Question 1

Which of the following best explains why bacteria regulate gene expression rather than transcribing all genes constitutively?

Accepted Answer

To conserve energy and resources by producing proteins only when needed.

Question 2

A mutation in the gene encoding the repressor protein of the lac operon causes the repressor to be unable to bind to the operator. What is the most likely outcome for the expression of the lac operon genes?

Accepted Answer

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

Question 3

Which of the following is an example of negative control of gene expression in bacteria?

Accepted Answer

A repressor protein binds to the operator, preventing RNA polymerase from transcribing the gene.

Question 4

In the context of the lac operon, what is the effect of high glucose and low lactose concentrations on the transcription of the operon?

Accepted Answer

Transcription is low because the repressor remains bound and CAP is inactive.

Question 5

Which of the following best describes the function of an operon in bacterial gene regulation?

Accepted Answer

A group of genes with related functions that are coordinately regulated and transcribed together.

Question 6

A researcher finds a mutant E. coli strain that cannot import lactose into the cell. Which gene is most likely mutated?

Accepted Answer

The gene encoding lactose permease.

Question 7

Which of the following statements about allosteric regulation of proteins is correct?

Accepted Answer

Allosteric regulation can change the shape of a protein, thereby activating or inhibiting its function.

Question 8

Which of the following best describes the role of cAMP and CAP in the regulation of the lac operon?

Accepted Answer

CAP binds to cAMP, and the complex binds to DNA to enhance transcription when glucose is low.

Question 9

Which of the following is an example of post-translational control of gene expression?

Accepted Answer

A protein is phosphorylated, altering its activity.

Question 10

A bacterial cell is grown in a medium containing both glucose and lactose. Which of the following best describes the expected expression of the lac operon?

Accepted Answer

The lac operon is not expressed because glucose inhibits cAMP production and prevents CAP activation.

Question 11

Which of the following equations best represents the relationship between gene expression and energy usage in a bacterial cell?

Accepted Answer

$E = \sum_{i=1}^{n} (e_i \cdot g_i)$

Question 12

The trp operon is an example of which type of gene regulation?

Accepted Answer

Negative control by a repressor that is activated by the end product (tryptophan).

Question 13

Which of the following scenarios best illustrates the concept of a regulon in bacterial gene regulation?

Accepted Answer

Multiple operons and genes are controlled by the same regulatory protein and respond to the same signal.

Question 14

Which of the following best describes translational control of gene expression?

Accepted Answer

Regulation of the stability and translation rate of mRNA into protein.

Question 15

A mutation causes the CAP protein to be unable to bind cAMP. What is the most likely effect on the lac operon when glucose is low and lactose is present?

Accepted Answer

The lac operon will have low expression because CAP cannot activate transcription.

Question 16

Which of the following is a real-world example of post-translational modification affecting protein function?

Accepted Answer

Phosphorylation of an enzyme in response to insulin signaling.

Question 17

Which of the following best explains why the presence of tryptophan in the environment leads to repression of the trp operon?

Accepted Answer

Tryptophan acts as a co-repressor, binding to the repressor protein and enabling it to block transcription.

Question 18

Which of the following is NOT a level at which gene expression can be regulated in bacteria?

Accepted Answer

Genomic control by altering DNA sequence in every cell cycle.

Question 19

Which of the following best describes the function of the AraC protein in the arabinose operon?

Accepted Answer

It acts as both an activator (in the presence of arabinose) and a repressor (in its absence).

Bacterial Gene Expression: Regulation and Control Mechanisms

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