test 3
FRAP has revealed that some proteins move in cell membranes much slower than they move in reconstituted liposomes. Which of the following could account for limited mobility of proteins in cell plasma membranes?
All could limit protein mobility.
Replication of a DNA duplex that has undergone depurination can yield a daughter DNA molecule that:
All of the above (contains a mutation in which an incorrect nucleotide has been substituted for the correct one, contains the normal sequence, is missing one nucleotide pair)
A eukaryotic gene is observed to make multiple forms of a protein. How can one eukaryotic gene produce multiple products in the same cell?
Alternative splicing sites can lead to the production of two different mature mRNAs from the same gene, resulting in slightly different proteins.
Translation takes place in a series of four step. Which best describes the four-step cycle?
An aminoacyl-tRNA binds to the vacant A site on the ribosome; a peptide bond is formed; the large subunit of the ribosome translocates, moving the bound tRNAs to the E and P sites; the small subunit of the ribosome translocates, ejecting the tRNA frm the E site
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
The base composition in DNA isolated from cow liver cells is 28% adenine; what percent of the bases are cytosine? A) 14% B) 22% C) 28% D) 36% E) 56%
B) 22%
Which of the following is a fundamental difference between gene regulation in bacteria compared to eukaryotes? A) In bacteria, but not eukaryotes, there is a specific sequence that specifies where RNA polymerase binds and initiates transcription. B) In eukaryotes, but not bacteria, transcription can be influenced by how effectively the DNA sequence of a promoter region interacts with histone octomers. C) Transcription regulation is the most widespread form of control of gene expression in bacteria but not in eukaryotes. D) Gene regulation is readily reversible in eukaryotes but not bacteria.
B) In eukaryotes, but not bacteria, transcription can be influenced by how effectively the DNA sequence of a promoter region interacts with histone octomers.
All the following statements about heterochromatin are true except A) It is a dark-staining area of a chromosome. B) It is usually transcriptionally active. C) It is often simple sequence DNA. D) It is a region of condensed chromatin.
B) It is usually transcriptionally active.
Under which of the following conditions is the Lac operon in Escherichia coli fully turned on? A) Low glucose and lactose levels B) Low glucose but high lactose levels C) High glucose but low lactose levels D) High glucose and lactose levels E) Low cAMP and high glucose levels
B) Low glucose but high lactose levels
Transcription regulation has similarities and differences in bacteria and in eukaryotes. Which of the following is correct in this regard? A) Most bacterial genes are regulated individually, whereas most eukaryotic genes are regulated in clusters. B) The rate of transcription for a eukaryotic gene can vary in a much wider range than for a bacterial gene (which is, at most, only about 1000-fold). C) DNA looping for gene regulation is the rule in bacteria but the exception in eukaryotes. D) Transcription regulators in both bacteria and eukaryotes usually bind directly to RNA polymerase. E) The default state of both bacterial and eukaryotic genomes is transcriptionally active.
B) The rate of transcription for a eukaryotic gene can vary in a much wider range than for a bacterial gene (which is, at most, only about 1000-fold).
Studying the expression of a transcription regulatory protein in two cell types, you have performed experiments showing that the mRNA encoding the protein is present at comparable levels in the cytosol of both cell types. However, based on the expression of its target genes, you suspect that the protein activity might be significantly different in the two cell types. Which of the following steps in expression of the gene encoding this protein is more likely to be differentially controlled in these cell types? A) Transcription B) Translation C) mRNA transport D) mRNA degradation
B) Translation
Nonhomologous end joining is used to A) correct base mismatches in newly synthesized DNA. B) fix double-strand DNA breaks. C) avoid deletion or insertion of bases. D) remove modified or depurinated bases.
B) fix double-strand DNA breaks.
Regulation of transcription by steroid hormones A) involves hormone receptors normally found in the nucleus. B) involves cytoplasmic hormone receptors that can move to the nucleus. C) involves two ligase domains. D) always activates transcription.
B) involves cytoplasmic hormone receptors that can move to the nucleus.
It has been shown that inhibition of a key chromatin remodeling complex known as NuRD, by deleting one of its subunits, can result in a significant increase in the efficiency of reprogramming of somatic cells into pluripotent stem cells. The reprogramming is normally done by the induced expression of a battery of transcription factors in the somatic cells, but is typically not very efficient. Such an observation suggests that the NuRD complex is normally involved in ... A) erasing the epigenetic memory in somatic cells. B) maintaining the epigenetic memory in somatic cells. C) preventing DNA replication. D) formation of extended loops from chromosome territories.
B) maintaining the epigenetic memory in somatic cells.
In RNA interference studies, the double-stranded RNA A) disrupts the target DNA sequence. B) results in the destruction of the target mRNA. C) destroys the target protein. D) all of the above
B) results in the destruction of the target mRNA.
