Question 1

During which phase of the eukaryotic cell cycle does DNA replication occur, and what is the significance of this timing for cell division?

Accepted Answer

S phase; it guarantees that each daughter cell receives an identical copy of DNA during mitosis or meiosis.

Question 2

Which of the following best describes the semiconservative nature of eukaryotic DNA replication?

Accepted Answer

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

Question 3

What is the primary reason eukaryotic chromosomes require multiple origins of replication?

Accepted Answer

Eukaryotic chromosomes are linear and much larger, so multiple origins ensure timely and complete replication.

Question 4

Which enzyme relieves the twisting strain ahead of the replication fork during DNA unwinding in eukaryotes?

Accepted Answer

Topoisomerase

Question 5

What is the role of single-stranded binding proteins (SSBs) during DNA replication?

Accepted Answer

They prevent reannealing and hairpin formation of unwound DNA strands.

Question 6

Which DNA polymerase is primarily responsible for synthesizing the leading strand in eukaryotic DNA replication?

Accepted Answer

DNA polymerase ε (epsilon)

Question 7

What is the function of the sliding clamp (PCNA) during DNA replication?

Accepted Answer

It keeps DNA polymerases attached to the DNA for high processivity.

Question 8

Why can’t the very end of the lagging strand be completely replicated in eukaryotic cells?

Accepted Answer

There is no space for primase to add the final RNA primer.

Question 9

How do telomerase and telomeres solve the end-replication problem in eukaryotic chromosomes?

Accepted Answer

Telomerase extends the 3′ end using its RNA template, and telomeres provide a buffer of repetitive DNA to protect coding regions.

Question 10

Which of the following sequences is the vertebrate telomere consensus repeat?

Accepted Answer

$$\mathrm{TTAGGG}$$

Question 11

A mutation in the gene encoding RNase H would most likely affect which step of lagging strand synthesis?

Accepted Answer

Removal of RNA primers from Okazaki fragments

Question 12

Which of the following best explains why prokaryotic cells do not face the end-replication problem?

Accepted Answer

Prokaryotic chromosomes are circular, so they have no ends to shorten.

Question 13

Which enzyme is responsible for joining Okazaki fragments into a continuous DNA strand on the lagging strand?

Accepted Answer

DNA ligase

Question 14

What is the role of the RNA component (TER) in telomerase?

Accepted Answer

It acts as a template for extending the DNA 3′ end by adding telomeric repeats.

Question 15

Which of the following steps occurs first during the initiation of eukaryotic DNA replication?

Accepted Answer

Loading of MCM-7 helicase onto DNA at each origin by the initiator complex (ORC)

Question 16

A researcher observes that a eukaryotic cell line has rapidly shortening chromosomes after each division. Which enzyme is most likely defective?

Accepted Answer

Telomerase

Question 17

Which of the following best describes the directionality of DNA synthesis during elongation?

Accepted Answer

DNA is synthesized in the 5′→3′ direction on both the leading and lagging strands.

Question 18

Which process ensures that both DNA polymerases (ε and δ) move together with the replication fork during eukaryotic DNA replication?

Accepted Answer

The lagging strand loops, allowing both polymerases to move together as one coordinated complex.

Question 19

A patient’s cells are found to have abnormally short telomeres and increased chromosomal instability. Which cellular process is most likely impaired?

Accepted Answer

Telomerase-mediated extension of chromosome ends

Question 20

Which of the following is a direct consequence if the sliding clamp (PCNA) is nonfunctional during DNA replication?

Accepted Answer

DNA polymerases frequently dissociate from the DNA, leading to incomplete or error-prone replication.

Eukaryotic DNA Replication: Mechanisms, Enzymes, and Chromosome End Maintenance

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