cell bio final

7-6 Figure Q7-6 shows a ribose sugar. RNA bases are added to the part of the ribose sugar pointed to by arrow _____. (a) 3. (b) 4. (c) 5. (d) 6.

(a) 3.

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) 5′-UGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUG-3′ (c) 5′-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA-3′ (d) 5′-GGAAAAGGAGAUGGGCAAGGGGAAAAGGAGAUGGGCAAGG-3′

(a) 5′-CCCUAAAAAAAAAAAAAAAAUUUUUUUUUUUUUUUUAGGG-3′

13-35 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.

(a) Amino acids can be converted into acetyl CoA.

13-15 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.

(a) An enzyme that catalyzes the rearrangement of bonds within a single molecule.

6-45 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.

(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.

6-44 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) In the deformed mice, somatic cells but not germ cells were mutated. (d) The toxic chemical affects development but is not mutagenic.

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.

13-23 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.

(a) It helps drive the uptake of glucose from outside the cell.

15-14 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.

(a) It is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore.

13-12 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.

(a) It is hydrolyzed to drive the formation of ATP.

15-21 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.

(a) Most peroxisomal proteins are synthesized in the ER.

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.

6-49 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

(a) TTAT

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.

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.

12-59 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

(a) acetylcholine

16-40 You are interested in cell-size regulation and discover that signaling through a GPCR called ERC1 is important in controlling cell size in embryonic rat cells. The G protein downstream of ERC1 activates adenylyl cyclase, which ultimately leads to the activation of PKA. You discover that cells that lack ERC1 are 15% smaller than normal cells, while cells that express a mutant, constitutively activated version of PKA are 15% larger than normal cells. Given these results, which of the following treatments to embryonic rat cells should lead to smaller cells? (a) addition of a drug that causes cyclic AMP phosphodiesterase to be hyperactive (b) addition of a drug that prevents GTP hydrolysis by Gα (c) addition of a drug that activates adenylyl cyclase (d) addition of a drug that mimics the ligand of ERC1

(a) addition of a drug that causes cyclic AMP phosphodiesterase to be hyperactive

16-32 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 Q16-32. Which of the following would enhance this effect of the acetylcholine? Figure Q16-32 (a) addition of a high concentration of a nonhydrolyzable 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 nonhydrolyzable analog of GTP

13-11 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

(a) aldolase

13-27 Select the best option to fill in the blanks of the following statement: 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

(a) anaerobic, pyruvate, ethanol

13-25 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

(a) anaerobically growing yeast

11-50 Consider the apical location of a particular protein expressed in epithelial cells, illustrated in Figure Q11-50A. When a molecule that chelates calcium is added to the cell culture medium, you observe a redistribution of that protein around the entire cell, shown in Figure Q11-50B. Which is most likely to be true about the role of calcium in maintaining an apical distribution of protein A? Figure Q11-50 (a) calcium is required to maintain the structural integrity of the junctional complex (b) calcium is required for the binding of the junctional proteins to the cell cortex (c) calcium is a structural component of protein A (d) calcium inhibits intracellular transport of protein A

(a) calcium is required to maintain the structural integrity of the junctional complex

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.

12-56 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? Figure Q12-56 (a) effect of a depolarizing stimulus (b) resting membrane potential (c) threshold potential (d) action potential

(a) effect of a depolarizing stimulus

15-31 Figure Q15-31 shows the organization of a protein that resides on the ER membrane. The N- and C-termini of the protein are labeled. Boxes 1, 2, and 3 represent membrane-spanning sequences. Non-membrane-spanning regions of the protein are labeled "X," "Y," and "Z." 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

(a) in the cytoplasm

13-2 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

(a) no oxygen is required

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

11-44 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

13-7 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

(a) simple sugars

15-16 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.

(a) sorting sequence, which typically contains the positively charged amino acids lysine and arginine.

15-12 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.

(a) the cytosol.

16-38 Activated protein kinase C (PKC) can lead to the modification of the membrane lipids in the vicinity of the active PKC. Figure Q16-38 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? Figure Q16-38 (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

13-49 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

(a) to generate a molecule of GTP

13-40 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

(a) water

6-48 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

(b) 1/4

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′

15-20 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.

(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.

13-16 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.

(b) An enzyme that catalyzes a change in the position of a specific chemical group within a single molecule.

13-41 Fatty acids can easily be used to generate energy for the cell. Which of the following fatty acids will yield more energy? Explain your answer. (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

(b) CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-COOH

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

13-31 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.

