Question 1

Which experimental result provided the strongest evidence for the semiconservative model of DNA replication?

Accepted Answer

The appearance of DNA with intermediate density after one generation in light medium

Question 2

What is the primary function of the DnaA protein during the initiation of DNA replication in E. coli?

Accepted Answer

Binds to the 9-mer repeats at oriC to initiate strand separation

Question 3

Which enzyme is responsible for relieving positive supercoiling ahead of the replication fork in E. coli?

Accepted Answer

Topoisomerase (DNA gyrase)

Question 4

Why does DNA polymerase synthesize DNA only in the 5′→3′ direction?

Accepted Answer

It can only add nucleotides to a free 3′-hydroxyl group

Question 5

Which of the following best describes the role of the sliding clamp in DNA replication?

Accepted Answer

It holds DNA polymerase III on the DNA, increasing processivity

Question 6

During lagging strand synthesis, what is the correct sequence of events for Okazaki fragment maturation?

Accepted Answer

Primase synthesizes primer → DNA polymerase III extends fragment → RNase H and DNA polymerase I remove and replace primer → DNA ligase seals nicks

Question 7

What is the function of single-strand binding proteins (SSBs) during DNA replication?

Accepted Answer

They stabilize single-stranded DNA and prevent reannealing

Question 8

Which of the following statements about the trombone-loop model of DNA replication is correct?

Accepted Answer

It explains how both DNA polymerases move together at the fork, allowing lagging strand looping

Question 9

A mutation in the gene encoding DNA ligase would most directly result in which of the following defects during DNA replication?

Accepted Answer

Accumulation of nicks between Okazaki fragments on the lagging strand

Question 10

In the Meselson-Stahl experiment, what would be the expected result after two generations if DNA replication were dispersive?

Accepted Answer

One band at intermediate density

Question 11

Which enzyme is responsible for synthesizing short RNA primers during DNA replication in E. coli?

Accepted Answer

Primase

Question 12

What is the role of the clamp loader (γ complex) in the DNA polymerase III holoenzyme?

Accepted Answer

It loads sliding clamps onto the primer:template junction

Question 13

Which of the following best explains why the origin of replication (oriC) in E. coli is A–T rich?

Accepted Answer

A–T base pairs are easier to separate due to fewer hydrogen bonds

Question 14

A researcher observes that after DNA replication in E. coli, the resulting DNA molecules each contain one old and one new strand. This observation supports which model of replication?

Accepted Answer

Semiconservative

Question 15

Which of the following is TRUE regarding Okazaki fragments?

Accepted Answer

They are short DNA fragments synthesized on the lagging strand

Question 16

Which enzyme removes RNA primers and fills in the resulting gaps with DNA during lagging strand synthesis in E. coli?

Accepted Answer

DNA polymerase I

Question 17

If a mutation prevents the function of DnaC in E. coli, which step of DNA replication would be directly affected?

Accepted Answer

Loading of DNA helicase onto the DNA

Question 18

Which of the following best describes the directionality of DNA synthesis at the replication fork?

Accepted Answer

Both leading and lagging strands are synthesized 5′→3′

Question 19

A patient is treated with a drug that inhibits bacterial DNA gyrase. What is the most likely effect on E. coli DNA replication?

Accepted Answer

Supercoiling ahead of the replication fork is not relieved, stalling replication

Question 20

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

Accepted Answer

One strand is synthesized continuously, the other discontinuously

DNA Replication in Prokaryotes: Mechanisms and Enzymology (E. coli Model)

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