Question 1

Which of the following best describes the mechanism by which cyclic AMP (cAMP) modulates catabolite repression in Escherichia coli?

Accepted Answer

cAMP binds to the catabolite activator protein (CAP), forming a complex that enhances RNA polymerase binding to certain promoters.

Question 2

A bacterial culture is shifted from a nutrient-rich medium to one lacking amino acids. Which molecule is rapidly synthesized to initiate the stringent response, and what is its effect?

Accepted Answer

ppGpp; it decreases rRNA and tRNA synthesis, conserving resources.

Question 3

During heat shock, bacteria produce a set of proteins known as heat shock proteins (HSPs). What is the primary function of these proteins?

Accepted Answer

They serve as chaperones to refold denatured proteins and prevent aggregation.

Question 4

Which of the following scenarios best illustrates catabolite repression in bacteria?

Accepted Answer

A bacterium represses the lac operon in the presence of glucose, even if lactose is available.

Question 5

Small RNAs (sRNAs) regulate gene expression in bacteria primarily by which of the following mechanisms?

Accepted Answer

Interacting with mRNA to alter its stability or translation efficiency.

Question 6

A riboswitch is best described as:

Accepted Answer

A segment of mRNA that binds a small molecule, causing a conformational change that affects gene expression.

Question 7

In the trp operon, attenuation is a regulatory mechanism that depends on which of the following?

Accepted Answer

The coupling of transcription and translation, allowing the ribosome to influence mRNA secondary structure.

Question 8

Which of the following equations correctly represents the relationship between cAMP and glucose concentration in E. coli?

Accepted Answer

$$[\mathrm{cAMP}] \propto \frac{1}{[\mathrm{glucose}]}$$

Question 9

A mutation in the gene encoding the sigma factor $$\$$sigma^{32}$$ in E. coli would most likely result in which phenotype?

Accepted Answer

Defective heat shock response due to failure to transcribe heat shock genes.

Question 10

Which of the following best explains how the stringent response helps bacteria survive during amino acid starvation?

Accepted Answer

By synthesizing ppGpp, which downregulates rRNA and tRNA synthesis, conserving resources.

Question 11

A researcher introduces a mutation that prevents the formation of the terminator hairpin in the leader region of the trp operon mRNA. What is the most likely effect on trp operon expression?

Accepted Answer

The operon will be constitutively expressed, even when tryptophan is abundant.

Question 12

Which of the following is a key difference between riboswitches and sRNAs in bacterial gene regulation?

Accepted Answer

Riboswitches are cis-acting elements within mRNA, while sRNAs are trans-acting molecules that interact with target RNAs.

Question 13

A bacterial cell is exposed to oxidative stress. Which regulatory system is most likely to be activated to protect cellular proteins?

Accepted Answer

Heat shock response, leading to increased expression of chaperones and proteases.

Question 14

Which of the following best describes the function of the leader peptide in the trp operon attenuation mechanism?

Accepted Answer

It allows the ribosome to sense tryptophan levels and influence the formation of transcriptional terminator or anti-terminator structures.

Question 15

A mutation in a riboswitch prevents it from binding its ligand. What is the most likely consequence for gene expression?

Accepted Answer

Gene expression will be unresponsive to changes in ligand concentration.

Question 16

Which of the following is a direct effect of ppGpp accumulation during the stringent response?

Accepted Answer

Decreased synthesis of tRNA and rRNA, slowing down protein synthesis.

Question 17

A bacterial cell with a defective sRNA that normally represses an outer membrane protein (OMP) will likely show which phenotype?

Accepted Answer

Increased levels of OMP due to lack of sRNA-mediated repression.

Question 18

Which of the following best explains why the heat shock response is considered a global regulatory system?

Accepted Answer

It coordinates the expression of multiple genes across the genome in response to stress.

Question 19

Which of the following is a real-world application of understanding riboswitches in bacteria?

Accepted Answer

Designing antibiotics that target riboswitches to disrupt essential gene expression.

Question 20

A bacterial mutant is unable to synthesize cAMP. Which of the following phenotypes would you expect?

Accepted Answer

Inability to activate catabolic operons when glucose is absent.

Microbial Regulatory Systems II: Global Control and RNA-Based Regulation

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