Question 1

A point mutation in a bacterial gene results in a codon change from UAU to UAA. What is the most likely effect of this mutation on the resulting protein?

Accepted Answer

It will result in a nonsense mutation, leading to premature termination of translation.

Question 2

Which of the following best describes the mechanism of homologous recombination in bacteria?

Accepted Answer

It requires sequence similarity between donor and recipient DNA, allowing exchange of genetic material.

Question 3

A researcher exposes E. coli to ultraviolet (UV) radiation. Which type of DNA damage is most likely to occur, and which repair mechanism is primarily responsible for correcting it?

Accepted Answer

Formation of thymine dimers; repaired by photoreactivation using photolyase.

Question 4

Which of the following statements about generalized and specialized transduction is correct?

Accepted Answer

Generalized transduction can transfer any gene from the donor, while specialized transduction transfers only specific genes near the prophage integration site.

Question 5

A laboratory strain of bacteria is exposed to a chemical mutagen that causes alkylation of guanine bases. What is the most likely molecular consequence of this exposure?

Accepted Answer

Mispairing of alkylated guanine with thymine during DNA replication.

Question 6

Which of the following best describes the difference between an insertion sequence (IS) and a transposon?

Accepted Answer

An IS contains only genes for transposition, while a transposon contains additional genes such as antibiotic resistance.

Question 7

In a bacterial transformation experiment, DNA is added to a culture of competent Streptococcus pneumoniae. Which of the following is required for successful natural transformation?

Accepted Answer

The recipient cells must be in a physiological state called competence.

Question 8

A bacterial cell with a defective DNA mismatch repair system is expected to show which of the following?

Accepted Answer

An increased rate of spontaneous mutation due to unrepaired replication errors.

Question 9

Which of the following best explains the concept of complementation in bacterial genetics?

Accepted Answer

Restoration of a wild-type phenotype by introducing a functional gene copy into a mutant.

Question 10

During conjugation in E. coli, what is the role of the F plasmid?

Accepted Answer

It encodes the machinery for pilus formation and DNA transfer to recipient cells.

Question 11

A scientist uses a transposon carrying a kanamycin resistance gene to mutagenize a bacterial population. What is the primary purpose of this approach?

Accepted Answer

To randomly disrupt genes and identify their function based on loss-of-function phenotypes.

Question 12

Which of the following equations correctly represents the calculation of mutation rate ($$\mu) $$per cell division?

Accepted Answer

$$\mu = \frac{	ext{Number of mutations}}{	ext{Number of cell divisions}}$$

Question 13

Which of the following is a key function of the CRISPR system in bacteria?

Accepted Answer

It provides adaptive immunity against invading genetic elements such as phages.

Question 14

A bacterium is infected by a phage, but the phage DNA is rapidly degraded. Which bacterial defense mechanism is most likely responsible?

Accepted Answer

Restriction-modification system that recognizes and cleaves foreign DNA.

Question 15

Which of the following scenarios best illustrates specialized transduction?

Accepted Answer

A temperate phage excises incorrectly from the host genome, carrying adjacent bacterial genes to a new host.

Question 16

Which of the following is a potential outcome if a frameshift mutation occurs early in a coding sequence?

Accepted Answer

The reading frame is altered, resulting in a completely different and likely nonfunctional protein.

Question 17

Which of the following best describes the process of laboratory transformation in bacteria?

Accepted Answer

Cells are made competent by chemical or physical treatment to take up exogenous DNA.

Question 18

A bacterial cell is exposed to a base analog, 5-bromouracil, during DNA replication. What is the most likely result?

Accepted Answer

Increased frequency of transition mutations due to mispairing.

Question 19

Which of the following statements about transposon mutagenesis is correct?

Accepted Answer

It allows for random insertion of a selectable marker into the genome, facilitating gene function studies.

Question 20

A bacterial strain is found to have a mutation in the recA gene. Which process is most likely to be impaired in this strain?

Accepted Answer

Homologous recombination and DNA repair.

Genetics of Bacteria: Mutations, Gene Transfer, Mobile DNA, and Defense Mechanisms

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