Question 1

Which of the following best describes the 'end-replication problem' in eukaryotic cells?

Accepted Answer

The lagging strand cannot be fully replicated at the chromosome ends, leading to progressive telomere shortening.

Question 2

What is the sequence most commonly repeated in human telomeres?

Accepted Answer

$$	ext{TTAGGG}$$

Question 3

Which enzyme solves the end-replication problem by extending telomeres, and what is unique about its mechanism?

Accepted Answer

Telomerase; it is an RNA-dependent DNA polymerase with its own RNA template.

Question 4

A scientist observes that a certain cell type continues to divide indefinitely in culture. Which of the following is most likely true about these cells?

Accepted Answer

They express high levels of telomerase.

Question 5

Which of the following cell types typically maintain active telomerase expression in adult humans?

Accepted Answer

Germ cells

Question 6

What is the fate of a human somatic cell that has reached critically short telomere length?

Accepted Answer

It enters a state called senescence and stops dividing (Hayflick limit).

Question 7

Which of the following best explains why cancer cells often reactivate telomerase?

Accepted Answer

To maintain telomere length and enable unlimited cell division.

Question 8

A new drug, Imetelstat, is being tested in clinical trials. What is its mechanism of action?

Accepted Answer

It inhibits telomerase activity.

Question 9

Which of the following is a direct consequence of the removal of RNA primers at the very end of the lagging strand during DNA replication?

Accepted Answer

A single-stranded DNA overhang is left, leading to telomere shortening.

Question 10

Which three ribonucleotides in telomerase RNA would base pair with the DNA sequence $$	ext{GGG} at $$the 3' end of a chromosome?

Accepted Answer

$$	ext{CCC}$$

Question 11

Which of the following best describes the role of DNA mismatch repair (MMR) in cells?

Accepted Answer

It corrects errors that escape DNA polymerase proofreading after replication.

Question 12

In bacteria, how does the mismatch repair system distinguish the newly synthesized DNA strand from the template strand?

Accepted Answer

By the absence of methylation on the new strand.

Question 13

Which of the following is the correct order of steps in the mismatch repair (MMR) process?

Accepted Answer

Identify, nick, digest, replace, ligate

Question 14

Which DNA repair mechanism is primarily responsible for removing bulky DNA adducts caused by UV light exposure?

Accepted Answer

Nucleotide excision repair (NER)

Question 15

A patient is exposed to high levels of UV light and develops skin lesions. Which DNA repair pathway is most likely defective in this patient?

Accepted Answer

Nucleotide excision repair (NER)

Question 16

Which of the following best explains why DNA proofreading by DNA polymerase is essential for genome stability?

Accepted Answer

It reduces the error rate by removing mismatched nucleotides during synthesis.

Question 17

Which of the following is a source of endogenous DNA damage?

Accepted Answer

Deamination of cytosine

Question 18

If a mutation occurs in the MutS gene in bacteria, which DNA repair process will be directly affected?

Accepted Answer

Mismatch repair (MMR)

Question 19

A 100-year-old person has significantly shorter telomeres in their lymphocytes compared to a 20-year-old. What is the most likely explanation for this observation?

Accepted Answer

Telomeres shorten with each cell division due to incomplete lagging strand replication.

Telomeres, Telomerase, and DNA Repair Mechanisms: Study Notes for Genetics

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