes and phosphorylates only one of the glucose stereoisomers.

false false false true

Indicate whether the following statements are true or false. If a statement is false, explain why it is false. A. Generally, the total number of nonpolar amino acids has a greater effect on protein structure than the exact order of amino acids in a polypeptide chain. B. The "polypeptide backbone" refers to all atoms in a polypeptide chain, except for those that form the peptide bonds. C. The chemical properties of amino acid side chains include charged, uncharged polar, and nonpolar. D. The relative distribution of polar and nonpolar amino acids in a folded protein is determined largely by hydrophobic interactions, which favor the clustering of nonpolar side chains in the interior.

false false true true

Indicate whether the following statements are true or false. A. Primitive plant, animal, and fungal cells probably acquired mitochondria after they diverged from a common ancestor. B. Protozoans are single-celled eukaryotes with cell morphologies and behaviors that can be as complex as those of some multicellular organisms. C. The first eukaryotic cells on Earth must have been aerobic; otherwise, they would not have been able to survive when the planet's atmosphere became oxygen-rich.

false true false

Indicate whether the following statements are true or false. If a statement is false, explain why it is false. A. Van der Waals interactions and hydrophobic interactions are two ways to describe the same type of weak forces that help proteins fold. B. A large number of noncovalent interactions is required to hold two regions of a polypeptide chain together in a stable conformation. C. A single polypeptide tends to adopt 3-4 different conformations, which all have equivalent free-energy values (G).

false true false

Indicate whether the statements below are true or false. If a statement is false, explain why it is false. A. A disaccharide consists of a sugar covalently linked to another molecule such as an amino acid or a nucleotide. B. The hydroxyl groups on monosaccharides are reaction hot spots and can be replaced by other functional groups to produce derivatives of the original sugar. C. The presence of double bonds in the hydrocarbon tail of fatty acid does not greatly inﬂuence its structure.

false true false

Indicate whether the statements below are true or false. If a statement is false, explain why it is false. A. The chemistry of life is carried out and coordinated primarily by the action of small molecules. B. Carbon-based compounds make up the vast majority of molecules found in cells. C. The chemical reactions in living systems are loosely regulated, allowing for a wide range of products and more rapid evolution.

false true false

5-58 Indicate whether the following statements are true or false. If a statement is false, explain why it is false. A. The histone proteins that constitute the core nucleosome include tetramers of histones H2A, H2B, H3, and H4. B. Linker histones help compact genomic DNA by influencing the path of the DNA after it has wrapped about the nucleosome core. C. Histone proteins have a lower-than-average number of lysines and arginines in their polypeptide chains. D. Interphase chromosomes represent a physical state of the chromatin with the highest order of packaging.

false true false false

5-7 Indicate whether the following statements are true or false. If a statement is false, explain why it is false. A. DNA molecules, like proteins, consist of a single, long polymeric chain that is assembled from small monomeric subunits. B. The polarity of a DNA strand results from the polarity of the nucleotide subunits. C. There are five different nucleotides that become incorporated into a DNA strand. D. Hydrogen bonds between each nucleotide hold individual DNA strands together.

false true false false

Indicate whether the following statements are true or false. If a statement is false, explain why it is false. A. Feedback inhibition is deﬁned as a mechanism of down-regulating enzyme activity by the accumulation of a product earlier in the pathway. B. If an enzyme's allosteric binding site is occupied, the enzyme may adopt an alternative conformation that is not optimal for catalysis. C. Protein phosphorylation is another way to alter the conformation of an enzyme and serves exclusively as a mechanism to increase enzyme activity. D. GTP-binding proteins typically have GTPase activity, and the hydrolysis of GTP transforms them to the "off" conformation.

false true false true

Indicate whether the statements below are true or false. If a statement is false, explain why it is false. A. "Nonpolar interactions" is simply another way of saying "van der Waals attractions." B. Condensation reactions occur in the synthesis of all the macromolecules found in cells. C. All proteins and RNAs pass through many unstable conformations as they are folded, ﬁnally settling on one single, preferred conformation.

