Q: Which equation best represents the process of DNA synthesis during excision repair, where a stretch of nucleotides is replaced?

$$\text{Damaged DNA} + \text{DNA polymerase} + \text{dNTPs} \rightarrow \text{Repaired DNA}$$

Question 1

Which DNA repair mechanism is most likely to introduce mutations during the repair of double-strand breaks (DSBs) in mammalian cells?

Accepted Answer

Non-homologous end joining (NHEJ)

Question 2

A patient with Xeroderma Pigmentosum (XP) is highly sensitive to sunlight. This condition is primarily due to a defect in which DNA repair pathway?

Accepted Answer

Nucleotide excision repair

Question 3

Which enzyme is responsible for repairing UV-induced pyrimidine dimers in bacteria through photoreactivation?

Accepted Answer

Photolyase

Question 4

During mismatch repair in E. coli, how does the system distinguish the newly synthesized strand from the template strand?

Accepted Answer

By nicks present due to Okazaki fragments

Question 5

Which DNA repair pathway is most likely to be used when a replication fork encounters a bulky DNA lesion that blocks progression?

Accepted Answer

Translesion synthesis

Question 6

What is the main difference between base excision repair (BER) and nucleotide excision repair (NER)?

Accepted Answer

BER removes a single damaged base, while NER removes a short stretch of nucleotides surrounding the lesion.

Question 7

Which of the following is TRUE regarding transposons in the human genome?

Accepted Answer

Transposons are mobile DNA elements that can change their position within the genome.

Question 8

A DNA transposon is found to have terminal inverted repeats (TIRs) and an open reading frame (ORF) for transposase. What does this indicate about the transposon?

Accepted Answer

It is an autonomous transposon.

Question 9

Which repair system in E. coli involves the UvrA, UvrB, and UvrC proteins and is responsible for removing a wide array of DNA lesions?

Accepted Answer

Nucleotide excision repair

Question 10

Which of the following best describes the mechanism of replicative transposition?

Accepted Answer

The transposon is copied and the new copy is inserted at a new site, increasing the number of elements.

Question 11

Which DNA repair pathway uses a homologous chromosome as a template to accurately repair double-strand breaks?

Accepted Answer

Homologous recombination repair (HRR)

Question 12

Which of the following is a consequence of non-homologous end joining (NHEJ) in DNA repair?

Accepted Answer

It is error-prone and can lead to mutations or deletions.

Question 13

Which repair system is responsible for correcting mispaired bases that arise during DNA replication?

Accepted Answer

Mismatch excision repair

Question 14

A scientist observes that a DNA lesion does not grossly distort the overall structure but is detected during replication. Which repair system is most likely to recognize and repair this lesion?

Accepted Answer

Mismatch excision repair

Question 15

Which of the following is a common feature shared by all excision repair systems?

Accepted Answer

They remove the damaged region and re-synthesize DNA using the complementary strand as a template.

Question 16

Which equation best represents the process of DNA synthesis during excision repair, where a stretch of nucleotides is replaced?

Accepted Answer

$$	ext{Damaged DNA} + 	ext{DNA polymerase} + 	ext{dNTPs} ightarrow 	ext{Repaired DNA}$$

Question 17

Which of the following statements about retrotransposons is correct?

Accepted Answer

Retrotransposons use an RNA intermediate to move within the genome.

Question 18

A mutation causes a DNA lesion that physically impedes replication. Which repair system is most likely to be activated?

Accepted Answer

Nucleotide excision repair

Question 19

Which of the following is NOT a step in the nucleotide excision repair pathway in E. coli?

Accepted Answer

Direct ligation of the damaged DNA without removal

Question 20

Which repair system is most likely to be used when a single-strand break occurs in DNA?

Accepted Answer

Direct reversal repair by ligation

DNA Repair Mechanisms and Transposable Elements

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