(b) It would oxidize the substrate but not release it.

13-52 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

(b) NADH

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.

12-62 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.

(b) Synaptic response changes in magnitude depending on frequency of stimulation.

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.

15-34 Figure Q15-34 shows the organization of a protein that normally resides in the plasma membrane. The boxes labeled 1 and 2 represent membrane-spanning sequences and the arrow represents a site of action of signal peptidase. Given this diagram, which of the following statements must be true? Figure Q15-34 (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.

(b) The C-terminus of this protein is cytoplasmic.

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.

13-13 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.

(b) The energy derived from substrate oxidation is coupled to the conversion of ADP to ATP.

13-30 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+.

(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.

6-52 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.

(b) Thymine dimers are covalent links between thymidines on opposite DNA strands.

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

6-39 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

(b) base-pair change

13-50 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

(b) fumarate, FADH2

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

13-8 The final metabolite produced by glycolysis is ___________. (a) acetyl CoA. (b) pyruvate. (c) 3-phosphoglycerate. (d) glyceraldehyde 3-phosphate.

(b) pyruvate.

12-54 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? Figure Q12-54 (a) effect of a depolarizing stimulus (b) resting membrane potential (c) threshold potential (d) action potential

(b) resting membrane potential

11-49 Consider the apical location of a particular protein expressed in epithelial cells, illustrated in Figure Q11-49A. Which type of defect described below is the most likely to cause the redistribution of that protein around the entire cell, shown in Figure Q11-49B? Figure Q11-49 (a) a nonfunctional protein glycosylase (b) the deletion of a junctional protein (c) the truncation of a protein found in the extracellular matrix (d) a nonfunctional flippase

(b) the deletion of a junctional protein

16-34 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 16-34. Table Q16-34 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 α

13-9 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

(c) 2 ATP, 2 NADH

7-8 Figure Q7-6 shows a ribose sugar. The part of the ribose sugar where a new ribonucleotide will attach in an RNA molecule is pointed to by arrow ____. (a) 1. (b) 3. (c) 4. (d) 5.

(c) 4.

7-7 Figure Q7-6 shows a ribose sugar. The part of the ribose sugar that is different from the deoxyribose sugar used in DNA is pointed to by arrow ____. (a) 1. (b) 4. (c) 5. (d) 6.

(c) 5.

13-17 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.

(c) An enzyme that catalyzes the oxidation of a molecule by removing a hydride ion.

15-19 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.

(c) Chaperone proteins in the mitochondria facilitate the movement of proteins across the outer and inner mitochondrial membranes.

13-48 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

(c) CoA

7-36 You have discovered a gene (Figure Q7-36A) that is alternatively spliced to produce several forms of mRNA in various cell types, three of which are shown in Figure Q7-36B. The lines connecting the exons that are included in the mRNA indicate the splicing. From your experiments, you know that protein translation begins in exon 1. For all forms of the mRNA, the encoded protein sequence is the same in the regions of the mRNA that correspond to exons 1 and 10. Exons 2 and 3 are alternative exons used in different mRNA, as are exons 7 and 8. Which of the following statements about exons 2 and 3 is the most accurate? Explain your answer. Figure Q7-36 (a) Exons 2 and 3 must have the same number of nucleotides. (b) Exons 2 and 3 must contain an integral number of codons (that is, the number of nucleotides divided by 3 must be an integer). (c) Exons 2 and 3 must contain a number of nucleotides that when divided by 3, leaves the same remainder (that is, 0, 1, or 2). (d) Exons 2 and 3 must have different numbers of nucleotides.

(c) Exons 2 and 3 must contain a number of nucleotides that when divided by 3, leaves the same remainder (that is, 0, 1, or 2).

7-3 Consider two genes that are next to each other on a chromosome, as arranged in Figure Q7-3. Figure Q7-3 Which of the following statements is true? (a) The two genes must be transcribed into RNA using the same strand of DNA. (b) If gene A is transcribed in a cell, gene B cannot be transcribed. (c) Gene A and gene B can be transcribed at different rates, producing different amounts of RNA within the same cell. (d) If gene A is transcribed in a cell, gene B must be transcribed.

(c) Gene A and gene B can be transcribed at different rates, producing different amounts of RNA within the same cell.

13-29 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

(c) NAD+

15-15 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.

(c) Nuclear pores have water-filled passages that small, water-soluble molecules can pass through in a nonselective fashion.

15-18 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.

