Question 1

Which experimental result provided the strongest evidence that DNA replication in E. coli is semiconservative rather than conservative or dispersive?

Accepted Answer

The presence of a single intermediate-density band after one generation and both intermediate and light bands after two generations, as shown in the Meselson–Stahl experiment.

Question 2

During DNA replication in E. coli, which enzyme is primarily responsible for synthesizing the majority of the new DNA strand, and what is its directionality?

Accepted Answer

DNA polymerase III; $$5' \rightarrow 3'$$

Question 3

A mutation in the gene encoding DNA ligase in E. coli would most likely result in which of the following phenotypes?

Accepted Answer

Accumulation of Okazaki fragments on the lagging strand due to inability to seal nicks between fragments.

Question 4

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

Accepted Answer

Eukaryotic chromosomes are linear and much larger, so multiple origins allow rapid and complete replication.

Question 5

What is the primary function of the sliding DNA clamp in the DNA polymerase III holoenzyme complex?

Accepted Answer

To increase the processivity of DNA polymerase by preventing its dissociation from the template strand.

Question 6

A patient is found to have a genetic disorder characterized by rapid telomere shortening and premature cellular senescence. Which enzyme is most likely deficient in this patient?

Accepted Answer

Telomerase

Question 7

Which of the following statements about Okazaki fragments is correct?

Accepted Answer

They are short DNA fragments synthesized discontinuously on the lagging strand, each initiated by an RNA primer.

Question 8

In the context of DNA replication, what is the role of DNA gyrase?

Accepted Answer

It relieves supercoiling tension ahead of the replication fork by making transient cuts in the DNA.

Question 9

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

Accepted Answer

They bind to and stabilize single-stranded DNA to prevent re-annealing during replication.

Question 10

A temperature-sensitive mutation in the gene encoding DNA helicase in E. coli would most likely result in which of the following outcomes at the restrictive temperature?

Accepted Answer

Inability to unwind the DNA double helix, halting replication fork progression.

Question 11

Which of the following equations correctly represents the directionality of DNA synthesis by DNA polymerases?

Accepted Answer

$$5' \rightarrow 3'$$

Question 12

In eukaryotic DNA replication, what is the primary role of chromatin assembly factors (CAFs)?

Accepted Answer

To assemble nucleosomes onto newly synthesized DNA strands.

Question 13

A researcher is studying a mutant yeast strain that lacks autonomously replicating sequences (ARSs). What is the most likely consequence for DNA replication in this strain?

Accepted Answer

Replication will initiate at random locations, leading to incomplete or inefficient DNA synthesis.

Question 14

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

Accepted Answer

DNA polymerase can only add nucleotides to a free $$3'-OH $$group, which is provided by the primer.

Question 15

A cell line is found to have a proofreading-deficient DNA polymerase. What is the most likely consequence for the cell?

Accepted Answer

Increased frequency of mutations due to inability to remove misincorporated nucleotides.

Question 16

Which of the following is a key difference between DNA replication in prokaryotes and eukaryotes?

Accepted Answer

Eukaryotes have multiple origins of replication per chromosome, while prokaryotes typically have a single origin.

Question 17

A scientist observes that after two rounds of DNA replication in the presence of labeled nucleotides, only one chromatid of each chromosome is labeled in a eukaryotic cell. Which experiment does this observation most closely resemble?

Accepted Answer

The Taylor–Woods–Hughes experiment in Vicia faba root tips.

Question 18

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

Accepted Answer

It adds repetitive DNA sequences to the ends of chromosomes to prevent loss of genetic information.

Question 19

Which of the following is a real-world consequence of loss of telomerase activity in human somatic cells?

Accepted Answer

Progressive shortening of telomeres, leading to cellular senescence and aging.

Question 20

A patient with a rare genetic disorder is found to have a mutation in the gene encoding the catalytic subunit of telomerase (TERT). Which of the following is the most likely molecular consequence?

Accepted Answer

Failure to extend the G-rich strand at chromosome ends, resulting in telomere shortening.

DNA Replication: Mechanisms and Regulation

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