Molecular Cell Biology - Quiz 4
12. The difference between ATP and the nucleoside triphosphates used during DNA synthesis is that: A) the nucleoside triphosphates have the sugar deoxyribose; ATP has the sugar ribose. B) the nucleoside triphosphates have two phosphate groups; ATP has three phosphate groups. C) ATP contains three high-energy bonds; the nucleoside triphosphates have two. D) ATP is found only in human cells; the nucleoside triphosphates are found in all animal and plant cells. E) triphosphate monomers are active in the nucleoside triphosphates, but not in ATP.
A
18. In an experiment, DNA is allowed to replicate in an environment with all necessary enzymes, dATP, dCTP, dGTP, and radioactively labeled dTTP (3H thymidine) for several minutes and then switched to nonradioactive medium. It is then viewed by electron microscopy and autoradiography. The figure represents the results. Grains represent radioactive material within the replicating eye. Which of the following is the most likely interpretation? A) There are two replication forks going in opposite directions. B) Thymidine is only being added where the DNA strands are furthest apart. C) Thymidine is only added at the very beginning of replication. D) Replication proceeds in one direction only. E) Replication is not following base-pairing rules.
A
4. The leading and the lagging strands differ in that: A) the leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction. B) the leading strand is synthesized by adding nucleotides to the 3' end of the growing strand, and the lagging strand is synthesized by adding nucleotides to the 5' end. C) the lagging strand is synthesized continuously, whereas the leading strand is synthesized in short fragments that are ultimately stitched together. D) the leading strand is synthesized at twice the rate of the lagging strand.
A
9. What is the function of topoisomerase? A) Relieving strain in the DNA ahead of the replication fork B) Elongating new DNA at a replication fork by adding nucleotides to the existing chain C) Adding methyl groups to bases of DNA D) Unwinding of the double helix E) Stabilizing single-stranded DNA at the replication fork
A
11. A space probe returns with a culture of a microorganism found on a distant planet. Analysis shows that it is a carbon-based life-form that has DNA. You grow the cells in 15N medium for several generations and then transfer them to 14N medium. Which pattern in the figure would you expect after first round of replication if the DNA was replicated in a conservative manner? A-all 15 N DNA at bottom of tube B-half 15 N DNA at bottom of tube, half 14 N DNA at top of tube C-all 14 N DNA at top of tube D-all14 N 15 N hybrid in middle of tube E-half 14 N 15 N hybrid in middle of tube, half 14 N DNA at top of tube
B
13. What is meant by the description "antiparallel" regarding the strands that make up DNA? A) The twisting nature of DNA creates nonparallel strands. B) The 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand. C) Base pairings create unequal spacing between the two DNA strands. D) One strand is positively charged and the other is negatively charged. E) One strand contains only purines and the other contains only pyrimidines.
B
15. In E. coli, there is a mutation in a gene called dnaB that compromises the helicase activity. Which of the following would you expect as a result of this mutation? A) No proofreading will occur. B) No replication fork will be formed. C) DNA replication will not be affected at all. D) Replication will occur via RNA polymerase alone. E) Replication will require a DNA template from another source.
B
14. Which of the following statements about the structure or composition of DNA is FALSE? A) DNA is a double helix. B) Complementary base-pairing occurs between pyrimidine and purine bases. C) The amount of thymine closely approximates that of guanine within a particular organism. D) Each nucleotide within a DNA is separated by about 0.34 nm E) Adenine pairs with thymine and guanine with cytosine.
C
17. What is the role of DNA ligase during DNA replication? A) It synthesizes RNA nucleotides to make a primer. B) It catalyzes the lengthening of telomeres. C) It joins Okazaki fragments together. D) It unwinds the parental double helix. E) It stabilizes the unwound parental DNA.
C
19. Eukaryotic telomeres replicate differently than the rest of the chromosome. This is a consequence of which of the following? A) The evolution of telomerase enzyme B) DNA polymerase that cannot replicate the leading strand template to its 5' end C) Gaps left at the 5' end of the lagging strand D) Gaps left at the 3' end of the lagging strand because of the need for a primer E) The "no ends" of a circular chromosome
C
20. How can the leading and lagging strands be synthesized in a coordinated fashion? A) Specific enzymes control the size of the DNA opening. B) Lagging-strand binding proteins inhibit leading-strand replication if the strands become disproportionate in size. C) DNA Polymerase works as a dimer, and the looped lagging strand allows the enzyme to proceed in the same direction with each strand. D) All of the above. E) None of the above.