Alteration of histones by addition of methyl and acetyl groups to particular amino acids A) changes B-DNA to Z-DNA. B) results in the remodeling of chromatin that can activate or inhibit gene expression. C) creates G bands seen after Giemsa staining of chromosomes. D) helps preserve telomeres during DNA replication. E) alters the denaturation and renaturation of DNA.
B) results in the remodeling of chromatin that can activate or inhibit gene expression.
You have engineered the X chromosomes in female mice such that one X chromosome expresses green fluorescent protein when active, while the other expresses red fluorescent protein. You have used these mice to study cancer in females. You know that each tumor is a clonal cellular proliferation, meaning all of its proliferating cells are descendants of a single original cancer- causing cell. It follows that, unless X-chromosome inactivation is perturbed in tumors, A) all tumor cells in one mouse should express the same fluorescent protein (either red or green), but tumor cells from different mice can show either red or green fluorescence. B) the cells in any tumor should all express the same fluorescent protein (either red or green), but independently derived tumors in the same mouse can show either green or red fluorescence. C) different cells within each tumor can express different fluorescent proteins, and the tumors would therefore show yellow fluorescence, but each cell shows either red or green fluorescence. D) each cell can express both fluorescent proteins and would therefore emit yellow fluorescence, and the tumors would glow in yellow as well. E) different tumors would show red, yellow, or green fluorescence.
B) the cells in any tumor should all express the same fluorescent protein (either red or green), but independently derived tumors in the same mouse can show either green or red fluorescence.
Which of the following enzymes will produce a blunt end (the cut site is indicated by the * in the recognition sequence)? A) TaqI (T*CGA) B) EagI (C*GGCCG) C) EcoRV (GAT*ATC) D) NsiI (ATGCA*T)
C) EcoRV (GAT*ATC)
Imagine a chromosome translocation event that brings a gene encoding a histone acetyl transferase enzyme from its original chromosomal location to a new one near heterochromatin. Which of the following scenarios is definitely NOT going to happen? A) The gene gets silenced due to heterochromatin expansion, leading to the misregulation of gene expression for a number of critical genes. B) The translocation event also brings along a chromatin barrier that can prevent heterochromatin expansion into the gene, and there is no phenotypic anomaly. C) Since the gene encodes a histone acetyl transferase, it resists heterochromatin expansion by acetylating its own histones. D) The level of the gene product decreases due to a position effect, leading to an imbalance in the chromatin state of the cell that results in the activation of programmed cell death.
C) Since the gene encodes a histone acetyl transferase, it resists heterochromatin expansion by acetylating its own histones.
Which of the following features of DNA underlies its simple replication procedure? A) The fact that it is composed of only four different types of bases B) The antiparallel arrangement of the double helix C) The complementary relationship in the double helix D) The fact that there is a major groove and a minor groove in the double helix
C) The complementary relationship in the double helix
45. Three phospholipids X, Y, and Z are distributed in the plasma membrane as indicated in the figure. For which of these phospholipids does a flippase probably exist? A) X only B) Z only C) X and Y D) Y and Z
C) X and Y
Short micro RNAs (miRNAs) A) code for proteins. B) are common in bacteria but not eukaryotes. C) are involved in regulation of gene expression. D) have no known function.
C) are involved in regulation of gene expression
Splice sites in pre-mRNA are marked by two universally conserved sequences contained A) in the middle of the intron. B) at the ends of the exons. C) at the ends of the introns. D) none of the above
C) at the ends of the introns.
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
Which type of DNA makes up the smallest portion of the human genome? A) introns B) unique noncoding DNA C) exons D) tandemly repeated DNA E) interspersed repeated DNA
C) exons
A gene in a lab is cloned and found to code for a histone methylase enzyme. This enzyme regulates gene expression by?
Condensing the chromatin tighter at the target gene, thereby inhibiting transcription
The TATA box A) serves as a promoter sequence for genes transcribed by RNA polymerase III. B) is located approximately 100 base pairs upstream of the start site for mRNAs. C) is present in all eukaryotic genes. D) acts to position RNA polymerase II for transcription initiation.
D) acts to position RNA polymerase II for transcription initiation.
