Question 1

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

Accepted Answer

After one round of replication in $$^{14}N$$ medium, all DNA molecules had an intermediate density.

Question 2

What is the primary function of DNA helicase during chromosome replication?

Accepted Answer

To unwind the DNA double helix using the energy from ATP hydrolysis.

Question 3

Why is DNA replication described as 'bidirectional' in both circular bacterial and linear eukaryotic chromosomes?

Accepted Answer

Replication proceeds outward in both directions from each origin of replication.

Question 4

Which enzyme is responsible for removing RNA primers and filling in the resulting gaps with DNA during lagging strand synthesis?

Accepted Answer

DNA polymerase I

Question 5

What is the role of DNA topoisomerase during DNA replication?

Accepted Answer

To relieve supercoiling ahead of the replication fork by introducing transient nicks in the DNA.

Question 6

Which of the following best explains why DNA polymerase synthesizes DNA only in the 5' to 3' direction?

Accepted Answer

The 3' hydroxyl group is required for the addition of the next nucleotide, and proofreading can only occur in this direction.

Question 7

A mutation in the gene encoding single-strand binding protein (SSB) would most likely result in which of the following problems during DNA replication?

Accepted Answer

Single-stranded DNA would form secondary structures, impeding the progress of DNA polymerase.

Question 8

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

Accepted Answer

It extends the 3' end of linear chromosomes by adding repetitive DNA sequences.

Question 9

Which of the following is a direct consequence if the mismatch repair system (MutS/MutL) fails in a cell?

Accepted Answer

The mutation rate in the genome will increase, potentially leading to diseases such as cancer.

Question 10

In the context of the Okazaki experiment, what was the significance of the 'pulse-chase' labeling technique?

Accepted Answer

It demonstrated that short DNA fragments are precursors to longer DNA strands on the lagging strand.

Question 11

Which of the following equations best represents the energetics of nucleotide addition during DNA synthesis?

Accepted Answer

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

Question 12

A patient is found to have a genetic defect in their DNA ligase enzyme. Which of the following cellular processes would be most directly affected?

Accepted Answer

Joining of Okazaki fragments on the lagging strand during DNA replication.

Question 13

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

Accepted Answer

Their large size necessitates multiple starting points to ensure timely and complete replication.

Question 14

Which of the following scenarios would most likely result in a permanent mutation in the genome?

Accepted Answer

A mismatch escapes both proofreading by DNA polymerase and mismatch repair mechanisms.

Question 15

Which of the following is a key difference between DNA polymerase and RNA polymerase during nucleic acid synthesis?

Accepted Answer

DNA polymerase requires a pre-existing 3' hydroxyl group to initiate synthesis, while RNA polymerase can start de novo.

Question 16

A researcher exposes bacterial cells to UV light, resulting in the formation of thymine dimers. Which repair mechanism is most likely to be activated to correct this damage?

Accepted Answer

Nucleotide excision repair, involving nuclease, DNA polymerase, and DNA ligase.

Question 17

In a genetic complementation test using bacteriophage mutants, what does it indicate if two different mutants fail to complement each other?

Accepted Answer

The mutations are in the same gene.

Question 18

Which of the following best describes the function of Okazaki fragments during DNA replication?

Accepted Answer

They are short DNA fragments synthesized on the lagging strand and later joined to form a continuous strand.

Question 19

Which of the following best explains why the fidelity of DNA replication is so high?

Accepted Answer

It is due to the combined effects of base selection, proofreading by DNA polymerase, and mismatch repair.

Lecture 14 (Unit 2)-Chromosome Replication, Repair, and the Molecular Definition of the Gene

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