$$\text{Lactose} + \text{H}_2\text{O} \xrightarrow{\beta\text{-Galactosidase}} \text{Glucose} + \text{Galactose}$$

Question 1

Which of the following best describes the mechanism of feedback inhibition in the tryptophan biosynthetic pathway, as illustrated in the first image?

Accepted Answer

Tryptophan binds to the first enzyme in the pathway, inhibiting its activity and preventing further synthesis.

Question 2

In the second image, what is the primary difference between feedback inhibition and regulation of gene expression in the tryptophan pathway?

Accepted Answer

Feedback inhibition acts on enzyme activity, while gene expression regulation acts on the transcription of biosynthetic genes.

Question 3

Based on the third image, which of the following is NOT a component of a typical bacterial operon?

Accepted Answer

Enhancer

Question 4

Referencing the fifth image, how many polypeptides are produced from the trp operon mRNA?

Accepted Answer

$$5$$

Question 5

In the sixth image, what is the effect of the active repressor binding to the operator in the lac operon?

Accepted Answer

RNA polymerase cannot attach to the promoter, preventing transcription.

Question 6

According to the eighth image, what activates the trp repressor protein?

Accepted Answer

Binding of tryptophan to the repressor protein.

Question 7

In the ninth image, what happens when tryptophan acts as a corepressor?

Accepted Answer

The repressor protein becomes active, binds to the operator, and blocks transcription.

Question 8

Based on the tenth image, which enzyme catalyzes the breakdown of lactose into glucose and galactose?

Accepted Answer

Beta-galactosidase

Question 9

In the eleventh image, what is the role of the lacI gene product in the lac operon?

Accepted Answer

It acts as an active repressor that binds to the operator and prevents transcription.

Question 10

According to the twelfth image, what effect does allolactose have on the lac operon?

Accepted Answer

Allolactose binds to the repressor, inactivating it and allowing transcription of the operon.

Question 11

Which of the following best explains why the lac operon is considered an inducible operon?

Accepted Answer

It is normally inactive due to the repressor, and requires an inducer to inactivate the repressor and allow transcription.

Question 12

Which of the following equations correctly represents the reaction catalyzed by beta-galactosidase in the lac operon?

Accepted Answer

$$	ext{Lactose} + 	ext{H}_2	ext{O} \xrightarrow{\beta	ext{-Galactosidase}} 	ext{Glucose} + 	ext{Galactose}$$

Question 13

If a mutation caused the lac repressor to be unable to bind allolactose, what would be the effect on the lac operon?

Accepted Answer

The operon would never be expressed, even when lactose is present.

Question 14

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

Accepted Answer

The trp operon is repressible and is turned off when tryptophan binds to the repressor.

Regulation of Gene Expression: Prokaryotic and Eukaryotic Mechanisms

Study Guide - Practice Questions