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, allowing the repressor to bind to the operator and 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 scenarios would result in maximal expression of the lac operon?

Accepted Answer

Low glucose, high lactose

Question 4

What is the function of the CRP-cAMP complex in the regulation of the lac operon?

Accepted Answer

It acts as an activator, facilitating RNA polymerase binding to the promoter.

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, then switches to lactose after glucose is depleted.

Question 6

Which statement about the mal operon in E. coli is correct?

Accepted Answer

The mal operon is activated by the binding of maltose to the MalT activator protein, which then binds to the activator-binding site.

Question 7

A mutation in the gene encoding the repressor protein of the arg operon results in a nonfunctional repressor. What is the most likely outcome?

Accepted Answer

The arg operon will be constitutively expressed, regardless of arginine levels.

Question 8

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 9

In the stringent response of E. coli, what is the role of the alarmone ppGpp?

Accepted Answer

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

Question 10

Which of the following best describes a regulon?

Accepted Answer

Multiple operons under the control of a single regulatory protein.

Question 11

In Archaea, what is the function of the TrmBL1 protein in the absence of maltose?

Accepted Answer

It represses genes for maltose uptake.

Question 12

Which of the following events would most likely trigger the stringent response in E. coli?

Accepted Answer

A shift from amino acid excess to amino acid limitation.

Question 13

What is the effect of glucose on cAMP levels in E. coli, and how does this impact the lac operon?

Accepted Answer

Glucose inhibits cAMP synthesis, reducing activation of the lac operon.

Question 14

Which of the following is an example of negative control of transcription?

Accepted Answer

Repression of the arg operon by ArgR in the presence of arginine.

Question 15

A mutation prevents the binding of the response regulator to DNA in a two-component system. What is the most likely consequence?

Accepted Answer

The target genes will not be regulated in response to environmental signals.

Question 16

Which of the following best describes catabolite repression?

Accepted Answer

Repression of an operon by the presence of a preferred carbon source, such as glucose.

Question 17

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

Accepted Answer

Decreased synthesis of rRNA and tRNA.

Question 18

In a scenario where both maltose and glucose are present, which operon(s) in E. coli would be most strongly expressed?

Accepted Answer

Neither mal nor lac operon, due to catabolite repression by glucose.

Question 19

Which of the following best explains the dual functionality of the TrmBL1 regulator in Pyrococcus furiosus?

Accepted Answer

It acts as a repressor for maltose uptake genes and as an activator for glucose synthesis genes, depending on the presence of maltose.

Regulation of Transcription in Microorganisms: Mechanisms and Examples

Study Guide - Practice Questions