Question 1

Which of the following best describes the mechanism by which small RNAs (sRNAs) regulate gene expression in bacteria?

Accepted Answer

sRNAs base pair with mRNAs, affecting translation or stability of the mRNA.

Question 2

A riboswitch typically regulates gene expression by:

Accepted Answer

Changing the secondary structure of the 5' UTR in response to a small molecule, affecting translation initiation.

Question 3

Why is attenuation only found in prokaryotes and not in eukaryotes?

Accepted Answer

Transcription and translation are spatially separated in eukaryotes, preventing the coupling required for attenuation.

Question 4

In the tryptophan operon, what happens when tryptophan levels are high?

Accepted Answer

The ribosome quickly translates the leader peptide, causing formation of a terminator structure and premature transcription termination.

Question 5

Which of the following is an example of feedback inhibition in a metabolic pathway?

Accepted Answer

A product of the pathway binds to an allosteric site on the first enzyme, inhibiting its activity.

Question 6

Which of the following post-translational modifications can regulate enzyme activity?

Accepted Answer

Addition of a methyl group ($$CH_3)$$

Question 7

What is the role of the Hfq protein in sRNA-mediated regulation?

Accepted Answer

It acts as an RNA chaperone, helping sRNAs bind to their target mRNAs and protecting them from degradation.

Question 8

Which of the following scenarios best illustrates the function of isoenzymes in a branched metabolic pathway?

Accepted Answer

Each isoenzyme is regulated by a different end product, allowing fine-tuned control of each branch.

Question 9

A mutation in the leader sequence of the trp operon that removes the tandem tryptophan codons would most likely result in:

Accepted Answer

Loss of attenuation control, leading to constitutive expression of the operon.

Question 10

Which of the following best describes the mechanism of anti-sigma factor regulation?

Accepted Answer

Anti-sigma factors bind to sigma factors, preventing them from associating with RNA polymerase and initiating transcription.

Question 11

A cell is exposed to oxidative stress, and a specific sRNA is upregulated. What is the most likely effect of this sRNA?

Accepted Answer

It will base pair with a target mRNA, potentially blocking translation or promoting degradation.

Question 12

Which of the following is NOT a typical function of riboswitches?

Accepted Answer

Directly catalyzing the synthesis of small molecules.

Question 13

Which of the following equations best represents the reversible nature of feedback inhibition in enzyme regulation?

Accepted Answer

$$E + I \rightleftharpoons EI$$

Question 14

A researcher adds a small molecule that covalently modifies an enzyme, resulting in decreased activity. Which type of regulation is this?

Accepted Answer

Post-translational modification

Question 15

Which of the following best explains why riboswitches are considered remnants of the 'RNA world'?

Accepted Answer

They are catalytic RNAs that regulate gene expression without proteins.

Question 16

In the regulation of glutamine synthetase, what is the effect of uridylylation of the PII protein?

Accepted Answer

It stimulates glutamine synthetase adenyltransferase to deadenylate glutamine synthetase, increasing ammonia assimilation.

Question 17

A mutation causes an sRNA to perfectly base pair with its target mRNA. What is the most likely outcome?

Accepted Answer

The mRNA will be rapidly degraded by ribonucleases.

Question 18

Which of the following is a key difference between cis-acting riboswitches and trans-acting sRNAs?

Accepted Answer

sRNAs are spatially separated from their target mRNAs, while riboswitches are part of the same mRNA they regulate.

RNA-Based Regulation and Enzyme Activity Modification in Microbial Regulatory Systems

Study Guide - Practice Questions