Question 1

Which enzyme is responsible for relieving the strain ahead of the replication fork during DNA replication by breaking, swiveling, and rejoining DNA strands?

Accepted Answer

Topoisomerase

Question 2

During DNA replication, which of the following statements about the directionality of DNA synthesis is correct?

Accepted Answer

DNA polymerases can add nucleotides only to the free 3′ end of a growing strand.

Question 3

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

Accepted Answer

They stabilize unwound parental DNA strands.

Question 4

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

Accepted Answer

The leading strand is synthesized in the same direction as the movement of the replication fork, whereas the lagging strand is synthesized in the opposite direction.

Question 5

Which enzyme is responsible for synthesizing short RNA primers during DNA replication?

Accepted Answer

Primase

Question 6

What provides the energy for the addition of a nucleotide to a growing DNA strand during replication?

Accepted Answer

The hydrolysis of the last two phosphate groups from a nucleoside triphosphate, forming pyrophosphate ($$PP_i$$), which is then hydrolyzed to two inorganic phosphates ($$2P_i).$$

Question 7

In E. coli, which enzyme is primarily responsible for replacing RNA primers with DNA nucleotides?

Accepted Answer

DNA polymerase I

Question 8

Which of the following statements about Okazaki fragments is true?

Accepted Answer

They are short DNA fragments synthesized on the lagging strand.

Question 9

A mutation in the gene encoding DNA ligase would most directly affect which process during DNA replication?

Accepted Answer

Joining Okazaki fragments on the lagging strand.

Question 10

Which of the following is NOT a requirement for DNA polymerase to synthesize a new DNA strand?

Accepted Answer

A free 5′ phosphate group on the template strand.

Question 11

If a bacterial cell has a mutation that inactivates primase, what would be the most immediate effect on DNA replication?

Accepted Answer

No RNA primers would be synthesized, so DNA polymerase could not initiate DNA synthesis.

Question 12

Which of the following best explains why DNA synthesis is more complex on the lagging strand than on the leading strand?

Accepted Answer

The lagging strand template runs in the 5′ → 3′ direction into the replication fork, requiring discontinuous synthesis away from the fork.

Question 13

Which of the following is the correct complementary DNA strand for 5′-AACGGTCCAGTCCAAGTTACG-3′?

Accepted Answer

3′-TTGCCAGGTCAGGTTCAATGC-5′

Question 14

Which of the following best describes the antiparallel nature of DNA?

Accepted Answer

One DNA strand runs 5′ → 3′, while the other runs 3′ → 5′.

Question 15

A researcher is studying a eukaryotic chromosome and observes hundreds of replication bubbles forming simultaneously. What is the most likely explanation for this observation?

Accepted Answer

Eukaryotic chromosomes have multiple origins of replication to ensure rapid and complete DNA replication.

Question 16

Which of the following is a direct consequence if DNA polymerase III is nonfunctional in a bacterial cell?

Accepted Answer

The cell cannot synthesize new DNA strands on either the leading or lagging strand.

Question 17

During DNA replication, which enzyme is responsible for unwinding the parental double helix at the replication fork?

Accepted Answer

Helicase

Question 18

Which of the following best explains why DNA replication is considered semiconservative?

Accepted Answer

Each daughter DNA molecule consists of one parental strand and one newly synthesized strand.

Question 19

A mutation in the gene encoding single-strand binding proteins would most likely result in which of the following?

Accepted Answer

The unwound DNA strands would re-anneal before replication could proceed.

Question 20

Which of the following is true regarding the rate of DNA replication in bacteria compared to human cells?

Accepted Answer

Bacteria replicate DNA at a rate of about 500 nucleotides per second, while human cells replicate at about 50 nucleotides per second.

DNA Replication: Mechanisms and Key Enzymes part 2

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