Question 1

Which enzyme is responsible for unwinding the DNA double helix at the replication fork, and what is the immediate result of its action?

Accepted Answer

Helicase; generates single-stranded DNA for template use

Question 2

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

Accepted Answer

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

Question 3

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

Accepted Answer

Failure to join Okazaki fragments on the lagging strand, resulting in fragmented DNA.

Question 4

Which of the following best explains why DNA polymerase requires an RNA primer to initiate DNA synthesis?

Accepted Answer

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

Question 5

A patient is exposed to ultraviolet (UV) radiation, which causes thymine dimers in their DNA. Which DNA repair mechanism is primarily responsible for correcting this type of damage?

Accepted Answer

Nucleotide excision repair (NER)

Question 6

Which of the following equations correctly represents the energy-releasing reaction that drives nucleotide addition during DNA replication?

Accepted Answer

$$\mathrm{dNTP} \rightarrow \mathrm{dNMP} + \mathrm{PP_i}$$

Question 7

If a eukaryotic cell's telomerase enzyme is nonfunctional, what is the most likely long-term consequence for the cell?

Accepted Answer

Progressive shortening of chromosome ends with each cell division, eventually leading to cell senescence.

Question 8

Which of the following best describes the proofreading function of DNA polymerase during replication?

Accepted Answer

The 3' to 5' exonuclease activity removes misincorporated nucleotides.

Question 9

A scientist observes that DNA replication in a mutant E. coli strain proceeds at only 100 nucleotides per second, compared to the wild-type rate of 500 nucleotides per second. Which enzyme is most likely defective in this mutant?

Accepted Answer

Helicase

Question 10

Which of the following statements about Okazaki fragments is correct?

Accepted Answer

They are short DNA segments synthesized on the lagging strand during replication.

Question 11

During DNA replication, which enzyme relieves supercoiling ahead of the replication fork?

Accepted Answer

Topoisomerase

Question 12

Which of the following best explains why the lagging strand requires more frequent primer synthesis than the leading strand?

Accepted Answer

The lagging strand is synthesized discontinuously, requiring a new primer for each Okazaki fragment.

Question 13

A defect in the 3' to 5' exonuclease activity of DNA polymerase would most likely result in which of the following?

Accepted Answer

Increased mutation rate due to loss of proofreading during DNA replication.

Question 14

Which of the following is the correct sequence of events for nucleotide excision repair (NER) of a thymine dimer?

Accepted Answer

Recognition, excision, DNA synthesis, ligation

Question 15

Which of the following best describes the role of telomerase in eukaryotic cells?

Accepted Answer

It extends the 3' end of the chromosome using an internal RNA template, preventing chromosome shortening.

Question 16

Which of the following is a direct result of the inability to remove RNA primers during DNA replication?

Accepted Answer

Short RNA segments remain embedded in the newly synthesized DNA.

Question 17

Which of the following best explains why DNA replication is highly accurate?

Accepted Answer

DNA polymerase has proofreading activity that removes misincorporated nucleotides.

Question 18

A researcher finds that a cell has a high frequency of single-stranded DNA breaks after replication. Which enzyme is most likely defective?

Accepted Answer

DNA ligase

Question 19

Which of the following best describes the direction in which DNA polymerase synthesizes new DNA?

Accepted Answer

5' to 3' direction

Question 20

Which of the following is a real-world consequence of defective mismatch repair during DNA replication?

Accepted Answer

Increased risk of hereditary cancers, such as Lynch syndrome

DNA Replication Essentials: Mechanisms, Enzymes, and Regulation

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