Q: Which of the following equations correctly represents the conversion of lactose by β-galactosidase?

$$\text{Lactose} \xrightarrow{\beta\text{-galactosidase}} \text{Glucose} + \text{Galactose}$$

Question 1

Which of the following best describes a constitutive gene in bacteria?

Accepted Answer

A gene that is always expressed, regardless of environmental conditions.

Question 2

Transcriptional control of gene expression in bacteria is considered the most efficient because:

Accepted Answer

It prevents the synthesis of unnecessary mRNA and proteins.

Question 3

Which step in gene expression regulation provides the fastest cellular response?

Accepted Answer

Posttranslational control

Question 4

In the lac operon, what is the function of the lacI gene product?

Accepted Answer

It encodes a repressor protein that prevents transcription of lacZ and lacY when lactose is absent.

Question 5

A mutation in the lacO (operator) region that prevents the repressor from binding results in:

Accepted Answer

Constitutive expression of the lac operon regardless of lactose presence.

Question 6

Which of the following equations correctly represents the conversion of lactose by β-galactosidase?

Accepted Answer

$$	ext{Lactose} \xrightarrow{\beta	ext{-galactosidase}} 	ext{Glucose} + 	ext{Galactose}$$

Question 7

If an E. coli cell has a lacI- mutation, what will happen to the expression of the lac operon?

Accepted Answer

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

Question 8

Which of the following statements about the lac operon is TRUE?

Accepted Answer

The lac operon is regulated by both positive and negative control mechanisms.

Question 9

A merodiploid E. coli strain has one copy of lacO+ and one copy of lacOc. What is the expected phenotype for β-galactosidase expression?

Accepted Answer

Constitutive expression from the lacOc-linked operon, inducible expression from the lacO+-linked operon.

Question 10

Which of the following best describes a regulon in bacterial gene regulation?

Accepted Answer

A set of separate genes or operons controlled by the same regulatory protein.

Question 11

Which mechanism allows bacteria to rapidly respond to environmental changes by modifying protein activity?

Accepted Answer

Posttranslational control

Question 12

In negative control of transcription, what is the role of the repressor protein?

Accepted Answer

It binds to the operator and blocks RNA polymerase from transcribing the gene.

Question 13

Which of the following is a real-world example of post-transcriptional control in bacteria?

Accepted Answer

A cell modifies the stability of mRNA encoding a heat shock protein, leading to rapid changes in protein levels.

Question 14

Which of the following statements about the lacI+ allele is correct?

Accepted Answer

The lacI+ allele codes for a diffusible repressor protein that can regulate both linked and unlinked lac operons.

Question 15

Which of the following best explains why the lac operon is considered inducible?

Accepted Answer

Its expression is turned on in response to the presence of lactose.

Question 16

If a mutation causes the lac repressor to lose its ability to bind lactose, what would be the effect on lac operon expression?

Accepted Answer

The operon would never be expressed, even in the presence of lactose.

Question 17

Which of the following is a multi-step regulatory scenario involving the lac operon?

Accepted Answer

Lactose enters the cell, binds to the repressor, causing it to release from the operator, and transcription of lacZ and lacY occurs.

Question 18

Which of the following equations represents the relationship between gene expression and protein activity in bacteria?

Accepted Answer

$$	ext{DNA} \xrightarrow{	ext{Transcription}} 	ext{mRNA} \xrightarrow{	ext{Translation}} 	ext{Protein} \xrightarrow{	ext{Activation}} 	ext{Active Protein}$$

Question 19

Which of the following is a real-world application of global gene regulation in bacteria?

Accepted Answer

A bacterium coordinates the expression of dozens of genes to survive a heat shock event.

Control of Gene Expression in Bacteria: The lac Operon Model

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