Question 1

Which of the following best describes the mechanism of DNA uptake during Gram-positive bacterial transformation?

Accepted Answer

Single-stranded DNA enters the cell via a transformasome complex and recombines with the host chromosome.

Question 2

What is the primary role of the F factor in Escherichia coli conjugation?

Accepted Answer

It provides the genes necessary for pilus formation and DNA export during conjugation.

Question 3

Which of the following statements about generalized transduction is correct?

Accepted Answer

Any host gene can be transferred due to random packaging of host DNA into phage particles.

Question 4

A bacterium acquires a new antibiotic resistance gene via a transposon. Which of the following best explains how this could occur?

Accepted Answer

The transposon, carrying the resistance gene, moves from a plasmid to the chromosome via transposase-mediated insertion.

Question 5

Which of the following is a key difference between replicative and nonreplicative transposition?

Accepted Answer

Replicative transposition results in two copies of the transposon, while nonreplicative transposition results in only one copy at the new site.

Question 6

During specialized transduction, which genes are most likely to be transferred?

Accepted Answer

Genes adjacent to the prophage integration site.

Question 7

Which of the following best describes the function of inverted repeats in a transposon?

Accepted Answer

They serve as recognition sites for transposase during transposition.

Question 8

A researcher observes that a bacterial strain can no longer be transformed by external DNA. Which mutation could best explain this phenotype?

Accepted Answer

A mutation in the gene encoding the transformasome complex.

Question 9

Which of the following equations best represents the process of DNA recombination during transformation?

Accepted Answer

$$\mathrm{Donor\ DNA} + \mathrm{Recipient\ Chromosome} \rightarrow \mathrm{Recombinant\ Chromosome}$$

Question 10

Which of the following scenarios best illustrates the concept of surface exclusion in bacterial conjugation?

Accepted Answer

A donor cell cannot transfer its plasmid to another cell already carrying the same transmissible plasmid.

Question 11

Which of the following is NOT a characteristic of generalized transduction?

Accepted Answer

Transducing particles contain both phage and host DNA covalently joined.

Question 12

A patient is infected with a bacterial strain that has acquired a new metabolic pathway via a composite transposon. Which of the following best describes a composite transposon?

Accepted Answer

A transposon flanked by two insertion sequences, which may carry additional genes such as antibiotic resistance.

Question 13

Which of the following best explains why transposons are considered important in bacterial evolution?

Accepted Answer

They facilitate the horizontal transfer of genes, including those for antibiotic resistance.

Question 14

In the context of the lytic and lysogenic cycles of bacteriophage lambda, which event triggers the switch from lysogeny to lysis?

Accepted Answer

Induction by stress, leading to excision of the prophage and entry into the lytic cycle.

Question 15

Which of the following best describes the outcome of aberrant excision during specialized transduction?

Accepted Answer

A hybrid DNA molecule containing both phage and specific host genes is packaged.

Question 16

Which of the following is a direct result of the action of transposase?

Accepted Answer

Cleavage and integration of a transposon into a new DNA site.

Question 17

A scientist uses a pool of transposon mutants to study gene function in the mouse gut. What is the main advantage of this approach?

Accepted Answer

It allows for the identification of essential genes by comparing mutant abundance before and after selection.

Genetic Exchange Mechanisms in Bacteria: Transformation, Conjugation, Transduction, and Transposons

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