Question 1

Which of the following best describes the main advantage of regulating gene expression at the level of transcription in bacteria?

Accepted Answer

It ensures that only necessary mRNAs are translated into proteins, saving energy and resources.

Question 2

In the lac operon, what is the role of the LacI protein?

Accepted Answer

It acts as a repressor that binds the operator and blocks RNA polymerase when lactose is absent.

Question 3

Which two conditions must be met for maximal expression of the lac operon in E. coli?

Accepted Answer

Low glucose and high lactose

Question 4

What is the effect of a mutation that changes the -35 hexamer of the lac promoter to the consensus sequence $$	ext{TTGACA}$$?

Accepted Answer

It strengthens the promoter, increasing transcription even without CAP.

Question 5

Which molecule acts as the inducer for the lac operon by binding to the LacI repressor?

Accepted Answer

Allolactose

Question 6

Why does the lac operon exhibit diauxic growth when both glucose and lactose are present?

Accepted Answer

Glucose represses the lac operon through catabolite repression, so lactose is only used after glucose is depleted.

Question 7

Which of the following best explains why transcriptional attenuation is not observed in eukaryotes?

Accepted Answer

Transcription and translation are not coupled in eukaryotes.

Question 8

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

Accepted Answer

The TrpR-tryptophan complex binds the operator, blocking transcription initiation.

Question 9

Which structure forms in the trp operon leader region when tryptophan is abundant, leading to transcription termination?

Accepted Answer

3:4 attenuator hairpin

Question 10

A mutation in the trp operon leader peptide changes both adjacent Trp codons to Ala codons. What is the most likely effect?

Accepted Answer

Attenuation will occur regardless of tryptophan levels.

Question 11

Which of the following best describes the function of a two-component signal transduction system in bacteria?

Accepted Answer

It senses environmental changes and alters gene expression via a sensor kinase and response regulator.

Question 12

How does antisense RNA (such as micF RNA) regulate gene expression in bacteria?

Accepted Answer

By binding to complementary mRNA and preventing translation.

Question 13

Which of the following is TRUE regarding the regulation of the ompF and ompC porin genes in E. coli?

Accepted Answer

OmpC is expressed at high osmotic pressure, while OmpF is expressed at low osmotic pressure.

Question 14

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

Accepted Answer

An RNA element that changes conformation upon ligand binding to regulate translation.

Question 15

Which equation best represents the relationship between cAMP and glucose in E. coli?

Accepted Answer

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

Question 16

Which of the following scenarios would result in the highest expression of the lac operon?

Accepted Answer

Low glucose, high lactose

Question 17

What is the primary reason that bacteria use both negative and positive regulation at the lac operon?

Accepted Answer

To tightly control expression, only producing enzymes when lactose is present and glucose is absent.

Question 18

Which of the following is a key difference between the regulation of the lac operon and the trp operon?

Accepted Answer

The lac operon is inducible, while the trp operon is repressible.

Question 19

Which of the following best explains why the leader peptide of the trp operon contains two adjacent tryptophan codons?

Accepted Answer

To ensure that attenuation only responds to tryptophan availability.

Regulation of Gene Expression in Bacteria

Study Guide - Practice Questions