Question 1

Which DNA repair pathway is primarily responsible for correcting thymine dimers caused by UV radiation in human cells?

Accepted Answer

Nucleotide Excision Repair (NER)

Question 2

A patient with xeroderma pigmentosum is exposed to sunlight. Which molecular defect most directly explains their extreme sensitivity to UV light?

Accepted Answer

Defective nucleotide excision repair proteins

Question 3

During DNA replication, DNA polymerase incorporates an incorrect base. Which enzymatic activity allows the polymerase to remove this base and replace it with the correct one?

Accepted Answer

3’ to 5’ exonuclease activity

Question 4

Which of the following best describes the sequence of events in base excision repair (BER)?

Accepted Answer

Glycosylase removes the damaged base, endonuclease cuts the backbone, DNA polymerase fills the gap, ligase seals the nick

Question 5

A double-strand break in DNA can be repaired by two major pathways. Which pathway is more error-prone and why?

Accepted Answer

Non-Homologous End Joining (NHEJ), because it joins DNA ends without a template

Question 6

A mutation in the TP53 gene is most likely to result in which of the following cellular outcomes after DNA damage?

Accepted Answer

Uncontrolled cell division and increased cancer risk

Question 7

Which of the following is a direct consequence if DNA damage is not properly repaired?

Accepted Answer

Genome instability and oncogenesis

Question 8

A patient presents with multiple types of cancer at a young age. Genetic testing reveals a germline mutation in the TP53 gene. What syndrome does this patient most likely have?

Accepted Answer

Li-Fraumeni syndrome

Question 9

Which protein complex is responsible for recognizing mismatched bases during mismatch repair in eukaryotes?

Accepted Answer

MSH proteins

Question 10

Which of the following equations best represents the probability $$P of $$inheriting an autosomal recessive disorder if both parents are carriers?

Accepted Answer

$$P = 1/4$$

Question 11

A researcher uses CRISPR-Cas9 to induce a double-strand break in a gene. If the cell repairs the break using homology directed repair (HDR), what is the most likely outcome?

Accepted Answer

Precise gene correction or insertion using a template

Question 12

Which of the following best explains why individuals with xeroderma pigmentosum have a higher risk of skin cancer?

Accepted Answer

They cannot efficiently repair UV-induced DNA damage

Question 13

Which step in nucleotide excision repair (NER) involves the removal of a 25-30 base pair segment surrounding the lesion?

Accepted Answer

Excision by XPG and XPF proteins

Question 14

A cell with a defective p53 protein is exposed to ionizing radiation. Which of the following is the most likely outcome?

Accepted Answer

The cell will continue to divide with damaged DNA

Question 15

Which of the following is NOT a typical consequence of unrepaired DNA double-strand breaks?

Accepted Answer

Increased genome stability

Question 16

Which of the following best describes the role of DNA ligase in DNA repair?

Accepted Answer

It seals nicks in the DNA backbone by recreating the phosphodiester bond

Question 17

A mutation in which of the following genes is most commonly associated with xeroderma pigmentosum in the United States?

Accepted Answer

XPC

Question 18

Which repair pathway is most likely to be activated in response to oxidative base damage caused by reactive oxygen species?

Accepted Answer

Base Excision Repair (BER)

Question 19

Which of the following best explains why mutations in the p53 gene can lead to cancer?

Accepted Answer

p53 normally suppresses tumor formation by inducing cell cycle arrest or apoptosis after DNA damage

Question 20

A cell is unable to repair a double-strand break using homologous recombination due to a mutation in a key gene. Which alternative pathway will the cell most likely use, and what is a potential consequence?

Accepted Answer

Non-Homologous End Joining (NHEJ); increased risk of insertions or deletions

DNA Repair Pathways and Their Role in Genetics and Disease

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