Question 1

Which of the following is a direct consequence of unrepaired DNA double-strand breaks in human cells?

Accepted Answer

Genomic instability leading to cancer

Question 2

A patient is exposed to UV radiation, resulting in the formation of cyclobutane pyrimidine dimers. Which DNA repair mechanism is primarily responsible for correcting this type of damage in human cells?

Accepted Answer

Nucleotide excision repair

Question 3

Which enzyme system in E. coli recognizes the newly synthesized DNA strand during mismatch repair by detecting the lack of methylation at $$5'	ext{-}GATC$$ sites?

Accepted Answer

MutHLS complex

Question 4

A researcher observes that a cell line is unable to repair 8-oxoguanine lesions, leading to increased mutations. Which enzyme is most likely defective in these cells?

Accepted Answer

OGG1 DNA glycosylase

Question 5

Which of the following best describes the function of transposase in bacterial cells?

Accepted Answer

It catalyzes the movement of transposable elements within the genome.

Question 6

In the Holliday model for homologous recombination, what is the key intermediate structure formed after strand invasion and ligation?

Accepted Answer

Holliday junction

Question 7

A mutation in the BRCA1 gene impairs which DNA repair process, increasing the risk for breast and ovarian cancer?

Accepted Answer

Homologous recombination repair of double-strand breaks

Question 8

Which of the following is a real-life application of the CRISPR-Cas9 system?

Accepted Answer

Site-specific gene knockout in mammalian cells

Question 9

During antibody gene rearrangement, which proteins catalyze the double-strand breaks necessary for V and J segment recombination?

Accepted Answer

RAG1 and RAG2

Question 10

A cell is exposed to a methylating agent, resulting in the formation of $$O^6-$$methylguanine. If this lesion is not repaired, what is the most likely consequence during DNA replication?

Accepted Answer

Misincorporation of thymine opposite the lesion, leading to mutation

Question 11

Which DNA repair pathway is most likely to be activated in response to oxidative damage resulting in 8-oxoguanine formation?

Accepted Answer

Base excision repair

Question 12

A scientist is studying a bacterial strain that cannot repair mismatches after DNA replication. Which of the following proteins is most likely mutated in this strain?

Accepted Answer

MutS

Question 13

Which of the following best explains how gene amplification can occur via unequal crossing over?

Accepted Answer

Homologous recombination between misaligned repeated sequences, resulting in duplication of a gene segment

Question 14

Which of the following is a key difference between simple and complex bacterial transposons?

Accepted Answer

Simple transposons encode only transposase, while complex transposons encode transposase and additional proteins such as antibiotic resistance factors.

Question 15

Which of the following best describes the process of daughter-strand gap repair in bacteria?

Accepted Answer

The newly synthesized DNA uses the undamaged parental strand as a template to fill in gaps left opposite lesions, allowing replication to continue.

Question 16

Which of the following is a function of nucleotide excision repair (NER) in human cells?

Accepted Answer

Repair of bulky DNA adducts and thymine dimers

Question 17

A retrovirus integrates its genome into the host chromosome using which of the following features?

Accepted Answer

Long terminal repeats (LTRs)

Question 18

Which of the following is a real-world consequence of defective mismatch repair in humans?

Accepted Answer

Increased risk of colorectal cancer

Question 19

Which of the following best describes the role of RecA protein in homologous recombination?

Accepted Answer

It promotes strand invasion and exchange during homologous recombination.

Question 20

Which of the following processes is responsible for generating antibody diversity during B cell development?

Accepted Answer

Gene rearrangement of V, D, and J segments

DNA Repair, Recombination, and Rearrangement: Key Concepts in Biochemistry

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