C
3. DNA is synthesized in which of the following directions? A) In the 5' > 3' direction on the leading strand and 3' > 5' direction in the lagging strand. B) The 3' > 5' direction on the leading strand and the 5' > 3' direction on the lagging strand. C) In the 5' > 3' direction on both DNA strands. D) The direction differs depending on the genes being duplicated. E) None of the above are correct.
C
7. In his work with pneumonia-causing bacteria and mice, Griffith found that: A) the protein coat from pathogenic cells was able to transform nonpathogenic cells. B) heat-killed pathogenic cells caused pneumonia. C) some substance from pathogenic cells was transferred to nonpathogenic cells, making them pathogenic. D) the polysaccharide coat of bacteria caused pneumonia. E) bacteriophages injected DNA into bacteria.
C
8. An Okazaki fragment has which of the following arrangements? A) primase, polymerase, ligase B) 3' RNA nucleotides, DNA nucleotides 5' C) 5' RNA nucleotides, DNA nucleotides 3' D) DNA polymerase I, DNA polymerase III E) 5' DNA to 3'
C
Compare and contrast B, A, and Z forms of DNA.
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DNA replication is always 5' to 3'. Explain what 5' to 3' means with respect to nucleotide subunits. Explain what activity of DNA polymerase necessitates that replication be 5' to 3' rather than 3' to 5'? What problems do you envision with 3' to 5' direction of DNA chain growth?
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Describe all the processes that contribute to the high fidelity of DNA replication.
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To incorporate radiolabeled nucleotides into newly synthesized DNA, researchers use α-phosphorus32-labeled nucleotides, in a DNA synthesis reaction, where the α denotes the position of the radioactive phosphate moiety. Explain why the α position--rather than the β or γ positions--is the best position for the radioactive group in these experiments.
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What is the difference between a nucleoside and a nucleotide? Why do you think it is important that the sugar phosphate backbone of DNA is held together by covalent bonds, and the cross-bridges between the two strands are held together by hydrogen bonds?
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Why is DNA synthesis discontinuous? Why is DNA ligase needed to join fragments of one strand of DNA?
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1. When a DNA molecule is described as replicating bidirectionally, that means that it has two: A) Chains. B) Independently replicating segment. C) Origins. D) Replication forks. E) Termination points.
D
5. After mixing a heat-killed, phosphorescent strain of bacteria with a living nonphosphorescent strain, you discover that some of the living cells are now phosphorescent. Which observations would provide the best evidence that the ability to fluoresce is a heritable trait? A) DNA passed from the heat-killed strain to the living strain. B) Protein passed from the heat-killed strain to the living strain. C) The phosphorescence in the living strain is especially bright. D) Descendants of the living cells are also phosphorescent. E) Both DNA and protein passed from the heat-killed strain to the living strain.
D
10. For a science fair project, two students decided to repeat the Hershey and Chase experiment, with modifications. They decided to label the nitrogen of the DNA, rather than the phosphate. They reasoned that each nucleotide has only one phosphate and two to five nitrogens. Thus, labeling the nitrogens would provide a stronger signal than labeling the phosphates. Why won't this experiment work? A) There is no radioactive isotope of nitrogen. B) Radioactive nitrogen has a half-life of 100,000 years, and the material would be too dangerous for too long. C) Avery et al. have already concluded that this experiment showed inconclusive results. D) Although there are more nitrogens in a nucleotide, labeled phosphates actually have 16 extra neutrons; therefore, they are more radioactive. E) Amino acids (and thus proteins) also have nitrogen atoms; thus, the radioactivity would not distinguish between DNA and proteins.
E
16. In the late 1950s, Meselson and Stahl grew bacteria in a medium containing "heavy" nitrogen (15N) and then transferred them to a medium containing 14N. Which of the results in the figure above would be expected after two rounds of DNA replication in the presence of 14N? A-all 15 N DNA at bottom of tube B-half 15 N DNA at bottom of tube, half 14 N DNA at top of tube C-all 14 N DNA at top of tube D-all14 N 15 N hybrid in middle of tube E-half 14 N 15 N hybrid in middle of tube, half 14 N DNA at top of tube
E
2. Suppose you are provided with an actively dividing culture of E. coli bacteria to which radioactive adenine has been added. What would happen if a cell replicates once in the presence of this radioactive base? A) One of the daughter cells, but not the other, would have radioactive DNA. B) Neither of the two daughter cells would be radioactive. C) All four bases of the DNA would be radioactive. D) Radioactive adenine would pair with nonradioactive guanine. E) DNA in both daughter cells would be radioactive.
E
6. At replication forks: A) DNA helicases make endonucleolytic cuts in DNA. B) DNA primers are degraded by ligase. C) DNA topoisomerases make endonucleolytic cuts in DNA. D) RNA primers are removed by primase. E) RNA primers are synthesized by primase.
E
