Question 1

Which experimental result from the Meselson–Stahl experiment provided the strongest evidence for the semiconservative model of DNA replication?

Accepted Answer

After one generation, all DNA molecules had intermediate density, and after two generations, both light and intermediate DNA were present.

Question 2

DNA polymerase can only add nucleotides to which end of a growing DNA strand?

Accepted Answer

The 3' end

Question 3

Why is DNA polymerization considered an exergonic reaction?

Accepted Answer

Because the hydrolysis of dNTPs' phosphate groups provides enough energy to drive the reaction.

Question 4

Which enzyme is responsible for relieving the tension created ahead of the replication fork during DNA unwinding?

Accepted Answer

Topoisomerase

Question 5

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

Accepted Answer

To prevent separated DNA strands from re-annealing

Question 6

Which of the following best describes the synthesis of the lagging strand during DNA replication?

Accepted Answer

It is synthesized discontinuously away from the replication fork in short fragments.

Question 7

What is the role of DNA ligase in DNA replication?

Accepted Answer

It joins Okazaki fragments by forming phosphodiester bonds.

Question 8

Why do eukaryotic chromosomes have multiple origins of replication?

Accepted Answer

Because their chromosomes are much larger and linear, requiring multiple replication bubbles to speed up DNA synthesis.

Question 9

What problem arises during the replication of the ends of linear chromosomes, and how is it solved?

Accepted Answer

The lagging strand cannot be completed; telomerase extends the 3' end using its own RNA template.

Question 10

Which of the following statements about telomerase is TRUE?

Accepted Answer

Telomerase uses an RNA template to extend the 3' end of the lagging strand.

Question 11

A mutation disables the proofreading function of DNA polymerase. What is the most likely consequence?

Accepted Answer

The frequency of mutations during DNA replication will increase.

Question 12

Which repair mechanism is responsible for correcting mismatched bases that escape proofreading during DNA replication?

Accepted Answer

Mismatch repair

Question 13

Exposure to UV light can cause thymine dimers to form in DNA. Which repair system is primarily responsible for removing these dimers?

Accepted Answer

Nucleotide excision repair

Question 14

Which of the following best explains why most cancer cells can divide indefinitely?

Accepted Answer

They have active telomerase, which maintains telomere length.

Question 15

A scientist observes that a cell line can divide far more times than normal somatic cells. Which molecular feature would most likely explain this observation?

Accepted Answer

Active telomerase enzyme

Question 16

Which of the following sequences correctly describes the order of events in nucleotide excision repair?

Accepted Answer

Error detection → DNA nicking → Nucleotide excision → Nucleotide replacement → DNA ligation

Question 17

Which of the following is a direct consequence if single-strand DNA-binding proteins (SSBPs) are nonfunctional during DNA replication?

Accepted Answer

Separated DNA strands will re-anneal, preventing replication.

Question 18

If a mutation prevents the removal of RNA primers from the lagging strand, what would be the result?

Accepted Answer

The DNA would contain short stretches of RNA.

Question 19

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

Accepted Answer

It synthesizes short RNA primers to provide a 3' end for DNA polymerase.

Question 20

A patient is exposed to a chemical that increases the rate of thymine dimer formation. Which cellular process will be most affected if the nucleotide excision repair system is defective?

Accepted Answer

DNA replication

DNA and the Gene: Synthesis and Repair – Study Notes

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