Question 1

Which of the following best describes the role of acyl homoserine lactone (AHL) in quorum sensing among Gram-negative bacteria?

Accepted Answer

AHL is a signaling molecule that accumulates as cell density increases, binding to activator proteins to regulate gene expression.

Question 2

A hospital patient develops a persistent lung infection with Pseudomonas aeruginosa. Which property of biofilms most likely contributes to the difficulty in treating this infection?

Accepted Answer

Biofilms prevent the penetration of antibiotics due to their extracellular polysaccharide matrix.

Question 3

Which of the following is a direct result of the accumulation of cyclic di-guanosine monophosphate (c-di-GMP) in bacterial cells?

Accepted Answer

Initiation of extracellular polysaccharide production and decreased flagellar function.

Question 4

A mutation changes a codon from UAC (tyrosine) to UAA (stop codon). What type of mutation is this, and what is the likely effect on the protein?

Accepted Answer

Nonsense mutation; the protein will be truncated and likely nonfunctional.

Question 5

Which process is illustrated when a bacteriophage accidentally packages host DNA and transfers it to another bacterium?

Accepted Answer

Generalized transduction

Question 6

What is the primary function of the RecA protein in homologous recombination?

Accepted Answer

RecA binds single-stranded DNA and mediates strand invasion during recombination.

Question 7

Which of the following best explains why UV radiation is effective at killing bacteria?

Accepted Answer

UV radiation forms pyrimidine dimers in DNA, disrupting replication and transcription.

Question 8

A researcher introduces a transposon carrying an antibiotic resistance gene into a bacterial culture. What is the most likely outcome for cells that survive on selective medium?

Accepted Answer

They have integrated the transposon into their chromosome, disrupting a gene and expressing antibiotic resistance.

Question 9

Which of the following statements about the CRISPR-Cas system is correct?

Accepted Answer

CRISPR-Cas provides adaptive immunity by storing fragments of viral DNA as spacers in the host genome.

Question 10

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

Accepted Answer

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

Question 11

A bacterial cell is exposed to both norepinephrine (a host hormone) and AI-3 (a bacterial autoinducer). What is the most likely outcome in a pathogenic E. coli strain?

Accepted Answer

Activation of sensor kinases, leading to increased toxin production.

Question 12

Which of the following is a key difference between generalized and specialized transduction?

Accepted Answer

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

Question 13

Which of the following events is most likely to result in a frameshift mutation?

Accepted Answer

Insertion of two base pairs into a coding sequence.

Question 14

What is the main advantage of horizontal gene transfer for bacterial populations?

Accepted Answer

It allows for rapid acquisition of new traits, increasing genetic diversity and adaptability.

Question 15

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

Accepted Answer

Uptake of free DNA from the environment and integration into the chromosome.

Question 16

A researcher observes that a bacterial strain can no longer form biofilms after insertion of a transposon. Which gene is most likely disrupted?

Accepted Answer

A gene encoding a flagellar hook protein.

Question 17

Which of the following is a characteristic of an Hfr (high frequency of recombination) bacterial cell?

Accepted Answer

It has the F plasmid integrated into its chromosome, allowing transfer of chromosomal genes during conjugation.

Question 18

Which of the following is true regarding the mechanism of conservative transposition?

Accepted Answer

The transposon is excised from the donor DNA and inserted into a new location, leaving a double-stranded break at the original site.

Microbial Regulatory Systems, Biofilm Formation, and Genetics of Bacteria

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