Question 1

Which enzyme is primarily responsible for unwinding the DNA double helix during the initial stage of DNA replication?

Accepted Answer

Helicase

Question 2

During DNA replication, what is the main function of primase?

Accepted Answer

It inserts an RNA primer to mark the starting point for DNA synthesis.

Question 3

Which of the following best describes the semi-conservative nature of DNA replication?

Accepted Answer

Each new DNA molecule contains one original strand and one newly synthesized strand.

Question 4

A scientist observes that after DNA replication, one strand of each DNA molecule is composed of nucleotides with radioactive labels present only in the original DNA. What does this observation support?

Accepted Answer

DNA replication is semi-conservative.

Question 5

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

Accepted Answer

Ligase

Question 6

Why are multiple replication bubbles formed during DNA replication in eukaryotic cells?

Accepted Answer

To speed up the replication process by allowing simultaneous replication at multiple sites.

Question 7

Which of the following correctly matches the enzyme with its function during DNA replication?

Accepted Answer

Ligase – connects Okazaki fragments

Question 8

A mutation occurs during DNA replication, resulting in a mismatched base pair. Which sequence of enzyme activities is most likely to repair this error?

Accepted Answer

READ enzyme, CUT enzyme, REPLACE enzyme

Question 9

If a cell is exposed to a chemical mutagen during the S-phase, which of the following is most likely to occur if the mutation is not repaired before mitosis?

Accepted Answer

The mutation may be passed on to both daughter cells.

Question 10

Which of the following best explains why the lagging strand is synthesized in short fragments during DNA replication?

Accepted Answer

DNA Polymerase can only add nucleotides in the 5' to 3' direction, but the lagging strand runs 3' to 5'.

Question 11

A patient is exposed to high levels of UV radiation, which causes thymine dimers in DNA. Which phase of the cell cycle is most critical for the repair of this damage before cell division?

Accepted Answer

G2 phase

Question 12

Which of the following base pairing rules is correct during DNA replication?

Accepted Answer

A pairs with T, C pairs with G

Question 13

If the DNA sequence on the template strand is 5'-ATCGGTA-3', what is the sequence of the newly synthesized complementary strand?

Accepted Answer

3'-TAGCCAT-5'

Question 14

Which of the following is NOT a possible consequence of an unrepaired mutation in DNA?

Accepted Answer

It could always result in cell death.

Question 15

A researcher inhibits the activity of DNA ligase in a cell. What is the most likely immediate effect on DNA replication?

Accepted Answer

Okazaki fragments on the lagging strand will remain unconnected.

Question 16

Which of the following best describes the role of single-stranded binding proteins during DNA replication?

Accepted Answer

They prevent the separated DNA strands from re-annealing.

Question 17

A cell completes DNA replication in approximately 7 hours. If the human genome contains about $$3 	imes 10^9$ base pairs, what is the average rate of DNA synthesis per second per cell? (Assume 7 hours = 25,200 seconds)

Accepted Answer

$$1.2 	imes 10^4$ base pairs/second

Question 18

Which of the following scenarios would most likely increase the mutation rate during DNA replication?

Accepted Answer

Exposure to pesticides

Question 19

If a mutation occurs in a gene that codes for a DNA repair enzyme, what is the most likely long-term consequence for the cell?

Accepted Answer

The cell may accumulate more mutations over time.

Question 20

Which of the following best explains why not all mutations are harmful?

Accepted Answer

Some mutations can lead to genetic diversity, which may be beneficial.

DNA Replication: Mechanisms and Repair

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