Question 1

Which model of DNA replication was confirmed by the Meselson–Stahl experiment in E. coli, and what was the key evidence supporting this model?

Accepted Answer

Semiconservative replication; the experiment showed one hybrid band after one round and both hybrid and light bands after two rounds.

Question 2

During DNA replication, which enzyme is responsible for relieving the tension caused by supercoiling ahead of the replication fork?

Accepted Answer

DNA gyrase

Question 3

If DNA replication were conservative, what would be the expected result after two rounds of replication in the Meselson–Stahl experiment?

Accepted Answer

One old, heavy band and one new, light band

Question 4

Which equation best represents the chemical reaction catalyzed by DNA polymerase during chain elongation?

Accepted Answer

$$(dNMP)_n + dNTP \rightarrow (dNMP)_{n+1} + PP_i$$

Question 5

Which DNA polymerase is primarily responsible for the synthesis of new DNA during replication in E. coli?

Accepted Answer

DNA polymerase III

Question 6

What is the function of primase during DNA replication?

Accepted Answer

Synthesizes RNA primers to provide a free 3' OH group for DNA polymerase

Question 7

Which direction does DNA polymerase synthesize new DNA?

Accepted Answer

5' to 3'

Question 8

What is the role of single-stranded binding proteins (SSBPs) during DNA replication?

Accepted Answer

They bind to single-stranded DNA to prevent re-annealing and protect it from nucleases.

Question 9

Which enzyme is responsible for joining Okazaki fragments on the lagging strand during DNA replication?

Accepted Answer

DNA ligase

Question 10

A mutation in the gene encoding DNA ligase would most likely result in which phenotype during DNA replication?

Accepted Answer

Accumulation of unjoined Okazaki fragments

Question 11

Which property is shared by all known bacterial DNA polymerases?

Accepted Answer

5' to 3' polymerization activity

Question 12

What is the primary function of DNA polymerase I during DNA replication in E. coli?

Accepted Answer

Removes RNA primers and fills in gaps with DNA

Question 13

Which of the following best describes the difference between the leading and lagging strands during DNA replication?

Accepted Answer

The leading strand is synthesized continuously, while the lagging strand is synthesized discontinuously as Okazaki fragments.

Question 14

Which protein initiates the unwinding of the DNA helix at the origin of replication in E. coli?

Accepted Answer

DnaA

Question 15

A temperature-sensitive mutation in a gene encoding a replication enzyme is an example of which type of mutation?

Accepted Answer

Conditional mutation

Question 16

Which equation represents the directionality of DNA synthesis?

Accepted Answer

$$5' \rightarrow 3'$$

Question 17

Which enzyme is recruited to the replication fork by helicase to synthesize the RNA primer?

Accepted Answer

Primase

Question 18

What is the role of DNA polymerase III core enzymes at the replication fork?

Accepted Answer

They synthesize both the leading and lagging strands.

Question 19

Which of the following is NOT a function of DNA polymerase III in E. coli?

Accepted Answer

Initiating DNA synthesis de novo

Question 20

Why are Okazaki fragments formed during DNA replication?

Accepted Answer

Because the lagging strand template is oriented opposite to the direction of DNA synthesis

Ch 10 P1 DNA Replication: Mechanisms and Enzymology

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