A DNA sequencing reaction contains which of the following? A) dideoxyribonucleoside triphosphates B) deoxyribonucleoside triphosphates C) DNA polymerase D) all of the above
D) all of the above
Mobile DNA elements likely contributed to the evolution of higher organisms by the A) generation of gene families by gene duplication. B) creation of new genes by exon shuffling. C) formation of more complex regulatory regions. D) all of the above
D) all of the above
Which of the following structures interacts with ribosomes? A) tRNA B) mRNA C) rRNA D) all of the above
D) all of the above
Which of the following is a protein that is involved in translation? A) topoisomerase B) ribosomal RNA C) RNA polymerase D) aminoacyl-tRNA synthetase
D) aminoacyl-tRNA synthetase
In DNA replication, the leading strand of DNA , while the other newly forming strand, called the lagging strand, . A) is synthesized in the 5' --- 3' direction; the new DNA is synthesized in the 3' --- 5' direction B) is synthesized in the 3' --- 5' direction; the new DNA is synthesized in the 5' --- 3' direction C) does not require an RNA primer; an RNA primer is required D) is synthesized as a continuous chain; the new DNA is formed in a series of short, discontinuous fragments E) is synthesized in a series of short, discontinuous fragments; the new DNA is synthesized as a continuous chain
D) is synthesized as a continuous chain; the new DNA is formed in a series of short, discontinuous fragments
The 5' end of a DNA molecule can be chemically distinguished from the 3' end because there is a(n) group at the 5' end and a(n) group at the 3' end. A) amine; carboxyl B) phosphate; sulfate C) hydroxyl; hydrogen D) phosphate; hydroxyl E) amine; hydroxyl
D) phosphate; hydroxyl
Which of the following is not a structural motif found in a DNA-binding domain? A) homeodomain B) zinc-finger C) helix-loop-helix D) random-coil acidic domain
D) random-coil acidic domain
Mismatch repair targets improperly paired nucleotides. The incorrect member of an abnormal base pair can be differentiated from the correct member because A) the incorrect member has undergone a hydroxylation reaction. B) newly synthesized DNA contains uracil. C) the incorrect member doesn't match the surrounding bases. D) the original strand of DNA contains methylated bases while newly synthesized DNA does not; thus the correct member is in the methylated strand. E) the correct member has been deaminated.
D) the original strand of DNA contains methylated bases while newly synthesized DNA does not; thus the correct member is in the methylated strand.
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?
Drosophila DNA contains more origins of replication than E. coli DNA.
What determines the time and place that a certain gene is transcribed in the cell? A) The type of regulatory sequences associated with it B) The relative position of regulatory sequences associated with it C) The arrangement of various regulatory sequences associated with it D) The specific combination of transcription regulators present in the nucleus E) All of the above
E) All of the above
When RNA polymerases were first being characterized, three distinct "peaks" of transcriptional activity were commonly observed when eukaryotic cell extracts were fractioned on chromatography columns... Based on the results shown, what can the researchers conclude about the RNA polymerase?
Eukaryotic cells possess three distinct form of RNA polymerase
A recently isolated bacterial strain has been given to you for general characterization of the genome. You begin by isolating the DNA and subjecting it to thermal denaturation. You use Escherichia coli (E. coli) DNA as a reference. Based on the information in the graph, you can determine that the DNA of the new strain has a high
G-C content with respect to E. coli.
Which statement is true about the association between histone proteins and DNA?
Histone proteins have a high proportion of positively charged amino acids, which tightly bind to the negatively charged backbone
Which of the following is a fundamental difference between gene regulation in bacteria compared to eukaryotes?
In eukaryotes, but not bacteria, transcription can be influenced by how effectively the DNA sequence of a promoter region interacts with histone octomers.
Many antibiotics work by inhibiting bacterial protein synthesis... Based on this observation, which is most likely the mechanism of action of this potentially new antibiotic?
It blocks translocation of the large ribosomal subunit, preventing the movement of peptidyl-tRNA from the A site to the P site of the ribosome
38) A drug added to an in vitro translation mixture containing mRNA molecules with the sequence 5′-AUGAAAAAAAAAAAAUAA-3′ has the following effect: the only product made is a Met-Lys dipeptide that remains attached to the ribosome. What is the most likely way in which the poison acts to inhibit protein synthesis?
It inhibits movement of the small subunit relative to the large subunit.
Which is true of cDNA? (complementary DNA)
It is prepared using mature mRNA transcripts and reverse transcriptase. • cDNA is synthesized from a mRNA template in a reaction catalyzed by the enzymes reverse transcriptase. • Often used to clone eukaryotic genes in prokaryotes
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?
It will be more likely to generate mismatched base pairs
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?
It will be more likely to generate mismatched base pairs.
In humans, three related proteins—heterochromatin protein 1 alpha (HP1[Symbol]), HP1[Symbol], and HP1[Symbol]--are involved in gene silencing. But which histone modifications do these HP1 proteins recognize? To find out, investigators incubated each of the HP1 proteins with three differently modified fragments of the tail of histone H3. One fragment has two methyl groups on lysine (K) residue 9 (K9-Me) ... In this experiment, the peptides are attached to a solid support and the HP1 proteins are mixed with the peptides and allowed to bind. HP1 proteins that do not bind to the peptides are washed away, and the HP1 proteins that are bound are removed and separated on polyacrylamide gel. Antibodies are then used to identify the individual proteins on the gel. As a control, the researchers also included two additional proteins in the experiment: polycomb protein Pc1, which is known to bind to all histone proteins, and Pax 5, a gene regulatory protein that does not bind to any histone proteins. The results of the experiment are shown on the gel below. Based on these results, what conclusions can be made about gene silencing and heterochromatin in human cells?