(c) Nuclear transport receptors would be unable to release their cargo in the nucleus.

15-29 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.

(c) Proteins destined for the ER are translated by cytosolic ribosomes and are targeted to the ER when a signal sequence emerges during translation.

6-51 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

(c) TCT

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.

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.

(c) The transcription of a eukaryotic gene can be influenced by proteins that bind far from the promoter.

16-29 The following happens when a G-protein-coupled 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 α subunit exchanges its bound GDP for GTP.

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.

(c) They have long carbohydrate chains.

13-45 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

(c) a high-energy thioester bond

16-35 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 Q16-35. 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? Figure Q16-35 (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

6-43 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

(c) a nick in the new strand

15-23 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.

(c) begin to cross the membrane while still being synthesized.

13-10 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

(c) conversion of pyruvate to acetyl CoA

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

(c) detergent

15-13 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.

(c) encoded in the amino acid sequence and sufficient for targeting a protein to its correct destination.

13-4 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.

(c) energy can be extracted in usable amounts.

13-22 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

(c) glucose 6-phosphate fructose 6-phosphate

12-66 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

(c) glycine-gated Cl- channels

15-25 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

(c) in the cytosol

6-54 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.

(c) inherited a mutation in a gene required for mismatch repair.

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.

(c) it is single-stranded and can fold up into a variety of structures.

13-26 In anaerobic conditions, skeletal muscle produces _____________. (a) lactate and CO2. (b) ethanol and CO2. (c) lactate only. (d) ethanol only.

(c) lactate only.

13-39 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

(c) oxaloacetic acid cycle

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

(c) proteins are tethered to the proteins on the surface of another cell

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

(c) proteins are tethered to the proteins on the surface of another cell

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.

(c) recognizes promoter sites in the DNA.

12-63 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

(c) thousands

12-53 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? Figure Q12-53 (a) effect of a depolarizing stimulus (b) resting membrane potential (c) threshold potential (d) action potential

(c) threshold potential

6-40 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

(d) 100-fold

13-34 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

(d) 3; 60

13-43 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 groupto be oxidized to CO2? (a) 1 (b) 2 (c) 3 (d) 4

(d) 4

13-47 In step 3 of the citric acid cycle, the oxidation of isocitrate and the production of CO2 are coupled to the reduction of NAD+, generating NADH and an α-ketoglutarate molecule. In the isocitrate molecule shown in Figure Q13-47, which carbon is lost as CO2 and which is converted to a carbonyl carbon? (a) 4 and 6 (b) 6 and 5 (c) 5 and 4 (d) 6 and 4

(d) 6 and 4

16-36 Adrenaline stimulates glycogen breakdown in skeletal muscle cells by ultimately activating glycogen phosphorylase, the enzyme that breaks down glycogen, as depicted in Figure Q16-36. Figure Q16-36 Which of the following statements 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.

13-14 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.

(d) An enzyme that catalyzes the addition of phosphate groups to other molecules.

6-47 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.

(d) Mutations in coding sequences are more likely to be deleterious to the organism than mutations in noncoding sequences.

15-27 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.

(d) Once the signal sequence from Fuzzy has been cleaved, the signal peptide will be ejected into the ER membrane and degraded.

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.

15-28 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.

(d) Some of the proteins in the lumen of the ER can end up in the plasma membrane.

16-30 Which of the following statements about G-protein-coupled receptors (GPCRs) is false? (a) GPCRs are the largest family of cell-surface receptors in humans. (b) GPCRs are used in endocrine, paracrine, and neuronal signaling. (c) GPCRs are found in yeast, mice, and humans. (d) The different classes of GPCR ligands (proteins, amino acid derivatives, or fatty acids) bind to receptors with different numbers of transmembrane domains.

(d) The different classes of GPCR ligands (proteins, amino acid derivatives, or fatty acids) bind to receptors with different numbers of transmembrane domains.

11-56 You have isolated two mutants of a normally pear-shaped microorganism that have lost their distinctive shape and are now round. One of the mutants has a defect in a protein you call A and the other has a defect in a protein you call B. First, you grind up each type of mutant cell and normal cells separately and separate the plasma membranes from the cytoplasm, forming the first cell extract. Then you set aside a portion of each fraction for later testing. Next, you wash the remaining portion of the membrane fractions with a low concentration of urea (which will unfold proteins and disrupt their ability to interact with other proteins) and centrifuge the mixture. The membranes and their constituent proteins form a pellet, and the proteins liberated from the membranes by the urea wash remain in the supernatant. When you check each of the fractions for the presence of A or B, you obtain the results given below. Which of the following statements are consistent with your results (more than one answer may apply)? (a) Protein A is an integral membrane protein that interacts with B, a peripheral membrane protein that is part of the cell cortex. (b) Protein B is an integral membrane protein that interacts with A, a peripheral membrane protein that is part of the cell cortex. (c) Proteins A and B are both integral membrane proteins. (d) The mutation in A affects its ability to interact with B.

