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

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

Question 1

Which of the following best describes the function of the operator in a bacterial operon?

Accepted Answer

It is a segment of DNA that controls the access of RNA polymerase to the genes, acting as an on-off switch.

Question 2

In the trp operon, what is the role of tryptophan in regulating gene expression?

Accepted Answer

Tryptophan acts as a corepressor that binds to the repressor, activating it to bind the operator and block transcription.

Question 3

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

Accepted Answer

Lactose present, glucose absent, high cAMP levels

Question 4

What would happen to the production of β-galactosidase in an E. coli cell with a mutation that prevents the lac repressor from binding to the operator?

Accepted Answer

β-galactosidase would be produced continuously, regardless of lactose presence.

Question 5

Which of the following best explains feedback inhibition in the tryptophan biosynthesis pathway?

Accepted Answer

The end product tryptophan binds to the first enzyme in the pathway, inhibiting its activity.

Question 6

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

Accepted Answer

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

Question 7

A mutation in the trpR gene results in a nonfunctional repressor protein. What is the most likely consequence for the trp operon?

Accepted Answer

The trp operon will be constitutively expressed, and enzymes for tryptophan synthesis will be produced even when tryptophan is abundant.

Question 8

Which of the following statements about the lac operon is TRUE?

Accepted Answer

The lac operon is usually off but can be induced to turn on in the presence of lactose.

Question 9

Which of the following best describes the difference between repressible and inducible operons?

Accepted Answer

Repressible operons are usually on and can be turned off by a corepressor, while inducible operons are usually off and can be turned on by an inducer.

Question 10

If both glucose and lactose are absent in the environment of E. coli, what is the expected state of the lac operon?

Accepted Answer

The lac operon will be repressed because the lac repressor is active and bound to the operator.

Question 11

Which of the following is a direct result of CRP (cAMP receptor protein) binding to the lac promoter?

Accepted Answer

The affinity of RNA polymerase for the promoter increases, leading to higher transcription rates.

Question 12

Which of the following best explains why grouping genes into an operon is advantageous for bacteria?

Accepted Answer

It enables coordinated control of functionally related genes with a single on-off switch.

Question 13

Which of the following statements about allosteric proteins in gene regulation is correct?

Accepted Answer

Allosteric proteins can change shape upon binding small molecules, altering their ability to bind DNA.

Question 14

Which of the following best describes the function of β-galactosidase in E. coli?

Accepted Answer

It hydrolyzes lactose into glucose and galactose.

Question 15

A researcher adds tryptophan to a culture of E. coli. Which of the following is the most immediate effect on the trp operon?

Accepted Answer

The trp repressor binds tryptophan, becomes active, and binds the operator to block transcription.

Question 16

Which of the following is an example of negative gene regulation?

Accepted Answer

The lac repressor binding to the operator to block transcription.

Question 17

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

Accepted Answer

Allolactose acts as an inducer, binding to the lac repressor and inactivating it.

Question 18

Which of the following is true regarding the regulation of gene expression in bacteria?

Accepted Answer

Gene expression can be regulated at both the level of enzyme activity and the level of enzyme production.

Gene Regulation in Bacteria: The Operon Model (trp and lac Operons)

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