Methylation of lysine-9 in histone H3 is associated with heterochromatin
In humans and in chimpanzees, 99% of the Alu retrotransposon are in corresponding positions. Which of the following statements below is the most likely explanation for this similarity?
Most of the Alu sequences in the chimpanzee genome underwent duplication and divergence before humans and chimpanzees diverged
You are examining the DNA sequences that encode 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?
Mutations in coding sequences are more likely to be deleterious to the organism than mutations in noncoding sequences
Under which conditions will the lac Z gene be expressed at the highest rate?
No glucose, high lactose
None of the extracts would transform the R-strain cells In the 1940's, Avery, MacLeod, and McCarty performed an experiment demonstrating that DNA is the genetic material. The researchers prepared extracts from a disease-causing S strain of pneumococcus and showed that the "transforming principle" that would permanently change a harmless R strain into an infectious S strain in DNA. Consider the figure, in which an extract from the S-strain cells has been separated into different classes of molecules, each of which is then tested for its ability to transform R-strain cells into S-strain cells. What would the results look like if these fractioned extracts were treated with an enzyme that destroys DNA before they were tested for their ability to transform R cells?
None of the extracts would transform the R-strain cells
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?
Produce lipids with hydrocarbon tails that are shorter and have more double bonds.
To begin transcription, RNA polymerase recognizes nucleotide sequences in what region of the DNA?
Promoter region
Replication origins typically consist of a small stretch of duplex DNA that is relatively easy to pry apart. Which statement is true?
Replication origins are rich in A and T nucleotides
A team of investigators is studying a virus that is believed to have a single replication origin in its genome, which consists of a small circle of double-stranded DNA... Examples of the molecules they see are shown in this diagram. Based on these observations, what is the most likely conclusion to be made about replication in this virus?
Replication proceeds in both directions, from a single origin of replication
A virus called SV40 can generate 100,000 copies of its genome during a single cycle of infection in an animal cell...When this mixture was viewed in an electron microscope, partially unwound structures like the one shown here were observed. Based on this observation, how does T-antigen promote DNA replication?
T-antigen acts as a DNA helicase
For transcription in eukaryotes, either strand of double-stranded DNA may be the template strand. What determines which strand is the template strand?
The base sequence of the promoter (TATA box)
Which of the following descriptions best describes the process of the splicing of a eukaryotic primary RNA transcript?
The exons are linked together, and the introns are removed. This process is driven via two consecutive transesterification reactions between the 2'-hydroxyl of one nucleotide and the 5'-phosphate of another.
You are using restriction sites to determine if your gene of interest was properly incorporated into a plasmid vector. The gene you are working with is a truncated version of a gene that has two restriction sites. The plasmid vector you are working with has one restriction site. When treated with restriction enzymes for the sites and run on a gel, you see 2 bands. What does this imply?
The gene was incorporated into the plasmid, but one of the original gene's restriction sites was in the part of the gene removed to make the truncated version (the truncated gene has only one restriction site.)
Why did DNA evolve to be the carrier of genetic information in cells as opposed to RNA?
The hydrogen at the 2′ position in the deoxyribose of DNA makes it more stable than RNA
If she moves (reference above) the repressor gene (lac I), along with its promoter, to a position at some several thousand base pairs upstream from its normal position, which will you expect to occur?
The lac operon will function normally.
In the mismatch repair process, enzyme complexes replace bases that were incorrectly inserted into the newly synthesized DNA strand. To function, they must be able to distinguish between the parent DNA strand and the new strand. How is this accomplished?
The parent strand is methylated
In an experiment conducted in 1962, investigators took tRNAs bearing cysteine and chemically converted the charged amino acid to an alanine. They then introduced these "hybrid" alanine-bearing tRNAs into a cell-free translation system from which they removed all of the normal, cysteine-bearing tRNAs. How did this chemical manipulation affect the proteins produced by this altered system?
The proteins contained alanines where cysteines were supposed to be
What happens after the DNA polymerase on the lagging-strand template completes an Okazaki fragment?
The sliding clamp attached to the polymerase dissociates from the DNA and the polymerase temporarily releases the lagging-strand template
Suppose an experimenter becomes proficient with a technique that allows her to move DNA sequences within a prokaryotic genome. She decides to use this technique to study the lac operon. If she leaves the promoter in place but moves the operator downstream to the far end of the operon past the three structural genes, which of the following would likely occur when the cell is exposed to lactose?
