Question 1

Which of the following best describes horizontal gene transfer in bacteria?

Accepted Answer

The movement of genes between cells other than by reproduction, such as transformation, transduction, or conjugation

Question 2

A missense mutation occurs in the active site of an enzyme. What is the most likely consequence?

Accepted Answer

The enzyme's activity may be altered, potentially reducing or abolishing its function

Question 3

Which type of mutation is most likely to result from the insertion or deletion of a single base pair in a coding region?

Accepted Answer

Frameshift mutation

Question 4

A bacterial strain is designated as hisC2. What does this notation indicate?

Accepted Answer

It is a mutant strain with a specific mutation in the hisC gene

Question 5

Which of the following best explains why silent mutations most often occur at the third base of a codon?

Accepted Answer

The genetic code is degenerate, so changes at the third base often do not alter the encoded amino acid

Question 6

Which of the following is an example of a selectable mutation in bacteria?

Accepted Answer

Antibiotic resistance

Question 7

A researcher uses replica plating to identify auxotrophic mutants. What is the principle behind this technique?

Accepted Answer

Colonies unable to grow on minimal medium lacking a specific nutrient are identified as auxotrophs

Question 8

Which of the following best describes a second-site revertant?

Accepted Answer

A mutation at a different site in the DNA that compensates for the original mutation, restoring the wild-type phenotype

Question 9

What is the role of suppressor tRNA in the context of nonsense mutations?

Accepted Answer

It recognizes the mutated stop codon and inserts an amino acid, potentially restoring protein function

Question 10

Which of the following mutagenic agents is most likely to cause frameshift mutations?

Accepted Answer

Intercalating agents such as acridines or ethidium bromide

Question 11

Ionizing radiation, such as X-rays, primarily damages DNA by:

Accepted Answer

Causing double- or single-stranded breaks and generating free radicals

Question 12

In Escherichia coli, which proteins regulate the SOS repair system?

Accepted Answer

LexA and RecA

Question 13

A mutation changes an adenine (A) to a guanine (G) in DNA. What type of mutation is this?

Accepted Answer

Transition

Question 14

Which of the following statements about mutation rates in microorganisms is correct?

Accepted Answer

DNA viruses have error rates 100–1000 times greater than prokaryotes

Question 15

A bacterial cell exposed to UV light is killed primarily due to:

Accepted Answer

Formation of pyrimidine dimers that disrupt DNA replication

Question 16

Which equation best represents the frequency of mutation per gene in a typical microorganism, given a mutation rate of $$10^{-7} to$$ $$10^{-6}$$ per kilobase and a gene size of 1 kb?

Accepted Answer

$$f = 10$$^{-7}$$ 	ext{ to } 10$$^{-6}$$

Question 17

A researcher treats bacteria with nitrosoguanidine, an alkylating agent. What is the most likely effect?

Accepted Answer

Induction of chemical modifications in DNA, leading to mutations

Question 18

Which of the following scenarios best illustrates a nonselectable mutation?

Accepted Answer

A bacterium loses pigment production, requiring laborious screening to identify

Question 19

A mutation in a tRNA gene changes its anticodon so it can recognize a stop codon. What is the potential consequence for the cell?

Accepted Answer

It may allow translation to continue past the stop codon, possibly restoring protein function

Question 20

Which of the following best describes the SOS repair system in bacteria?

Accepted Answer

It initiates multiple DNA repair processes, some error-free and some error-prone, especially when replication is stalled

Genetics of Bacteria: Mutations, Mutants, and Molecular Mechanisms

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