Question 1

Which of the following best describes the role of cAMP in the regulation of the lac operon in E. coli?

Accepted Answer

cAMP binds to CRP, forming a complex that enhances RNA polymerase binding to the promoter.

Question 2

If E. coli cells are grown in an environment with high glucose and high lactose, what will be the expected expression level of the lac operon?

Accepted Answer

Low, because high glucose results in low cAMP, reducing CRP activation.

Question 3

Which of the following equations correctly represents the relationship between glucose and cAMP levels in E. coli?

Accepted Answer

$$[\mathrm{cAMP}] \propto \frac{1}{[\mathrm{Glucose}]}$$

Question 4

A mutation prevents the CRP protein from binding cAMP. What is the most likely effect on lac operon expression when glucose is low and lactose is high?

Accepted Answer

The lac operon will not be expressed, even though lactose is present.

Question 5

Which of the following best explains why E. coli prefers to use glucose over lactose as an energy source?

Accepted Answer

Glucose represses the lac operon by decreasing cAMP levels, reducing transcription of lactose-utilizing genes.

Question 6

In an experiment, E. coli is placed in a medium with low glucose and low lactose. What is the expected state of the lac operon?

Accepted Answer

The operon is repressed because the repressor remains bound to the operator.

Question 7

Which of the following steps is NOT a mechanism by which glucose inhibits transcription of the lac operon?

Accepted Answer

By increasing the intracellular concentration of cAMP.

Question 8

A researcher adds a non-metabolizable analog of lactose to E. coli growing in high glucose. What is the expected effect on lac operon expression?

Accepted Answer

The operon will be expressed at low levels because high glucose keeps cAMP low.

Question 9

Which of the following best describes the function of the CRP-cAMP complex in lac operon regulation?

Accepted Answer

It binds to the promoter to enhance RNA polymerase binding and increase transcription.

Question 10

If both glucose and lactose are absent from the environment, what is the state of the lac operon?

Accepted Answer

The operon is repressed because the repressor is bound and RNA polymerase cannot initiate transcription.

Question 11

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

Accepted Answer

Low glucose, high lactose

Question 12

A mutation causes the lac repressor to be unable to bind the operator. What is the expected effect on lac operon expression in the presence of high glucose and no lactose?

Accepted Answer

The operon will be expressed at low levels due to low cAMP, but not fully repressed.

Question 13

Which of the following best explains why cAMP levels are high when glucose is low?

Accepted Answer

Low glucose increases the activity of adenylate cyclase, which synthesizes cAMP.

Question 14

In the context of the lac operon, what is the primary function of the operator region?

Accepted Answer

It is the binding site for the lac repressor protein.

Question 15

A strain of E. coli has a mutation that causes constitutive expression of the lac operon. Which of the following is the most likely cause?

Accepted Answer

A mutation in the operator that prevents repressor binding.

Question 16

Which of the following best describes the effect of high glucose and low lactose on the lac operon?

Accepted Answer

The operon is repressed due to both low cAMP and active repressor.

Question 17

Which of the following is a direct result of CRP-cAMP binding to the lac operon promoter?

Accepted Answer

Increased transcription of the lac operon genes.

Question 18

A scientist observes that the lac operon is not expressed even when lactose is present and glucose is absent. Which of the following could explain this observation?

Accepted Answer

A mutation in the CRP gene prevents CRP from binding cAMP.

Regulation of the Lac Operon: Glucose, cAMP, and Positive Control in Bacterial Gene Expression

Study Guide - Practice Questions

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