Question 1

Which of the following best describes a frameshift mutation and its likely effect on a protein product?

Accepted Answer

An insertion or deletion of nucleotides that alters the reading frame, often resulting in a completely different and nonfunctional protein.

Question 2

A researcher exposes bacterial cells to ultraviolet (UV) light. Which specific DNA lesion is most likely to form, and what is the primary repair mechanism for this lesion?

Accepted Answer

Thymine dimer; nucleotide-excision repair

Question 3

Which of the following statements about the Ames test is correct?

Accepted Answer

It uses a strain of Salmonella that cannot synthesize histidine to detect mutagenic compounds.

Question 4

Which of the following best explains why most mutations are considered neutral or harmful rather than beneficial?

Accepted Answer

Random changes in DNA are more likely to disrupt functional proteins than to improve them.

Question 5

A chemical mutagen causes the replacement of a cytosine with a uracil in DNA. Which DNA repair pathway is most likely to correct this error?

Accepted Answer

Base-excision repair

Question 6

Which of the following is a key difference between mismatch repair in bacteria and eukaryotes?

Accepted Answer

Bacteria use methylation to distinguish the old strand, while eukaryotes use nicks in the newly synthesized DNA.

Question 7

A patient is treated with a chemotherapy drug that is a nucleotide analog. What is the most likely molecular consequence of this treatment?

Accepted Answer

The analog is incorporated into DNA, causing abnormal base pairing and increased mutation rates.

Question 8

Which of the following best describes the process of positive selection for antibiotic-resistant mutants?

Accepted Answer

Only mutant cells with resistance survive and form colonies on media containing the antibiotic.

Question 9

A frameshift mutation is most likely to result from which of the following?

Accepted Answer

An insertion or deletion of one or two nucleotides

Question 10

Which of the following best ranks the types of mutations from greatest to least impact on protein structure and function?

Accepted Answer

Frameshift > Nonsense > Missense > Silent

Question 11

A scientist observes that a bacterial strain exposed to acridine orange shows a high frequency of nonfunctional proteins. What is the most likely explanation?

Accepted Answer

Acridine orange intercalates into DNA, causing insertions or deletions that result in frameshift mutations.

Question 12

Which of the following is a direct repair mechanism for UV-induced thymine dimers in bacteria, but not in humans?

Accepted Answer

Photoreactivation by photolyase

Question 13

During DNA replication, DNA polymerase incorporates an incorrect base. Which built-in activity of DNA polymerase helps prevent this error from becoming a permanent mutation?

Accepted Answer

3' → 5' exonuclease proofreading activity

Question 14

Which of the following best describes the SOS response in E. coli?

Accepted Answer

An emergency repair system that allows survival after severe DNA damage, even if mutations are introduced.

Question 15

A scientist is using negative selection to isolate tryptophan auxotrophs. Which of the following best describes the process?

Accepted Answer

Mutants are identified by their inability to grow on media lacking tryptophan, but growth on complete media.

Question 16

Which of the following is a likely outcome if a DNA repair system fails to distinguish between the old and new DNA strands during mismatch repair?

Accepted Answer

The wrong base may be removed, potentially fixing the mutation on both strands and making it permanent.

Question 17

Which of the following best explains why transcription errors in RNA are typically less harmful than mutations in DNA?

Accepted Answer

RNA errors are temporary and only affect a single transcript, while DNA mutations are permanent and heritable.

Question 18

A base-excision repair pathway is most likely to be activated in response to which of the following types of DNA damage?

Accepted Answer

Abnormal or chemically damaged bases, such as uracil in DNA

Question 19

Which of the following equations best represents the spontaneous mutation rate per base per replication in most organisms?

Accepted Answer

$10^{-8}$ 	ext{ to } 10^{-11}$

DNA Mutation and Repair: Mechanisms, Types, and Detection in Microbiology

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