(d) The mutation in A affects its ability to interact with B.

12-51 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.

(d) The opening of transmitter-gated K+ channels helps to repolarize the membrane.

13-46 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.

(d) The reaction sequence first generates one molecule of water and then consumes one molecule of water.

12-64 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+.

(d) They promote neuronal uptake of Na+.

7-11 Which of the following statements is false? (a) A new RNA molecule can begin to be synthesized from a gene before the previous RNA molecule's synthesis is completed. (b) If two genes are to be expressed in a cell, these two genes can be transcribed with different efficiencies. (c) RNA polymerase is responsible for both unwinding the DNA helix and catalyzing the formation of the phosphodiester bonds between nucleotides. (d) Unlike DNA, RNA uses a uracil base and a deoxyribose sugar.

(d) Unlike DNA, RNA uses a uracil base and a deoxyribose sugar.

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

12-55 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? Figure Q12-55 (a) effect of a depolarizing stimulus (b) resting membrane potential (c) threshold potential (d) action potential

(d) action potential

11-51 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

15-24 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

(d) all of the above

12-60 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

(d) by opening Cl- channels

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.

13-18 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

(d) excretion of more nitrogenous (ammonia-derived) wastes than with a more balanced diet

13-21 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

(d) glycogen breakdown

15-10 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

(d) in both the cytosol and the chloroplast

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.

13-3 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

(d) oxidative phosphorylation

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

11-41 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

16-31 The length of time a G protein will signal is determined by _______. (a) the activity of phosphatases that turn off G proteins by dephosphorylating Gα. (b) the activity of phosphatases that turn GTP into GDP. (c) the degradation of the G protein after Gαseparates from Gβγ (d) the GTPase activity of Gα

(d) the GTPase activity of Gα

7-20 You have a segment of DNA that contains the following sequence: 5′-GGACTAGACAATAGGGACCTAGAGATTCCGAAA-3′ 3′-CCTGATCTGTTATCCCTGGATCTCTAAGGCTTT-5′ You know that the RNA transcribed from this segment contains the following sequence: 5′-GGACUAGACAAUAGGGACCUAGAGAUUCCGAAA-3′ Which of the following choices best describes how transcription occurs? (a) the top strand is the template strand; RNA polymerase moves along this strand from 5′ to 3′ (b) the top strand is the template strand; RNA polymerase moves along this strand from 3′ to 5′ (c) the bottom strand is the template strand; RNA polymerase moves along this strand from 5′ to 3′ (d) the bottom strand is the template strand; RNA polymerase moves along this strand from 3′ to 5′

(d) the bottom strand is the template strand; RNA polymerase moves along this strand from 3′ to 5′

15-11 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.

(d) transport vesicles.

6-46 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

(d) ultraviolet irradiation damage

12-52 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

(d) voltage-gated Ca2+ channels

6-41 Which of the choices below represents the correct way to repair the mismatch shown in Figure Q6-41? Figure Q6-41 A) B) C) D)

A)

Which of the following statements is true? 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. Ionizing radiation and oxidative damage can cause DNA double-strand breaks.

Which of the following statements is true? 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. 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. C. The longest carbohydrates found on the surfaces of cells are linked to lipid molecules. 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.

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.

Which of the following statements is true? A. Lipid-linked proteins are classified as peripheral membrane proteins because the polypeptide chain does not pass through the bilayer. B. A protein can be embedded on the cytosolic side of the membrane bilayer by employing a hydrophobic α helix. 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. D. Membrane proteins that pump ions in and out of the cell are classified as enzymes.

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.

Which of the following statements is true? A. Neurotransmitters are small molecules released into the synaptic cleft after the fusion of synaptic vesicles with the presynaptic membrane. B. Action potentials are usually mediated by voltage-gated Ca2+ channels. C. Voltage-gated Na+ channels become automatically inactivated shortly after opening, which ensures that the action potential cannot move backward along the axon. D. Voltage-gated K+ channels also open immediately in response to local depolarization, reducing the magnitude of the action potential.

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