The structural genes will be transcribed continuously
What is the most likely explanation of why the overall mutation rates in bacteria and in humans are roughly similar?
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.
What would be the most likely result of a prokaryotic species that develops a mutation that allows it to encode for the enzyme telomerase?
There would be no effect on a prokaryote if it developed this mutation.
How do chromatin-remodeling complexes work?
They use the energy from ATP hydrolysis to alter the arrangement of the nucleosomes, rendering certain regions of the DNA more accessible to other proteins
What is the function of the poly-A tail that is added to a eukaryotic mRNA after transcription?
To protect the transcript from degradation by nucleases.
Studying the expression of transcription regulatory protein in two cell types, you have performed experiments showing that the mRNA encoding the protein is present at comparable levels in the cytosol of both cell types... Which of the following steps in expression of the gene encoding this protein is more likely to be differentially controlled in these cell types?
Translation
Proteasomes act primarily on proteins that have been marked for destruction by the covalent attachment of which small protein?
Ubiquitin
Once heterochromatin has been established, it will often spread until it encounters:
a barrier DNA sequence
Which of the following describes a primer used in DNA replication?
a short segment of RNA, about 10 nucleotides in length
What do leucine zippers do during transcription regulation? a) Form hydrogen bonds in the major groove of helices b) Bind to one area of the DNA sequence c) Start the formation complex d) All of the above e) None of the above
a) Form hydrogen bonds in the major groove of helices
34) The figure 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.
a) Polymerase will fill in the staggered end to create a blunt end.
31) DNA that is transcriptionally active? a) is more susceptible to DNase I digestion. b) is tightly packed into a nucleosome arrangement. c) contains unacetylated histones. d) is more condensed than nontranscribed DNA.
a) is more susceptible to DNase I digestion.
In eukaryotes, tandemly repeated genes encode? a) rRNAs. b) cytoskeletal proteins. c) β-globin. d) all of the above
a) rRNAs.
Of the following steps associated with translation, which does not involve hydrolysis of GTP?
aminoacylation of tRNA
Long interspersed nuclear elements (LINEs) found in eukaryotic genomes
are mobile pieces of DNA called transposons that can copy themselves and move around the genome, and they are thought to create genomic variability important to evolutionary adaptation.
Bacterial mRNAs:
are transcribed and translated simultaneously.
Eukaryotic mRNAs:
are translated after they are exported from the nucleus.
The composition of lipids in the outer and inner monolayers of cell membrane lipid bilayers is
asymmetrical; i.e., different in each monolayer.
Which of the following is a fundamental difference between gene regulation in bacteria compared to eukaryotes? a) In bacteria, but not eukaryotes, there is a specific sequence that specifies where RNA polymerase binds and initiates transcription. b) In eukaryotes, but not bacteria, transcription can be influenced by how effectively the DNA sequence of a promoter region interacts with histone octomers. c) Transcription regulation is the most widespread form of control of gene expression in bacteria but not in eukaryotes. d) Gene regulation is readily reversible in eukaryotes but not bacteria.
b) In eukaryotes, but not bacteria, transcription can be influenced by how effectively the DNA sequence of a promoter region interacts with histone octomers.
36. 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.
b) The creation of transgenic pigs that expressed insulin was very expensive compared to the cost of creating bacteria that expressed insulin.
When the ribosome reaches the end of the coding region of an mRNA? a) it releases the polypeptide chain still linked to the last tRNA b) it releases the free polypeptide c) there is a specific tRNA that binds to the termination codon d) All the above
b) it releases the free polypeptide
Unusual eukaryotic-like (possessing a defined nucleus) cells were obtained from a sample of water from a subglacial Antarctic lake. To investigate the properties of the new organism's genome, the nucleus was carefully isolated and the chromatin obtained. The fibers had a "beads on a string" appearance, suggesting some type of "histones." Following digestion with micrococcal nuclease, protein removal, and gel electrophoresis, DNA fragments were obtained that are multiples of 280 base pairs in length. Longer incubation with micrococcal nuclease prior to protein removal results in fragments 200 base pairs in length. The amount of DNA that is wrapped around the "core histones" is therefore
200 base pairs in length.
How many protein coding genes are estimated to be in the human genome?
21,000
The DNA polymerase reaction occurs in the as incoming nucleotides are added to end(s) of the growing DNA chain.
5' → 3' direction; the 3'-hydroxyl
Which of the choices below represents the correct way to repair the mismatch shown in the figure?
A , fix nucleotide
18) When DNA synthesis is initiated at the origin of replication, the two parental strands are replicated? a) In opposite directions b) in same direction c) One continuously and one discontinuously d) A and C are correct
A and C are correct
In a specific DNA sequencing method, di-deoxy-nucleoside-triphosphates (ddNTP's) are involved to produce replicated DNA strands of varying lengths. Once a ddNTP is incorporated into the growing strand of DNA, replication is stopped. Why does the incorporation of a ddNTP in a newly synthesized strand of DNA cease replication?
