Question 1

Which of the following best describes the role of tautomers in spontaneous DNA mutation during replication?

Accepted Answer

Tautomers are rare, alternate resonance structures of nitrogenous bases that can cause nonstandard base pairing, leading to replication errors.

Question 2

A patient is diagnosed with Huntington's Disease, which is associated with trinucleotide repeat expansion. What is the molecular mechanism underlying this disorder?

Accepted Answer

Strand slippage during DNA replication, causing DNA polymerase to replicate a short stretch of DNA twice.

Question 3

Which chemical mutagen is most likely to cause depurination by attaching to guanine?

Accepted Answer

Aflatoxin B$$_1$$

Question 4

What is the primary effect of intercalating agents such as ethidium bromide on DNA structure?

Accepted Answer

They insert themselves between adjacent bases, distorting the double helix and leading to additions or deletions of nucleotides.

Question 5

Which DNA repair mechanism directly reverses pyrimidine dimer formation using visible light?

Accepted Answer

Photoactive repair (light-dependent repair) via photolyase

Question 6

During base excision repair, which enzyme recognizes and removes a damaged base by cleaving the bond between the base and the sugar?

Accepted Answer

DNA glycosylase

Question 7

A cell exposed to UV radiation develops thymine dimers. Which repair pathway is most likely to be recruited if the damage stalls transcription?

Accepted Answer

Transcription-coupled nucleotide excision repair

Question 8

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

Accepted Answer

By the absence of methylation on the newly synthesized strand.

Question 9

Which protein detects mismatched bases during the mismatch repair process in E. coli?

Accepted Answer

MutS

Question 10

A double-strand break in DNA is repaired using the nonhomologous end-joining pathway. What is a major risk associated with this repair mechanism?

Accepted Answer

Loss of nucleotides from the broken ends and possible joining of incorrect DNA fragments.

Question 11

Which repair pathway uses the Rad51 protein to facilitate strand invasion during double-strand break repair?

Accepted Answer

Synthesis-dependent strand annealing (SDSA)

Question 12

What is the final structure formed during homologous recombination that must be resolved to separate the repaired DNA molecules?

Accepted Answer

Holliday junction

Question 13

Which of the following is a possible outcome of homologous recombination during DNA repair?

Accepted Answer

Permanent exchange of DNA between homologous chromosomes or gene conversion without exchange.

Question 14

A scientist exposes cells to nitrous acid (HNO$$_3). $$Which type of DNA damage is most likely to increase?

Accepted Answer

Deamination

Question 15

Which repair pathway is most versatile, able to correct a wide variety of DNA lesions, and is defective in individuals with xeroderma pigmentosum?

Accepted Answer

Nucleotide excision repair (NER)

Question 16

During base excision repair, what is the sequence of enzymatic steps following the removal of a damaged base?

Accepted Answer

AP endonuclease cleaves the backbone, a second enzyme removes the sugar, DNA polymerase synthesizes the new base, and DNA ligase seals the nick.

Question 17

Which of the following best explains why nonhomologous end-joining is considered error-prone?

Accepted Answer

It can result in loss of nucleotides and incorrect joining of DNA fragments due to lack of a template.

Question 18

Which process during meiosis is initiated by double-stranded breaks and involves the formation and resolution of Holliday junctions?

Accepted Answer

Homologous recombination

Question 19

A researcher introduces 5-bromodeoxyuridine (BrdU) into a cell culture. What is the most likely consequence for DNA replication?

Accepted Answer

BrdU, a base analogue of thymidine, will be incorporated into DNA and pair with adenine during replication.

DNA Damage, Repair, and Homologous Recombination (Chapter 17 Study Notes)

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