Question 1

Which of the following best describes the difference between an inducible operon and a repressible operon in bacteria?

Accepted Answer

An inducible operon is usually OFF and can be turned ON by an inducer, while a repressible operon is usually ON and can be turned OFF by a corepressor.

Question 2

In the lac operon, what is the role of allolactose?

Accepted Answer

Allolactose acts as an inducer, binding to the repressor protein and causing it to dissociate from the operator.

Question 3

Which of the following scenarios would result in the highest level of lac operon transcription in E. coli?

Accepted Answer

Low glucose, high lactose

Question 4

What is the function of alternate sigma factors in bacterial cells?

Accepted Answer

They direct RNA polymerase to specific sets of promoters, allowing coordinated expression of genes in response to environmental changes.

Question 5

Which of the following best explains the mechanism of attenuation in the trp operon?

Accepted Answer

Attenuation is the process by which translation of the leader peptide affects the formation of a terminator or antiterminator hairpin in the mRNA, influencing transcription completion.

Question 6

A mutation in the operator region of the lac operon prevents the repressor from binding. What is the expected outcome?

Accepted Answer

The lac operon will be transcribed constitutively, regardless of lactose presence.

Question 7

Which of the following is a key feature of a riboswitch?

Accepted Answer

It is a segment of mRNA that binds small metabolites, causing a structural change that affects gene expression.

Question 8

Which of the following best describes the role of small RNAs (sRNAs) in bacterial gene regulation?

Accepted Answer

sRNAs base pair with mRNAs to modulate translation or stability, either blocking translation or protecting mRNA from degradation.

Question 9

Which of the following equations correctly represents the relationship between cAMP and glucose in catabolite repression?

Accepted Answer

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

Question 10

A bacterium is exposed to both glucose and lactose. Which of the following best describes the expected pattern of growth and lac operon expression?

Accepted Answer

The bacterium will first metabolize glucose (low lac operon expression), then switch to lactose metabolism (high lac operon expression) after glucose is depleted.

Question 11

Which sigma factor is primarily responsible for the heat shock response in E. coli?

Accepted Answer

$$\$$sigma^{32}$$

Question 12

What is the effect of a corepressor on a repressible operon such as the arg operon?

Accepted Answer

The corepressor binds to the repressor, enabling it to bind the operator and block transcription.

Question 13

Which of the following is true regarding regulons?

Accepted Answer

A regulon consists of multiple operons regulated by the same transcription factor.

Question 14

Which of the following best describes the mechanism by which sRNAs can increase translation of a target mRNA?

Accepted Answer

sRNAs bind to the mRNA, opening up the ribosome binding site (RBS) and allowing translation to proceed.

Question 15

Which of the following is a direct result of the formation of a terminator hairpin in the leader sequence of the trp operon?

Accepted Answer

Transcription of the trp operon is prematurely terminated.

Question 16

Which of the following best explains why glucose represses the lac operon even when lactose is present?

Accepted Answer

Glucose decreases cAMP levels, preventing activation of the CRP activator and thus reducing lac operon transcription.

Question 17

Which of the following is NOT a mechanism by which regulatory RNAs (sRNAs) can affect gene expression?

Accepted Answer

Recruiting RNA polymerase to the promoter.

Question 18

Which of the following statements about the default state of the lac and arg operons is correct?

Accepted Answer

The lac operon is usually OFF, and the arg operon is usually ON.

Question 19

Which of the following best describes the function of an activator protein in positive transcriptional control?

Accepted Answer

It binds to the activator-binding site and helps recruit RNA polymerase to the promoter.

Bacterial Regulatory Systems: Mechanisms of Gene Expression Control

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