Question 1

Which experimental result from the Meselson-Stahl experiment provided the strongest evidence for the semiconservative model of DNA replication?

Accepted Answer

After two generations in 14N, DNA consisted of equal amounts of light and half-heavy DNA.

Question 2

A mutation in E. coli prevents the methylation of GATC sites at oriC. What is the most likely consequence for DNA replication?

Accepted Answer

Replication will not initiate efficiently, as the cell cannot distinguish newly replicated DNA from old DNA.

Question 3

Which of the following best describes the role of DNA polymerase I during bacterial DNA replication?

Accepted Answer

It removes RNA primers and fills in the resulting gaps with DNA.

Question 4

A researcher observes that Okazaki fragments are not being joined together on the lagging strand in a mutant E. coli strain. Which enzyme is most likely defective?

Accepted Answer

DNA ligase

Question 5

Which of the following equations correctly represents the chemical reaction catalyzed by DNA polymerase during DNA synthesis?

Accepted Answer

$$\mathrm{(dNMP)_{n}} + \mathrm{dNTP} \rightarrow \mathrm{(dNMP)_{n+1}} + \mathrm{PP_i}$$

Question 6

In eukaryotic DNA replication, which enzyme is responsible for removing RNA primers from Okazaki fragments?

Accepted Answer

Flap endonuclease

Question 7

A patient’s cancer cells are found to have abnormally high telomerase activity. What is the most likely effect of this on the cancer cells?

Accepted Answer

Maintenance of telomere length, allowing unlimited cell division.

Question 8

Which of the following statements about the directionality of DNA synthesis is correct?

Accepted Answer

DNA polymerases synthesize DNA in the 5-prime to 3-prime direction only.

Question 9

A mutation in the beta subunit of DNA polymerase III in E. coli would most likely result in which of the following?

Accepted Answer

Decreased processivity of DNA synthesis, leading to frequent dissociation from the template.

Question 10

Which feature of eukaryotic origins of replication distinguishes them from bacterial origins?

Accepted Answer

They are often associated with nucleosome-free regions and G-quadruplex motifs.

Question 11

During DNA replication, which protein is responsible for relieving positive supercoiling ahead of the replication fork in bacteria?

Accepted Answer

Topoisomerase II (DNA gyrase)

Question 12

A mutation eliminates the 3-prime to 5-prime exonuclease activity of DNA polymerase III. What is the most likely consequence?

Accepted Answer

Increased frequency of replication errors due to loss of proofreading.

Question 13

Which of the following best explains why eukaryotic chromosomes require multiple origins of replication?

Accepted Answer

Eukaryotic chromosomes are long and linear, so multiple origins ensure timely replication.

Question 14

Which of the following is a direct result of the inability of DNA polymerase to initiate synthesis without a primer at the ends of linear chromosomes?

Accepted Answer

Progressive shortening of chromosomes with each cell division.

Question 15

Which of the following accurately describes the function of the primosome during bacterial DNA replication?

Accepted Answer

It unwinds the DNA double helix and synthesizes RNA primers.

Question 16

A scientist is studying a eukaryotic cell line with a mutation that prevents the formation of the pre-replication complex (preRC). Which process will be directly affected?

Accepted Answer

Initiation of DNA replication at origins.

Question 17

Which of the following best describes the role of telomerase in eukaryotic cells?

Accepted Answer

It extends the 3-prime overhang of telomeres using an RNA template.

Question 18

Which DNA polymerase is primarily responsible for processive elongation of the leading strand during eukaryotic DNA replication?

Accepted Answer

DNA polymerase epsilon

Question 19

A bacterial cell is treated with a drug that inhibits topoisomerase II. What is the most likely effect on DNA replication?

Accepted Answer

Replication forks will stall due to accumulation of positive supercoils ahead of the fork.

Question 20

Which of the following is a key difference between the removal of RNA primers in prokaryotic and eukaryotic DNA replication?

Accepted Answer

Prokaryotes use DNA polymerase I, while eukaryotes use flap endonuclease.

DNA Replication: Mechanisms, Enzymes, and Regulation (Chapter 11 Study Notes)

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