Question 1

Which phase of the cell cycle does DNA replication occur in eukaryotic cells?

Accepted Answer

S phase

Question 2

What is the main result of DNA replication?

Accepted Answer

Two identical double helices, each with one old and one new strand

Question 3

The Meselson-Stahl experiment used isotopes of nitrogen to distinguish between models of DNA replication. Which model was ruled out after the first round of replication?

Accepted Answer

Conservative

Question 4

If DNA replication were dispersive, what would you expect to see after two rounds of replication in the Meselson-Stahl experiment?

Accepted Answer

All DNA molecules would have a mixture of heavy and light nitrogen throughout

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

Why is the origin of replication (ori) in prokaryotes typically AT-rich?

Accepted Answer

AT pairs require less energy to separate than GC pairs

Question 7

Which enzyme relieves supercoiling ahead of the replication fork in prokaryotic DNA replication?

Accepted Answer

DNA gyrase

Question 8

What is the role of DNA polymerase III in prokaryotic DNA replication?

Accepted Answer

Main enzyme for synthesizing new DNA strands

Question 9

During lagging strand synthesis, which enzyme fills the gaps between Okazaki fragments after RNA primers are removed?

Accepted Answer

DNA ligase

Question 10

Which direction does DNA polymerase synthesize new DNA?

Accepted Answer

$$5' \rightarrow 3'$$

Question 11

What is the function of the RNA primer in DNA replication?

Accepted Answer

Provides a free $$3'-OH $$group for DNA polymerase to begin synthesis

Question 12

Which enzyme removes RNA primers and replaces them with DNA on the lagging strand?

Accepted Answer

DNA polymerase I

Question 13

What is the main problem encountered during replication of linear eukaryotic chromosomes at the telomeres?

Accepted Answer

The lagging strand cannot be fully replicated, leading to chromosome shortening

Question 14

How does telomerase solve the end-replication problem in eukaryotic cells?

Accepted Answer

It uses an internal RNA template to extend the $$3'$$ end of the lagging strand

Question 15

A patient with a mutation causing low telomerase activity is likely to experience which of the following?

Accepted Answer

Premature aging due to telomere shortening

Question 16

Which of the following best describes semi-discontinuous DNA replication?

Accepted Answer

Leading strand is synthesized continuously, lagging strand is synthesized in fragments

Question 17

Which of the following is a function of the replisome during DNA replication?

Accepted Answer

Coordinates the activities of multiple enzymes at the replication fork

Question 18

Which of the following equations represents the addition of a nucleotide to a growing DNA strand?

Accepted Answer

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

Question 19

Which of the following statements about Okazaki fragments is correct?

Accepted Answer

They are short DNA segments synthesized on the lagging strand

Question 20

A scientist isolates DNA from cells and finds that the DNA is composed of both heavy and light nitrogen after two rounds of replication. Which model of DNA replication does this support?

Accepted Answer

Semi-conservative

DNA Replication: Mechanisms, Models, and Enzymes

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