Question 1

Which of the following best describes the semiconservative model of DNA replication, as supported by the Meselson-Stahl experiment?

Accepted Answer

Each daughter DNA molecule consists of one parental strand and one newly synthesized strand.

Question 2

During DNA replication, which enzyme is responsible for unwinding the double helix at the replication fork?

Accepted Answer

Helicase

Question 3

What is the primary function of single-strand binding proteins during DNA replication?

Accepted Answer

To stabilize unwound parental DNA strands and prevent them from re-pairing.

Question 4

Which enzyme relieves the strain caused by the unwinding of the DNA double helix ahead of the replication fork?

Accepted Answer

Topoisomerase

Question 5

Why is an RNA primer necessary for DNA polymerase to begin synthesis of a new DNA strand?

Accepted Answer

DNA polymerase can only add nucleotides to an existing 3' end.

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 it must work away from the replication fork in short segments.

Question 7

What are Okazaki fragments?

Accepted Answer

Short DNA segments synthesized on the lagging strand during DNA replication.

Question 8

Which enzyme replaces RNA primers with DNA nucleotides during DNA replication in E. coli?

Accepted Answer

DNA polymerase I

Question 9

What is the role of DNA ligase in DNA replication?

Accepted Answer

It joins the sugar-phosphate backbones of Okazaki fragments to form a continuous DNA strand.

Question 10

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

Accepted Answer

DNA polymerase adds nucleotides only to the 3' end of a growing DNA strand.

Question 11

A mutation in which enzyme would most likely result in increased sensitivity to UV light and a higher risk of skin cancer, as seen in xeroderma pigmentosum?

Accepted Answer

Nucleotide excision repair enzyme

Question 12

What is the evolutionary significance of rare mutations that escape DNA proofreading and repair?

Accepted Answer

They provide genetic variation that can be acted upon by natural selection.

Question 13

Why are telomeres important for eukaryotic chromosomes?

Accepted Answer

They protect genes near the ends of chromosomes from being eroded during successive rounds of DNA replication.

Question 14

Which enzyme is responsible for extending telomeres in eukaryotic germ cells?

Accepted Answer

Telomerase

Question 15

A scientist observes that after two rounds of DNA replication in a medium containing only $$^{14}N$$, the DNA extracted from E. coli consists of two bands: one at an intermediate density and one at a lighter density. Which model of DNA replication does this observation support?

Accepted Answer

Semiconservative model

Question 16

Which of the following best explains why DNA polymerase requires a primer to begin synthesis?

Accepted Answer

It can only add nucleotides to an existing 3' hydroxyl group.

Question 17

Which of the following is a direct result of the antiparallel structure of DNA during replication?

Accepted Answer

One strand is synthesized continuously, while the other is synthesized in fragments.

Question 18

Which of the following equations best represents the hydrolysis of pyrophosphate that drives DNA polymerization?

Accepted Answer

$$ \mathrm{PP_i \rightarrow 2P_i} $$

Question 19

A patient is found to have a defect in mismatch repair enzymes. Which of the following is a likely consequence?

Accepted Answer

Increased accumulation of mutations, leading to a higher risk of cancer.

DNA Replication and Repair: Mechanisms and Molecular Players

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