Question 1

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

Accepted Answer

After two generations, DNA consisted of equal amounts of 'light' and 'half-heavy' DNA, which is only consistent with the semiconservative model.

Question 2

What is the primary function of the DnaA protein during the initiation of bacterial DNA replication?

Accepted Answer

It binds to DnaA boxes at oriC, facilitating the unwinding of DNA at AT-rich regions.

Question 3

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

Accepted Answer

Topoisomerase II (DNA gyrase)

Question 4

Why are multiple RNA primers required on the lagging strand during DNA replication?

Accepted Answer

Because the lagging strand is synthesized discontinuously as Okazaki fragments, each requiring a primer.

Question 5

Which of the following best describes the role of DNA polymerase I in prokaryotic DNA replication?

Accepted Answer

It removes RNA primers and fills the gaps with DNA.

Question 6

What is the function of the β subunit of DNA polymerase III holoenzyme?

Accepted Answer

It forms a sliding clamp around DNA, increasing the processivity of the enzyme.

Question 7

Which of the following equations correctly represents the chemical reaction catalyzed by DNA polymerase during DNA synthesis?

Accepted Answer

$$\mathrm{dNTP} + (DNA)_{n} \rightarrow (DNA)_{n+1} + 2\,\mathrm{PP_i}$$

Question 8

A mutation in the gene encoding DNA ligase would most directly affect which step of DNA replication?

Accepted Answer

Joining of Okazaki fragments on the lagging strand

Question 9

Which feature of DNA polymerase III contributes most to its high fidelity during DNA replication?

Accepted Answer

Its 3’ to 5’ exonuclease proofreading activity

Question 10

In E. coli, what is the significance of GATC methylation sites at the origin of replication (oriC)?

Accepted Answer

They regulate the timing of DNA replication initiation by distinguishing parental from daughter strands.

Question 11

Which protein binds to ter sequences to halt the progression of the replication fork in E. coli?

Accepted Answer

Tus

Question 12

A bacterial cell is exposed to a chemical that inhibits topoisomerase II. What is the most likely consequence during DNA replication?

Accepted Answer

Positive supercoiling will accumulate ahead of the replication fork, stalling replication.

Question 13

Which of the following best explains why DNA synthesis is continuous on the leading strand but discontinuous on the lagging strand?

Accepted Answer

DNA polymerase can only synthesize DNA in the 5’ to 3’ direction, and the two template strands are antiparallel.

Question 14

Which of the following is NOT a function of single-stranded binding proteins during DNA replication?

Accepted Answer

Synthesizing RNA primers

Question 15

A mutation in the gene encoding primase would most directly affect which aspect of DNA replication?

Accepted Answer

The synthesis of short RNA primers required for DNA polymerase to initiate synthesis

Question 16

Which of the following statements about Okazaki fragments is TRUE?

Accepted Answer

They are joined together by DNA ligase after RNA primers are replaced with DNA.

Question 17

Which step in DNA replication is most directly regulated by the methylation state of GATC sites at oriC?

Accepted Answer

Initiation

Question 18

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

Accepted Answer

It loads the β clamp onto DNA, allowing DNA polymerase III to remain attached to the template.

Question 19

What is the primary reason that DNA replication in bacteria is highly accurate?

Accepted Answer

The proofreading activity of DNA polymerases and the stability of proper base pairing

Question 20

Which of the following best explains why catenanes form during bacterial DNA replication and how they are resolved?

Accepted Answer

Catenanes are intertwined daughter DNA molecules formed after replication and are separated by topoisomerase.

Prokaryotic DNA Replication: Mechanisms, Models, and Key Proteins

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