Question 1

Which of the following best describes the two-step process of DNA replication initiation in eukaryotes?

Accepted Answer

Licensing factors recruit inactive origins to form the pre-replication complex, and then initiating factors activate the replication machinery to convert the pre-RC to a pre-initiation complex.

Question 2

A temperature-sensitive mutant in a bacterial DNA polymerase shows normal growth at 30°C but fails to replicate DNA at 42°C. What is the most likely explanation for this phenotype?

Accepted Answer

The mutant protein is functional at the permissive temperature but loses function at the non-permissive temperature due to misfolding.

Question 3

Which of the following statements about DNA polymerase proofreading is correct?

Accepted Answer

Proofreading is performed by the 3' to 5' exonuclease activity, which removes incorrectly paired nucleotides.

Question 4

During DNA replication, which enzyme is responsible for synthesizing short RNA primers required for DNA polymerase to begin synthesis?

Accepted Answer

Primase

Question 5

What is the main function of the sliding clamp (e.g., the β-clamp in bacteria) during DNA replication?

Accepted Answer

It increases the processivity of DNA polymerase by preventing it from dissociating from the DNA template.

Question 6

Which of the following best explains why the lagging strand is synthesized discontinuously?

Accepted Answer

DNA polymerase can only synthesize DNA in the 5' to 3' direction, so the lagging strand is made in short fragments as the replication fork opens.

Question 7

A mutation in a gene encoding a licensing factor (such as Cdc6 or Cdt1) would most likely affect which stage of DNA replication?

Accepted Answer

Initiation (licensing)

Question 8

Which of the following equations correctly represents the formation of a phosphodiester bond during DNA synthesis?

Accepted Answer

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

Question 9

Why do eukaryotic chromosomes require telomeres?

Accepted Answer

To prevent the loss of genetic information due to the inability of DNA polymerase to fully replicate the ends of linear chromosomes.

Question 10

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

Accepted Answer

It extends the 3' end of the chromosome using an RNA template, allowing DNA polymerase to complete lagging strand synthesis.

Question 11

A mutation in a gene encoding a protein exclusively involved in the initiation of DNA replication would most likely result in which phenotype?

Accepted Answer

Cell growth stops immediately upon temperature shift to non-permissive conditions.

Question 12

Which of the following is a key difference between DNA polymerases involved in genome replication and those involved in DNA repair?

Accepted Answer

Genome-replicating polymerases have high processivity and proofreading activity, while repair polymerases are often error-prone and have lower processivity.

Question 13

Which of the following best explains why high-fidelity DNA polymerases have tightly fitted active sites?

Accepted Answer

To ensure only correct Watson-Crick base pairs fit, reducing the chance of misincorporation.

Question 14

In the context of Okazaki fragment processing, which enzyme is responsible for joining the fragments together?

Accepted Answer

DNA ligase

Question 15

A cell line is found to have abnormally short telomeres and undergoes premature senescence. Which enzyme is most likely defective in these cells?

Accepted Answer

Telomerase

Question 16

Which of the following best describes the function of single-strand binding proteins (SSBs) during DNA replication?

Accepted Answer

They stabilize single-stranded DNA and prevent it from re-annealing during replication.

Question 17

Which of the following is a consequence of the end-replication problem in linear chromosomes?

Accepted Answer

Progressive shortening of chromosomes with each cell division.

Question 18

Which of the following best explains the role of DDK (Dbf4-dependent kinase) in eukaryotic DNA replication?

Accepted Answer

It activates the MCM helicase, converting the pre-replication complex to a pre-initiation complex.

DNA Replication II: Initiation, Licensing, and Mutant Analysis in Eukaryotes and Bacteria

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