Q: A student is analyzing a DNA molecule after replication and finds that each daughter strand contains 50% original DNA and 50% new DNA. Which equation best represents the composition of each daughter strand?

$$\text{Daughter Strand} = 0.5 \times \text{Original DNA} + 0.5 \times \text{New DNA}$$

Question 1

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

Accepted Answer

Helicase

Question 2

During DNA replication, what is the function of single-stranded binding proteins?

Accepted Answer

They prevent the separated DNA strands from re-forming the double helix.

Question 3

DNA replication is described as 'semi-conservative.' What does this mean?

Accepted Answer

Each new DNA molecule contains half of the original DNA and half new nucleotides.

Question 4

Which strand of DNA is replicated continuously during DNA replication?

Accepted Answer

Leading strand (3’)

Question 5

What is the role of DNA ligase during DNA replication?

Accepted Answer

It repairs the sugar-phosphate backbone and connects Okazaki fragments.

Question 6

A mutation occurs during DNA replication. Which sequence of enzyme actions is most likely to repair this mutation?

Accepted Answer

READ enzymes → CUT enzymes → REPLACE enzymes

Question 7

If a cell fails to repair a mutation during the G2 phase, which of the following outcomes is LEAST likely?

Accepted Answer

The cell will always die immediately.

Question 8

Which of the following best describes the directionality of DNA polymerase activity on the leading and lagging strands?

Accepted Answer

DNA polymerase synthesizes both strands in the 5’ to 3’ direction.

Question 9

Which of the following is a plausible consequence of exposure to physical substances such as radiation during DNA replication?

Accepted Answer

Formation of mutations in the DNA sequence.

Question 10

During DNA replication, which enzyme is responsible for inserting an RNA primer to mark the starting point for nucleotide addition?

Accepted Answer

Primase

Question 11

A student is analyzing a DNA molecule after replication and finds that each daughter strand contains 50% original DNA and 50% new DNA. Which equation best represents the composition of each daughter strand?

Accepted Answer

$$	ext{Daughter Strand} = 0.5 	imes 	ext{Original DNA} + 0.5 	imes 	ext{New DNA}$$

Question 12

Which of the following best explains why multiple replication bubbles form during DNA replication?

Accepted Answer

To allow DNA replication to occur faster by replicating at multiple sites simultaneously.

Question 13

A patient is exposed to a chemical mutagen. Which step in the DNA repair process is most likely to be impaired if the 'CUT' enzymes are nonfunctional?

Accepted Answer

Removal of mismatched base pairs

Question 14

Which of the following base pairings is correct according to the rules of DNA replication?

Accepted Answer

T pairs with A

Question 15

If the replication of DNA takes 7–8 hours to complete, approximately how many base pairs are replicated per hour, given that the human genome contains 3 billion base pairs?

Accepted Answer

$$\frac{3 	imes 10^9$}{7} \approx 4.29 	imes 10^8$ base pairs per hour

Question 16

Which of the following scenarios best illustrates the importance of DNA repair enzymes in preventing disease?

Accepted Answer

A cell with a mutation in a tumor suppressor gene fails to repair the error, leading to uncontrolled cell division.

Question 17

Which enzyme is responsible for facilitating the bonding of new complementary nucleotides to the template DNA strand during replication?

Accepted Answer

DNA Polymerase

Question 18

A scientist observes that the lagging strand is synthesized in short fragments during DNA replication. What are these fragments called?

Accepted Answer

Okazaki fragments

Question 19

Which phase of the cell cycle is DNA replication completed, and mutation checking occurs?

Accepted Answer

S-phase for replication; G2 phase for mutation checking

DNA Replication and Repair: Structure, Process, and Significance

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