Question 1

Which of the following best explains why DNA replication is described as 'semi-conservative'?

Accepted Answer

Each new DNA molecule consists of one parental strand and one newly synthesized strand.

Question 2

Which enzyme is responsible for relieving the tension caused by unwinding of the DNA double helix ahead of the replication fork?

Accepted Answer

Topoisomerase

Question 3

During DNA replication, why is the lagging strand synthesized in short fragments rather than continuously?

Accepted Answer

DNA polymerase can only add nucleotides to the 3' end, so synthesis must occur in segments as the fork opens.

Question 4

Which of the following best describes the function of telomeres in eukaryotic chromosomes?

Accepted Answer

They protect the ends of chromosomes from deterioration during replication.

Question 5

A scientist finds that a sample of DNA contains 30% adenine. According to Chargaff's rules, what percentage of the DNA is expected to be guanine?

Accepted Answer

$$20\%$$

Question 6

Which experiment provided strong evidence that DNA, and not protein, is the genetic material in phages?

Accepted Answer

Hershey-Chase experiment using radioactive phosphorus and sulfur

Question 7

Which of the following statements about DNA polymerase is correct?

Accepted Answer

It adds nucleotides only to the free 3' hydroxyl end of a growing DNA strand.

Question 8

What is the role of primase during DNA replication?

Accepted Answer

It synthesizes a short RNA primer to provide a starting point for DNA polymerase.

Question 9

Which of the following best describes the antiparallel nature of DNA?

Accepted Answer

The two strands run in opposite directions: one 5' to 3', the other 3' to 5'.

Question 10

A mutation causes a cell to lack functional DNA ligase. Which process would be most directly affected?

Accepted Answer

Joining of Okazaki fragments on the lagging strand

Question 11

Which of the following is a direct consequence of the inability of DNA polymerase to complete the 5' ends of linear DNA molecules?

Accepted Answer

Progressive shortening of chromosomes with each cell division

Question 12

Which of the following best explains why prokaryotes do not face the same end-replication problem as eukaryotes?

Accepted Answer

Prokaryotic chromosomes are circular, so they lack ends.

Question 13

Which of the following is NOT a function of DNA polymerase during DNA replication?

Accepted Answer

Unwinding the DNA double helix

Question 14

Which of the following best describes the chemical reaction that occurs when a nucleoside triphosphate is added to a growing DNA strand?

Accepted Answer

A phosphodiester bond forms, releasing pyrophosphate ($$PP_i)$$

Question 15

A cell is exposed to UV light, causing thymine dimers to form in its DNA. Which repair mechanism is most likely to fix this damage?

Accepted Answer

Nucleotide excision repair

Question 16

Which of the following statements about Okazaki fragments is correct?

Accepted Answer

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

Question 17

Which of the following best explains why the base composition of DNA varies between species?

Accepted Answer

Different species have unique sequences of DNA that reflect their evolutionary history.

Question 18

Which of the following is a direct result of the antiparallel structure of DNA during replication?

Accepted Answer

One strand is synthesized continuously, while the other is synthesized in fragments.

Question 19

Which protein is responsible for stabilizing single-stranded DNA during replication to prevent it from re-annealing?

Accepted Answer

Single-strand binding proteins

Question 20

A mutation in a cell prevents the removal of RNA primers from the lagging strand. Which enzyme is most likely defective?

Accepted Answer

DNA polymerase I

CH16 - DNA Structure, Replication, and Repair

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