A ddNTP has no 3' hydroxyl group available to form a phosphodiester bond with the phosphate of the next incoming dNTP
Which best describes the characteristics & function of a 5'-methyl-guanosine cap of a eukaryotic mRNA?
A methylated purine that is added, to the first nucleotide of the transcript to protect the mRNA from degradation by nucleases in the cytoplasm
What evidence suggests that the large amount of excess "junk" DNA in a genome may serve an important function?
A portion of "junk" DNA is highly conserved in its DNA sequence among many different eukaryotic species
The eukaryotic chromosomes are organized inside the nucleus with a huge compaction ratio of several-thousand-fold. What is responsible for such a tight packaging? A) The various chromatin proteins that wrap and fold the DNA B) The nuclear envelope which encapsulates the chromosomes C) The nuclear matrix that provides a firm scaffold D) All of the above
A) The various chromatin proteins that wrap and fold the DNA
The genetic information carried by a cell is passed on, generation after generation, with astonishing fidelity. However, genomes are still altered over evolutionary time scales, and even their overall size can change significantly. Which of the following genome-altering events has increased the size of the mammalian genome the most? A) Transposition B) Point mutation C) Chromosomal deletion D) Chromosomal inversion
A) Transposition
The composition of lipids in the outer and inner monolayers of cell membrane lipid bilayers is A) asymmetrical; i.e., different in each monolayer. B) identical in each monolayer. C) twice as concentrated in the inner monolayer as in the outer monolayer. D) highly random for each monolayer. E) the same for all cell plasma membranes but different from the composition in mitochondrial and chloroplast membranes.
A) asymmetrical; i.e., different in each monolayer.
How does binding of the lac repressor to the lac operator block transcription initiation? A) lac repressor binding blocks RNA polymerase from interacting with DNA at the start site. B) lac repressor binding induces a DNase that cleaves the DNA at the transcription start site. C) lac repressor binding causes a conformational change in RNA polymerase. D) lac repressor binding induces a protease that degrades the sigma subunit of RNA polymerase.
A) lac repressor binding blocks RNA polymerase from interacting with DNA at the start site.
Which of the following is a typical feature of prokaryotic genes? A) polycistronic messenger RNAs B) complex transcription units C) introns D) a and c
A) polycistronic messenger RNAs
RNA editing is A) post-transcriptional alteration of sequences in mRNAs. B) pretranscriptional alteration of sequences in RNAs. C) post-transcriptional joining of two RNA molecules. D) none of the above
A) post-transcriptional alteration of sequences in mRNAs.
DNA replication A) requires a type of RNA polymerase. B) is partially regulated by promoter/terminator sites. C) proceeds by making two continuous strands. D) is not edited once polymerization has occurred. E) is conservative.
A) requires a type of RNA polymerase.
A mutation that changes the recognition sequence for the restriction enzyme EcoRI from GAATTC to GATTTC is an example of a A) single nucleotide polymorphism (SNP). B) simple sequence repeat (SSR). C) a and b D) all of the above
A) single nucleotide polymorphism (SNP).
Thymine is used in DNA despite the fact that it is energetically more expensive to synthesize than uracil because A) spontaneous deamination reactions convert cytosine to uracil at a fairly high rate. B) uracil is more sensitive to ultraviolet (UV) damage. C) uracil is more susceptible to depurination. D) uracil can only bind with ribose, not deoxyribose. E) thymine is less likely to undergo spontaneous deamination than uracil.
A) spontaneous deamination reactions convert cytosine to uracil at a fairly high rate.
An enzyme that breaks DNA, dispels the tension, and reseals the strand ahead of a DNA replication growing fork is called a(n) A) topoisomerase. B) DNA polymerase. C) phosphodiesterase. D) aminoacyl-tRNA synthetase.
A) topoisomerase.
35. 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.
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.
DNA polymerase proofreading results in...? a) dissociation of replication complex from the DNA if a mistake has been made. b) cleavage of the template strand. c) removal of a mismatched base and its replacement by the correct base. d) daughter DNA being discarded and the process starting over from the beginning.
c) removal of a mismatched base and its replacement by the correct base.
