Question 1

Which enzyme is responsible for relieving the twisting forces that occur ahead of the replication fork during DNA replication?

Accepted Answer

Topoisomerase

Question 2

Why does the end replication problem occur in eukaryotic chromosomes?

Accepted Answer

DNA polymerase cannot add nucleotides to the 5' end of the lagging strand without a primer.

Question 3

A mutation disables the proofreading function of DNA polymerase. What is the most likely consequence?

Accepted Answer

The error rate during DNA replication will increase to about one mistake per 10 million base pairs.

Question 4

Which of the following best describes the function of telomerase?

Accepted Answer

It extends the 3' end of the lagging strand using an RNA template it carries.

Question 5

A researcher exposes cells to UV light, causing thymine dimers to form. Which DNA repair mechanism is primarily responsible for correcting this damage?

Accepted Answer

Nucleotide excision repair

Question 6

If a cell's mismatch repair system is defective, what is the most likely outcome?

Accepted Answer

The cell will accumulate mutations due to uncorrected replication errors.

Question 7

Which of the following statements about telomeres is TRUE?

Accepted Answer

They consist of short, repeating stretches of bases and do not contain genes.

Question 8

In cancer cells, how is the block to unlimited cell division typically overcome?

Accepted Answer

By maintaining telomere length through continued production of telomerase.

Question 9

A scientist treats mouse cancer cells with a telomerase inhibitor. The cells respond by increasing telomerase production. What does this suggest about cancer cell regulation?

Accepted Answer

Cancer cells can upregulate telomerase expression to counteract inhibition.

Question 10

Which of the following best explains why DNA repair is halted during mitosis?

Accepted Answer

Repair enzymes could join chromosomes together at their telomeres, causing catastrophic chromosome fusions.

Question 11

A cell line is engineered to express high levels of telomerase, resulting in telomeres of 24,000 base pairs. What is a possible consequence observed in research?

Accepted Answer

Cells become more sensitive to radiation over time.

Question 12

Which of the following sequences correctly describes the order of events in nucleotide excision repair?

Accepted Answer

Damage recognition, removal of damaged DNA, synthesis using intact strand, ligation

Question 13

If the error rate of DNA polymerase without proofreading is $$1 	imes 10$$^{-5}$$ per base pair, and proofreading reduces it to 1$$ 	imes $$10^{-7}$$, what is the fold reduction in error rate due to proofreading?

Accepted Answer

$$100$$

Question 14

Which enzyme is responsible for removing RNA primers and replacing them with DNA during lagging strand synthesis?

Accepted Answer

DNA polymerase I

Question 15

A patient has a genetic disorder that disables mismatch repair enzymes. Which type of mutation is most likely to accumulate in their cells?

Accepted Answer

Base substitution mutations

Question 16

Which of the following is a direct result of telomere shortening in somatic cells?

Accepted Answer

Cells eventually stop dividing and enter G$$_0$$ phase.

Question 17

Which of the following best explains why telomerase is not active in most somatic cells?

Accepted Answer

To limit the number of cell divisions and prevent uncontrolled growth.

Question 18

A scientist observes that a cell has a high rate of chromosome fusion during mitosis. Which DNA repair process is most likely malfunctioning?

Accepted Answer

Double-strand break (DSB) repair

Question 19

Which of the following is a key difference between proofreading and mismatch repair?

Accepted Answer

Proofreading occurs during DNA synthesis, while mismatch repair occurs after DNA synthesis is complete.

Question 20

If a cell switches from using telomerase to an ALT (Alternative Lengthening of Telomeres) system, what is the most likely outcome?

Accepted Answer

The cell can continue to maintain telomere length and divide.

DNA Synthesis and Repair: Telomeres, Telomerase, and DNA Repair Mechanisms

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