false true true

Indicate whether the statements below are true or false. If a statement is false, explain why it is false. A. Any covalently bonded H atom can participate in a hydrogen bond if it comes in close proximity with an oxygen atom that forms part of a water molecule. B. Protons are constantly moving between water molecules, which means there is an overall equilibrium between hydroxyl ions and hydronium ions in aqueous solutions. C. A can from strong base is deﬁned as a molecule that readily remove protons water.

false true true

5-42 Indicate whether the following statements are true or false. If a statement is false, explain why it is false. A. Comparing the relative number of chromosome pairs is a good way to determine whether two species are closely related. B. Chromosomes exist at different levels of condensation, depending on the stage of the cell cycle. C. Eukaryotic chromosomes contain many different sites where DNA replication can be initiated. D. The telomere is a specialized DNA sequence where microtubules from the mitotic spindle attach to the chromosome so that duplicate copies move to opposite ends of the dividing cell.

false true true false

Indicate whether the following statements are true or false. If a statement is false, explain why it is false. A. When two macromolecules form a complex, the free energy of the system increases because there is a net increase in the amount of order in the cell. B. Sequential pathways can help drive unfavorable reactions by siphoning off the products into the next energetically favorable reaction in the series. C. The cytosol is densely packed with molecules, creating what is more an aqueous gel than a solution. D. The diffusion rates for smaller molecules in the cytosol are much lower than what is observed for the same molecules in water.

false true true false

Which of the following statements are true or false? If a statement is false, explain why it is false. A. Enzymes lower the free energy released by the reaction that they facilitate. B. Enzymes lower the activation energy for a speciﬁc reaction. C. Enzymes increase the probability that any given reactant molecule will be converted to product. D. Enzymes increase the average energy of reactant molecules

false true true false

Indicate whether the following statements are true or false. If a statement is false, explain why it is false. A. Photosynthetic organisms release only O2 into the atmosphere, while nonphotosynthetic organisms release only CO2. B. The cycling of carbon through the biosphere ﬁrst requires the incorporation of inorganic CO2 into organic molecules. C. The oxidation of one molecule is always coupled to the reduction of a second molecule. D. During cellular respiration, carbon-containing molecules become successively more oxidized until they reach their most oxidized form, as CO2.

false true true true

For each of the following pairs of gene functions, choose the one that is more likely to be highly reserved. A. genes involved in sexual reproduction/genes involved in sugar metabolism B. DNA replication/ developmental pathways C. hormone production/ lipid synthesis

genes involved in sugar metabolism, DNA replication, lipid synthesis

individual 1 is one of the parents of individual 2. The asterisk indicates the occurrence of a single mutation(in the germ line cell of zygote of individual 1). What is the chance that individual 2 will inherit the mutation in individual 1? (a) 100% (b) 50% (c) 1 in 100,000 (d) none

In looking for functionally important nucleotide sequences is it more informative to compare the genome sequences of species M and N or species M and Q?

species M and Q

Describe a mechanism that might drive evolution toward small introns or loss of introns and could account for the evolutionary loss of introns according to the introns early hypothesis.

spontaneous deletion or selection pressure

Phosphorylation of nuclear lamins regulates their assembly and disassembly during mitosis. You add a drug to cells undergoing mitosis that inhibits the activity of an enzyme that dephosphorylates nuclear lamins. What do you predict will happen to these cells? Why?

the cells would become arrested in mitosis. Lamins are typically phosphorylated during mitosis which causes the nuclear envelope to disassemble. Lamins can reassemble at the end of mitosis when they are dephosphorylated. Inhibiting this doesn't allow the laming to reassemble and therefore keeps the cells in mitosis.

1-30 Indicate whether the following statements are true or false. If a statement is false, explain why it is false. C. A protein that relies on protein-protein interactions to stabilize its membrane association is classified as a peripheral membrane protein because it can be dissociated without the use of detergents.

true

1-5 Indicate whether the following statements are true or false. If a statement is false, explain why it is false. A. Although cholesterol is a hydrophobic molecule, it has a hydrophilic head group like all other membrane lipids.

true

1-5 Indicate whether the following statements are true or false. If a statement is false, explain why it is false. C. Glycolipids lack the glycerol component found in phospholipids.

true

11-43 Indicate whether the following statements are true or false. If a statement is false, explain why it is false. B. Epithelial cell membranes are asymmetric, and proteins from the apical side of the cell membrane cannot diffuse into the basal side of the membrane.

