Question 1

Which experiment provided the most direct evidence that DNA, and not protein, is the hereditary material in viruses?

Accepted Answer

Hershey and Chase's radioactive labeling experiment with T2 bacteriophage

Question 2

In the Hershey-Chase experiment, what was the significance of finding radioactive DNA in the pellet after centrifugation?

Accepted Answer

It demonstrated that DNA is the genetic material transferred to the host.

Question 3

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

Accepted Answer

Each new DNA molecule consists of one old strand and one new strand.

Question 4

What role does DNA polymerase's exonuclease activity play during DNA replication?

Accepted Answer

It removes incorrectly paired nucleotides during proofreading.

Question 5

A mutation in the gene encoding single-stranded binding proteins (SSBPs) would most likely result in which of the following problems during DNA replication?

Accepted Answer

Strands re-annealing before replication can occur

Question 6

Which enzyme is responsible for relieving supercoiling ahead of the replication fork during DNA replication?

Accepted Answer

Topoisomerase

Question 7

During lagging strand synthesis, which enzyme is required to join Okazaki fragments together?

Accepted Answer

DNA ligase

Question 8

Why do eukaryotic chromosomes require multiple origins of replication?

Accepted Answer

They are linear and much longer, so multiple origins speed up replication.

Question 9

Which of the following best explains why telomerase is important in certain cell types?

Accepted Answer

It adds repetitive DNA sequences to chromosome ends, preventing shortening during replication.

Question 10

A patient with xeroderma pigmentosum (XP) is highly sensitive to sunlight. This is because their cells are deficient in which DNA repair mechanism?

Accepted Answer

Nucleotide excision repair

Question 11

Which of the following equations correctly represents the directionality of DNA synthesis?

Accepted Answer

$$5' \rightarrow 3'$$

Question 12

If DNA polymerase makes an error and incorporates a mismatched base, which repair mechanism is most likely to correct this error immediately during replication?

Accepted Answer

Proofreading by DNA polymerase

Question 13

Which of the following statements about Okazaki fragments is TRUE?

Accepted Answer

They are short DNA segments synthesized on the lagging strand.

Question 14

Which base pairing is correct according to Watson and Crick's model of DNA?

Accepted Answer

Adenine pairs with thymine

Question 15

A scientist grows E. coli in $$^{15}N$$ medium, then transfers them to $$^{14}N$$ medium for one generation. According to the semi-conservative model, what will be the composition of the DNA after one round of replication?

Accepted Answer

All DNA will be hybrid ($$^{15}N$$/$$^{14}N)$$

Question 16

Which of the following is a direct consequence of the inability to replace the RNA primer at the end of a linear chromosome during lagging strand synthesis?

Accepted Answer

Chromosome length shortens with each round of replication.

Question 17

Which enzyme synthesizes the short RNA primer required for DNA polymerase to begin DNA synthesis?

Accepted Answer

Primase

Question 18

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

Accepted Answer

It is a multi-enzyme complex that coordinates the synthesis of both leading and lagging strands.

Question 19

Which DNA repair mechanism is most likely to correct a thymine dimer caused by UV radiation?

Accepted Answer

Nucleotide excision repair

Question 20

Which of the following is the correct chemical structure for a phosphodiester bond formation between two nucleotides in DNA?

Accepted Answer

$$	ext{Phosphate group} - O - 	ext{Sugar (3' carbon)}$$

DNA Replication and Repair: Key Experiments and Mechanisms

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