Question 1

Which model of DNA replication was supported by the Meselson-Stahl experiment, and what was the key evidence?

Accepted Answer

Semiconservative model; after two generations, DNA consisted of equal amounts of 'light' and 'half-heavy' DNA.

Question 2

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

Accepted Answer

To bind to DnaA boxes at the oriC and initiate strand separation.

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 bacterial DNA replication?

Accepted Answer

Because DNA polymerase III can only synthesize DNA in the 5’ to 3’ direction, resulting in discontinuous synthesis away from the replication fork.

Question 5

What is the role of DNA ligase in bacterial DNA replication?

Accepted Answer

It covalently links Okazaki fragments by forming ester bonds between DNA backbones.

Question 6

Which of the following best describes the directionality of DNA synthesis by DNA polymerases?

Accepted Answer

DNA polymerases synthesize DNA in the 5’ to 3’ direction only.

Question 7

What is the function of the β subunit of DNA polymerase III in E. coli?

Accepted Answer

It acts as a clamp protein, promoting the processivity of the enzyme.

Question 8

Which enzyme is responsible for removing RNA primers and replacing them with DNA during bacterial DNA replication?

Accepted Answer

DNA polymerase I

Question 9

What is the chemical reaction catalyzed by DNA polymerase during DNA synthesis?

Accepted Answer

Formation of a covalent (ester) bond between the 3’-OH of the previous deoxynucleotide and the innermost phosphate group of the incoming deoxyribonucleoside triphosphate, releasing pyrophosphate ($$PP_i).$$

Question 10

Which of the following mechanisms contributes to the high fidelity of DNA replication in E. coli?

Accepted Answer

The proofreading activity of DNA polymerase, which removes mismatched nucleotides using 3’ to 5’ exonuclease activity.

Question 11

A mutation in the gene encoding DNA adenine methyltransferase (Dam) would most likely affect which aspect of DNA replication?

Accepted Answer

The regulation of replication initiation due to improper methylation of GATC sites.

Question 12

What is the function of the protein Tus in bacterial DNA replication?

Accepted Answer

It binds to ter sequences and stops the movement of replication forks.

Question 13

Which of the following best explains why the lagging strand is synthesized discontinuously?

Accepted Answer

DNA polymerase can only add nucleotides to the 3’ end, and the lagging strand template is oriented in the 5’ to 3’ direction away from the fork.

Question 14

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

Accepted Answer

Catalyzing the formation of phosphodiester bonds between nucleotides.

Question 15

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

Accepted Answer

Replication forks will stall due to accumulation of positive supercoiling ahead of the fork.

Question 16

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

Accepted Answer

Initiation

Question 17

Which of the following best describes the composition of the DNA polymerase III holoenzyme in E. coli?

Accepted Answer

It consists of 10 different subunits, including the catalytic α subunit and the β clamp.

Question 18

What is the primary reason that DNA polymerase cannot initiate DNA synthesis de novo?

Accepted Answer

It requires a free 3’-OH group provided by an RNA primer.

Question 19

Which of the following best describes the fate of catenanes formed during bacterial DNA replication?

Accepted Answer

They are separated by the action of topoisomerase.

Bacterial DNA Replication: Mechanisms, Enzymes, and Experimental Evidence

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