Question 1

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

Accepted Answer

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

Question 2

In the presence of high glucose and low lactose, what is the expected state of the lac operon?

Accepted Answer

The operon is repressed due to the repressor binding the operator and low cAMP levels.

Question 3

Which of the following mutations would result in constitutive expression of the lac operon, even in the absence of lactose?

Accepted Answer

A mutation in the operator sequence that prevents repressor binding ($$lacO^C).$$

Question 4

Which of the following best explains why bacteria grow faster on glucose than on lactose, as shown in the growth curve?

Accepted Answer

Glucose inhibits cAMP production, preventing CAP from activating the lac operon.

Question 5

What is the effect of a super-repressor mutation ($$lacI^s) in $$the lac operon?

Accepted Answer

The repressor cannot bind allolactose, so the operon is always repressed.

Question 6

Which of the following is TRUE regarding the trp operon in E. coli?

Accepted Answer

It is a repressible operon, turned off when tryptophan is abundant.

Question 7

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

Accepted Answer

It acts as an activator, increasing RNA polymerase affinity for the promoter.

Question 8

A bacterial cell is placed in an environment with low glucose and high lactose. What is the expected outcome for the lac operon?

Accepted Answer

High cAMP, CAP bound, repressor not bound, operon ON.

Question 9

Which of the following is a key difference between negative and positive regulation of gene expression in bacteria?

Accepted Answer

Negative regulation involves repressors blocking transcription, while positive regulation involves activators enhancing transcription.

Question 10

Which of the following best describes the effect of an inducer on a negatively regulated operon?

Accepted Answer

The inducer binds to the repressor, causing it to release from the operator and allow transcription.

Question 11

Which of the following equations correctly represents the relationship between glucose, cAMP, and CAP binding in the lac operon?

Accepted Answer

$$	ext{High glucose} ightarrow 	ext{Low cAMP} ightarrow 	ext{CAP not bound}$$

Question 12

A mutation in the CAP binding site of the lac operon would most likely result in which phenotype?

Accepted Answer

The operon cannot be efficiently activated in low glucose, even if lactose is present.

Question 13

Which of the following best explains why the lac operon is described as polycistronic?

Accepted Answer

It produces a single mRNA that encodes multiple proteins.

Question 14

Which of the following is a direct result of the binding of tryptophan to the trp repressor?

Accepted Answer

The repressor is activated and binds the operator, blocking transcription.

Question 15

Which of the following best describes the function of alternative sigma factors in bacteria?

Accepted Answer

They allow RNA polymerase to recognize different sets of promoters, activating groups of genes.

Question 16

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

Accepted Answer

Low glucose, high lactose

Question 17

Which of the following is a real-world application of understanding the lac operon system?

Accepted Answer

Engineering bacteria to produce recombinant proteins only in the presence of an inducer.

Gene Regulation in Bacteria: The Lac and Trp Operons CH 12 pt1/2

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