What characteristic is shared between most prokaryotic and mitochondrial genomes?
circular chromosomes
Which of the following is not a reason for the importance of mRNA processing in eukaryotes?
coupling of transcription and translation
New membrane phospholipids are synthesized by enzymes bound to the side of the membrane? a) cytosolic; endoplasmic reticulum b) extracellular; plasma c) luminal; extracellular d) cytosolic; plasma
cytosolic; endoplasmic reticulum
Cells preserve their identity after cell division with which of the following? a) DNA methylation b) Remembered positive feedback loops c) Maintenance of chromatin structure d) All of the above
d) All of the above
You are preparing to make a genomic DNA library from yeast. Which of the following enzymes do you need? a) DNase b) DNA Polymerase c) RNA Polymerase d) Restriction endonuclease e) Reverse transcriptase
d) Restriction endonuclease
SINES (short interspersed nuclear elements)? a) are approximately 300 base pairs long. b) are LTR (long terminal repeats) containing retrotransposons. c) are present in over 1 million copies in the human genome. d) a and c
d) a and c
28) Which of the following is a protein that is involved in translation? a) topoisomerase b) ribosomal RNA c) RNA polymerase d) aminoacyl-tRNA synthetase
d) aminoacyl-tRNA synthetase
What is the function of topoisomerase I ? a) to relieve torsional stress in nuclear DNA during replication b) to splice together exons during transcription c) to remove DNA supercoils during transcription d) both a and c
d) both a and c
Chloramphenicol blocks the peptidyl transferase reaction on ribosomes. Which of the following processes are inhibited? a) splicing b) 5' end capping c) base excision repair d) protein elongation
d) protein elongation
33) Which of the following is not a structural motif found in a DNA-binding domain? a) homeodomain b) zinc-finger c) helix-loop-helix d) random-coil acidic domain
d) random-coil acidic domain
Gene knockdown via RNAi relies on the ability of eukaryotic cells to
degrade target mRNAs that are complementary to introduced dsRNA.
A cDNA library
doesn't contain introns because it is generated by copying messenger RNA (mRNA) with the enzyme reverse transcriptase and cloning the resulting complementary DNA (cDNA).
The action of a new drug is unknown, so you test various aspects of eukaryotic cell processes looking for an effect. You notice that the survival of cells exposed to this drug is very low. Further analysis shows that some proteins and mRNAs are much longer than they should be. One hypothesis is that the drug interferes with
either transcription termination signals or spliceosome activity.
The societal challenges created by next-generation sequencing are related to
ethical questions of confidentiality, estimation of disease risk for individuals, and reliable data storage and analysis.
An isolate of a mutant bacterium appears to grow more slowly than the wild-type population from which it was isolated. Further studies showed that the slower growth was due to a markedly reduced DNA polymerase I activity. From this information, one would expect that this organism would also be deficient in the activity of DNA
excision repair.
nonhomologous end joining is used to
fix double-strand DNA breaks.
What new technique or technology may revolutionize the way in which cell biologists alter the genomes of cells and organisms?
genome editing
The accompanying graph shows a growth curve of E. coli growing in a defined medium containing equal molar amounts of glucose and lactose. Based on your knowledge of the regulation of the lac operon, the best explanation of these results is that
glucose is used first. Once glucose becomes limiting, intracellular cAMP increases, forming cAMP-CAP complexes that activate the lac operon to use lactose.
Double-strand breaks can be repaired flawlessly by:
homologous recombination
Which of the following is a fundamental difference between gene regulation in bacteria compared to eukaryotes?
in eukaryotes, but not bacteria, transcription can be influenced by how effectively the DNA sequences of a promoter region interacts with histone octomers
An individual has been infected with a particular retrovirus. In order for the latent virus DNA to be inherited by subsequent generations stemming from this individual, it must be found
in germ line cells.
The energy for DNA polymerization is provided by the hydrolysis of
incoming nucleoside triphosphates (releasing PPi)
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 mostly likely explanation for this phenomenon? It is possible that the individuals with the cancer have:
inherited a mutation in a gene required for mismatch repair
You decide to use different bacterial strains (each having one protein of the replication machinery mutated) in order to examine the role of individual proteins in the normal process of DNA replication. 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?
initiation of DNA synthesis
Genes in eukaryotic cells often have intronic sequences coded for within DNA. These sequences are ultimately not translated into proteins. Why?
intronic sequences are removed from RNA molecules by a spliceosome, which works in the nucleus
In DNA replication, the leading strand of DNA _____, while the other newly forming strand, called the lagging strand, ________
is synthesized as a continuous chain; the new DNA is formed in a series of short, discontinuous fragments
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?
lagging-strand completion
Total nucleic acids are extracted from a culture of yeast cells and are then mixed with resin beads to which the polynucleotide 5-'TTTTTTTTTTTTTTTTT—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 the most abundant?
mRNA
It has been shown that inhibition of a key chromatin remodeling complex known as NuRD, by deleting one of its subunits, can result in a significant increase in the efficiency of reprogramming somatic cells... Such an observation suggests that the NuRD complex is normally involved in...
maintaining the epigenetic memory in somatic cells
In the absence of repair, replication of a double helix containing a mismatch would yield:
one DNA molecule with the normal sequence and one molecule with a mutated sequence
You have constructed a genomic library of Felis catus (domestic cat) in E. coli. You extract the plasmid DNA from the clones, digest the plasmid with restriction enzymes, separate the resulting fragments by gel electrophoresis, and transfer the fragments to a nylon membrane by the Southern blot procedure. You then use a fluorescently labeled probe that is complementary to a gene of interest that may be involved in feline lymphoma. The DNA corresponding to one clone yields a single fluorescent DNA band after probing the Southern blot. Based on this information
only the one clone described contains the part of the gene complementary to the probe on the fluorescent DNA band.