true

11-57 Indicate whether the following statements are true or false. If a statement is false, explain why it is false. D. The speed of fluorescent signal recovery during a FRAP assay is a measure of lateral mobility for the molecule of interest.

true

Indicate whether the following statements are true or false. The cytoskeleton is used as a transportation grid for the efficient, directional movement of cytosolic components.

true

Indicate whether the following statements are true or false. Cells of different types can have different chemical requirements.

true

Indicate whether the following statements are true or false. Prokaryotes can adopt several different basic shapes, including spherical, rod-shaped, and spiral.

true

Indicate whether the following statements are true or false. The branchlike extensions that sprout from a single nerve cell in a mammalian brain can extend over several hundred micrometers.

true

Indicate whether the following statements are true or false. The presence of the plasma membrane can be inferred by the well-defined boundary of the cell.

true

Indicate whether the following statements are true or false. Oxygen is toxic to certain prokaryotic organisms.

true

Indicate whether the following statements are true or false. Some prokaryotes have cell walls surrounding the plasma membrane.

true

Indicate whether the following statements are true or false. Thermal energy promotes random movement of proteins, vesicles, and small molecules in the cytosol.

true

Indicate whether the following statements are true or false. Membrane components in the cell are made in the endoplasmic reticulum.

true

Indicate whether the following statements are true or false.. The Golgi apparatus is made up of a series of membrane-enclosed compartments through which materials destined for secretion must pass..

true

True or false A pseudogene is very similar to a functional gene but cannot be expressed because of mutations

true

Indicate whether the statements below are true or false. If a statement is false, explain why it is false. A. Electrons are constantly moving around the nucleus of the atom, but they can move only in discrete regions. B. There is no limit to the number of electrons that can occupy the fourth electron shell. C. Atoms with unﬁlled outer electron shells are especially stable and are therefore less reactive.

true false false

Indicate whether the statements below are true or false. If a statement is false, explain why it is false. A. There are four elements that constitute 99% of all the atoms found in the human body. B. Copper, zinc, and manganese are among 11 nonessential trace elements that contribute less than 0.1% of all the atoms in the human body. C. Approximately 0.9% of the atoms in the human body come from seven essential elements—Na, Mg, K, Ca, P, S, and Cl—all of which form stable ions in aqueous solution.

true false false

5-23 Indicate whether the following statements are true or false. If a statement is false, explain why it is false. A. Each strand of DNA contains all the information needed to create a new double-stranded DNA molecule with the same sequence information. B. All functional DNA sequences inside a cell code for protein products. C. Gene expression is the process of duplicating genes during DNA replication. D. Gene sequences correspond exactly to the respective protein sequences producedfrom them.

true false false false

Indicate whether the statements below are true or false. If a statement is false, explain why it is false. A. Electron shells ﬁll discrete regions around the nucleus of the atom and limit the number of electrons that can occupy a speciﬁc orbit. B. H, C, O, and N are the most common elements in biological molecules because they are the most stable. C. Some atoms are more stable when they lose one or two electrons, even though this means they will have a net positive charge.

true false true

Indicate whether the following statements are true or false. If the statement is false, explain why it is false. A. The human genome is roughly 30 times larger than the Arabidopsis genome, but contains approximately the same number of protein-coding genes. B. The variation in genome size among protozoans is larger than that observed across all species of mammals, birds, and reptiles. C. The vast majority of our genome encodes functional RNA molecules or proteins and most of the intervening DNA is nonfunctional.

true true false

On the basis of the two reactions below, decide which of the following statements are true and which are false. If a statement is false, explain why it is false. 1: ATP + Y ◊ Y-P + ADP ΔG = -100 kcal/mole 2: Y-P + A ◊ B ΔG = 50 kcal/mole A. Reaction 1 is favorable because of the large negative ΔG associated with the hydrolysis of ATP. B. Reaction 2 is an example of an unfavorable reaction. C. Reactions 1 and 2 are coupled reactions, and when they take place together, reaction 2 will proceed in the forward direction. D. Reaction 2 can be used to drive reaction 1 in the reverse direction.

true true true false

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