Question 1

Which enzyme is responsible for unwinding the DNA double helix at the replication fork, and what is the energy source for this process?

Accepted Answer

Helicase; energy from ATP hydrolysis ($$\mathrm{ATP} \rightarrow \mathrm{ADP} + \mathrm{P_i})$$

Question 2

During DNA replication, which of the following statements best describes the difference between the leading and lagging strands?

Accepted Answer

The leading strand is synthesized continuously in the 5' to 3' direction, while the lagging strand is synthesized discontinuously as Okazaki fragments.

Question 3

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

Accepted Answer

They stabilize unwound DNA strands and prevent them from re-annealing.

Question 4

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

Accepted Answer

DNA polymerase III can only add nucleotides to a free 3'-OH group provided by the RNA primer.

Question 5

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

Accepted Answer

Synthesis of RNA primers on both the leading and lagging strands.

Question 6

In the context of DNA supercoiling, what is the effect of DNA gyrase (a type II topoisomerase) on bacterial DNA?

Accepted Answer

It introduces negative supercoils by making double-stranded breaks.

Question 7

Which of the following best describes the central dogma of molecular biology as depicted in the provided diagram?

Accepted Answer

DNA is transcribed into RNA, which is then translated into protein.

Question 8

If a bacterial cell is treated with a drug that inhibits the activity of topoisomerase, what is the most likely consequence during DNA replication?

Accepted Answer

Replication will stall due to increased torsional strain ahead of the replication fork.

Question 9

Which of the following sequences correctly represents the order of events during bacterial chromosomal DNA replication?

Accepted Answer

DnaA binds origin → Helicase unwinds DNA → Primase synthesizes RNA primer → DNA polymerase III extends DNA

Question 10

A researcher observes that after DNA replication, the newly synthesized DNA is not properly packaged and remains relaxed rather than supercoiled. Which enzyme is most likely defective?

Accepted Answer

DNA gyrase (topoisomerase II)

Question 11

Which of the following best explains why Okazaki fragments are formed during DNA replication?

Accepted Answer

DNA polymerase III can only synthesize DNA in the 5' to 3' direction, requiring discontinuous synthesis on the lagging strand.

Question 12

During DNA replication, which of the following is the correct function of the Tus protein in E. coli?

Accepted Answer

It binds to the terminus of replication and halts the progression of the replication fork.

Question 13

A patient is exposed to a novel antibiotic that specifically inhibits DnaA protein function. Which of the following processes will be directly affected?

Accepted Answer

Initiation of chromosomal DNA replication

Question 14

Which of the following best describes the role of primase during DNA replication?

Accepted Answer

It synthesizes short RNA primers to provide a 3'-OH group for DNA polymerase.

Question 15

If the DNA helix is underwound to less than 10.5 base pairs per turn, what is the resulting effect on DNA structure?

Accepted Answer

Negative supercoiling occurs, making the DNA more compact.

Question 16

A mutation prevents the formation of RNA primers during DNA replication. Which enzyme is most likely nonfunctional?

Accepted Answer

DnaG primase

Question 17

Which of the following is a direct consequence if DNA polymerase III lacked 3'-OH requirement for nucleotide addition?

Accepted Answer

It could initiate DNA synthesis de novo, without a primer.

Molecular Information Flow and DNA Replication in Microbiology

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