Which of the following enzymes is associated with the formation of peptide bonds?
peptidyl transferase
The error rate in the human genome is 3.4 bases per round of replication. All of the following contribute to reducing error except?
polyadenylation
Chloramphenicol blocks the peptidyl transferase reaction on ribosomes. Which of the following processes are inhibited?
protein elongation
Which of the following is not a structural motif found in a DNA-binding domain?
random-coil acidic domain
If you were designing a method to specifically inhibit prokaryotic transcription, but not eukaryotic transcription, interfering with which of the following would work best?
recognition of the prokaryotic promoter by RNA polymerase
Which of the following is not associated with mRNA processing in eukaryotes?
removal of exons
You are studying a eukaryotic gene whose initial transcript is 1500 nucleotides in length. The mature mRNA derived from the gene is 1200 nucleotides in length. What is the most probable reason for the discrepancy?
removal of introns
Alterations of histones by addition of methyl and acetyl groups to particular amino acids
results in the remodeling of chromatin that can activate or inhibit gene expression
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?
sliding clamp
To which part of an mRNA molecule do ribosomal subunits first bind?
the 5' end
Copying errors that slip by the replication machinery can be corrected by:
the DNA mismatch repair system
When a cell repairs a double-strand DNA break by the process of nonhomologous end joining:
the DNA sequence at the site of repair has been altered by a short deletion
The assembly of general transcription factors at a eukaryotic promoter typically begins at what site?
the TATA box
In the Sanger, or chain termination, method of DNA sequencing, incorporation of the nucleotides stops because
the dideoxynucleotide analogs have no 3ʹ-OH group to continue DNA synthesis.
RNA sequences, or RNA-Seq, can be used to track the expression of genes in different tissues. The technique counts the number of times a particular RNA sequence occurs in a given sample... The height of the lines indicates the number of sequencing reads and the structure of the mRNA is shown below, which the coding sequences indicated in light blue and the untranslated regions in purple. What could explain this pattern?
the mRNA is alternatively spliced in the liver compartment with the brain
The normal gene for hemoglobin was isolated, cloned in E. coli, and subjected to restriction enzyme digestion with BamHI. Following gel electrophoresis, three bands are routinely obtained. However, following the same procedure with the hemoglobin gene from an individual with sickle cell anemia, four bands are routinely obtained. These data suggest that
the mutation associated with sickle cell anemia results in the gain of a BamHI cut site
Mismatch repair targets improperly paired nucleotides. In prokaryotes, the incorrect member of an abnormal base pair can be differentiated from the correct member because
the original strand of DNA contains methylated bases while newly synthesized DNA does not; thus the correct member is in the methylated strand.
One of the societal benefits of genetic engineering today is
the production of human proteins by bacteria and yeast for the treatment of human diseases.
You have isolated a piece of DNA that you believe contains an interesting gene. Using a mix of RNA polymerase and ribonucleotides, you perform in vitro transcription. However, even though all of your controls work, no mRNA is created from your DNA fragment. Working backward, you note that your DNA preparation removed approximately 250 base pairs from the 5' end of the gene. The most likely explanation is that during DNA preparation
the promoter was removed.
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?
the transcription of a eukaryotic gene can be influenced by proteins that bind far from the promoter
The Trp operon in Escherichia coli encodes the components necessary for tryptophan biosynthesis. In the presence of the amino acid in a bacterium,
the tryptophan operator is bound to the tryptophan repressor.
Which of the following regions of the genomes is the least likely to be conserved over evolutionary time?
the upstream regulatory region of a gene that encodes the region conferring gene tissue specificity
In humans, xeroderma pigmentosum (XP) is a disorder of the nucleotide excision repair mechanism. These individuals are unable to repair DNA damage caused by ultraviolet light. Multiple basal cell carcinomas and other skin malignancies frequently occur at a young age in those with XP. Which of the following are the most prominent types of mutations in individuals suffering from XP?
thymine dimers
The mismatch repair system recognizes mismatched base pairs, removes a portion of the DNA strand containing error, and then resynthesizes the missing DNA using the correct sequence as template. But what if the mismatch system instead removed a piece of the DNA strand that contained the correct sequence? Replication of this improperly repaired sequence would produce:
two DNA molecules bearing the same mutation