Question 1

Which of the following best describes the mechanism of enzyme repression in the arginine (arg) operon of E. coli?

Accepted Answer

Arginine binds to the repressor protein, which then binds to the operator to block transcription.

Question 2

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

Accepted Answer

It acts as an inducer, binding to the repressor and preventing it from binding to the operator.

Question 3

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 4

A mutation in the CRP-binding site of the lac operon would most likely result in which of the following?

Accepted Answer

Inability of RNA polymerase to efficiently initiate transcription even when lactose is present and glucose is absent.

Question 5

Which of the following best explains diauxic growth observed in E. coli when both glucose and lactose are present?

Accepted Answer

E. coli preferentially uses glucose first, repressing the lac operon until glucose is depleted.

Question 6

Which of the following statements about the mal operon is correct?

Accepted Answer

The mal operon is activated by the binding of the maltose-activator protein to the activator-binding site in the presence of maltose.

Question 7

Which of the following is a key feature of a two-component regulatory system in bacteria?

Accepted Answer

It involves a sensor kinase and a response regulator.

Question 8

In the stringent response, what is the effect of the alarmone ppGpp on transcription?

Accepted Answer

It inhibits rRNA and tRNA synthesis by binding to RNA polymerase.

Question 9

Which of the following best describes attenuation in the trp operon?

Accepted Answer

It is a mechanism that allows the cell to fine-tune expression of tryptophan biosynthetic genes based on tryptophan availability.

Question 10

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

Accepted Answer

Low glucose, high lactose

Question 11

What is the function of the TrmBL1 protein in Archaea?

Accepted Answer

It can act as both a repressor and an activator depending on the presence of maltose.

Question 12

Which of the following best defines a regulon?

Accepted Answer

Multiple operons under the control of a single regulatory protein.

Question 13

In the presence of ammonia, what is the role of the NrpR protein in Archaea?

Accepted Answer

It represses transcription of genes needed to obtain ammonia.

Question 14

Which of the following is true regarding the mechanism of attenuation in the trp operon?

Accepted Answer

High tryptophan levels lead to the formation of a transcription termination structure in the leader region.

Question 15

Which of the following best describes the effect of glucose on the lac operon?

Accepted Answer

Glucose inhibits cAMP synthesis, preventing CRP from binding to the CRP-binding site and reducing lac operon expression.

Question 16

Which of the following is a correct sequence of events in a two-component regulatory system?

Accepted Answer

Sensor kinase autophosphorylates, transfers phosphate to response regulator, which then regulates gene expression.

Question 17

Which of the following is a likely outcome if a mutation prevents the trp repressor from binding tryptophan?

Accepted Answer

The trp operon will be constitutively expressed, regardless of tryptophan levels.

Question 18

Which of the following best explains why the mal operon requires an activator protein for transcription?

Accepted Answer

The promoter is weak and requires the activator to recruit RNA polymerase.

Question 19

Which of the following is a direct effect of the stringent response in E. coli?

Accepted Answer

Decreased synthesis of rRNA and tRNA, conserving resources during amino acid starvation.

Microbial Regulatory Systems: Mechanisms of Transcriptional Control in Bacteria and Archaea

Study Guide - Practice Questions