Question 1

Which of the following best describes the outcome of DNA replication in eukaryotic cells?

Accepted Answer

Two daughter double helices, each containing one parental and one newly synthesized strand

Question 2

The Meselson and Stahl experiment used isotopes of nitrogen to distinguish between old and new DNA strands. Why was nitrogen a suitable choice for this experiment?

Accepted Answer

Nitrogen is present in DNA but not in most other biomolecules, allowing selective labeling

Question 3

During which phase of the cell cycle does DNA replication occur?

Accepted Answer

S phase of interphase

Question 4

If the conservative model of DNA replication were correct, what would you expect to see after one round of replication in the Meselson-Stahl experiment?

Accepted Answer

One band at the original heavy DNA position and one at the light DNA position

Question 5

Which enzyme is responsible for unwinding the DNA double helix during replication, and what energy source does it use?

Accepted Answer

Helicase; uses ATP

Question 6

What is the role of DNA gyrase (a type of topoisomerase) during DNA replication in prokaryotes?

Accepted Answer

It relieves supercoiling ahead of the replication fork

Question 7

Why is DNA replication described as 'semi-discontinuous'?

Accepted Answer

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

Question 8

Which of the following best explains why the lagging strand is synthesized in Okazaki fragments?

Accepted Answer

DNA polymerase can only synthesize DNA in the 5' to 3' direction, but the two template strands are antiparallel

Question 9

Which enzyme removes RNA primers and replaces them with DNA during lagging strand synthesis in prokaryotes?

Accepted Answer

DNA polymerase I

Question 10

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

Accepted Answer

Single-stranded DNA would re-anneal or form secondary structures, impeding replication

Question 11

What is the function of telomerase in eukaryotic cells?

Accepted Answer

It extends the 3' end of the lagging strand template using an internal RNA template

Question 12

Which of the following diseases is associated with defects in telomerase activity, leading to premature telomere shortening?

Accepted Answer

Dyskeratosis congenita

Question 13

In prokaryotic DNA replication, what is the significance of the 'ori' region?

Accepted Answer

It is the origin of replication where DNA is first unwound and replication begins

Question 14

Which of the following statements about DNA polymerase III in prokaryotes is correct?

Accepted Answer

It synthesizes new DNA in the 5' to 3' direction and requires a primer to initiate synthesis

Question 15

A scientist observes that after two rounds of DNA replication in the Meselson-Stahl experiment, there are both intermediate and light DNA bands. Which model of DNA replication does this observation support?

Accepted Answer

Semi-conservative

Question 16

Which of the following equations correctly represents the formation of a phosphodiester bond during DNA synthesis?

Accepted Answer

$$dNTP + (DNA)_{n} \rightarrow (DNA)_{n+1} + PP_i$$

Question 17

Which of the following best explains why DNA at the origin of replication (ori) is typically AT-rich?

Accepted Answer

AT base pairs have two hydrogen bonds, requiring less energy to separate than GC pairs

Question 18

Which enzyme is responsible for joining Okazaki fragments on the lagging strand?

Accepted Answer

DNA ligase

Question 19

A patient is found to have abnormally high telomerase activity in their somatic cells. Which of the following is a likely consequence?

Accepted Answer

Increased risk of cancer due to unlimited cell division

DNA Replication: Mechanisms, Experiments, and Enzymology

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