$$\text{End product} + \text{Enzyme 1} \rightarrow \text{Inhibition of Enzyme 1}$$

$$\text{CRP} + \text{cAMP} \rightarrow \text{Active CRP}$$

Question 1

Which of the following best describes the mechanism by which the trp operon is regulated in E. coli when tryptophan levels are high?

Accepted Answer

Tryptophan acts as a corepressor, activating the trp repressor, which binds to the operator and blocks transcription.

Question 2

In the lac operon, what is the role of allolactose?

Accepted Answer

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

Question 3

Which equation best represents feedback inhibition in a metabolic pathway?

Accepted Answer

$$	ext{End product} + 	ext{Enzyme 1} ightarrow 	ext{Inhibition of Enzyme 1}$$

Question 4

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

Accepted Answer

The trp operon will be continuously transcribed, regardless of tryptophan levels.

Question 5

Which of the following conditions will result in maximal transcription of the lac operon?

Accepted Answer

Lactose present, glucose absent, high cAMP levels

Question 6

What is the function of the operator region in an operon?

Accepted Answer

It acts as a binding site for the repressor protein, controlling access of RNA polymerase to the genes.

Question 7

Which equation describes the activation of CRP (catabolite activator protein) in response to low glucose?

Accepted Answer

$$	ext{CRP} + 	ext{cAMP} ightarrow 	ext{Active CRP}$$

Question 8

Which of the following statements about repressible and inducible operons is correct?

Accepted Answer

Repressible operons are usually on and can be turned off by a repressor; inducible operons are usually off and can be turned on by an inducer.

Question 9

If a cell is exposed to both lactose and glucose, what will happen to the transcription of the lac operon?

Accepted Answer

Transcription will occur at a low level because CRP is inactive due to low cAMP.

Question 10

Which of the following best explains why the trp operon is considered a repressible operon?

Accepted Answer

It is normally active but can be repressed when the end product (tryptophan) is abundant.

Question 11

Which of the following is a real-life example of feedback inhibition in cellular metabolism?

Accepted Answer

Tryptophan inhibits the activity of the first enzyme in its biosynthetic pathway when its concentration is high.

Question 12

Which equation represents the negative regulation of gene expression in the trp operon?

Accepted Answer

$$	ext{Tryptophan} + 	ext{trp Repressor} ightarrow 	ext{Active Repressor}$$

Question 13

Which of the following best describes the effect of high glucose levels on the lac operon?

Accepted Answer

High glucose leads to low cAMP, causing CRP to be inactive and reducing transcription of the lac operon.

Question 14

Which of the following is NOT a gene encoded by the lac operon?

Accepted Answer

lacI

Question 15

A student is studying a mutant E. coli strain in which the lac repressor cannot bind allolactose. What is the most likely outcome?

Accepted Answer

The lac operon will remain off even in the presence of lactose.

Question 16

Which of the following best describes the relationship between catabolic and anabolic pathways and operon regulation?

Accepted Answer

Inducible operons regulate catabolic pathways, while repressible operons regulate anabolic pathways.

Question 17

Which equation best represents the effect of allolactose on the lac operon?

Accepted Answer

$$	ext{Allolactose} + 	ext{lac Repressor} ightarrow 	ext{Inactive Repressor}$$

Question 18

Which of the following scenarios would result in the trp operon being transcribed?

Accepted Answer

Tryptophan is absent, and the repressor is inactive.

Question 19

Which of the following is a multi-step regulatory mechanism for gene expression in bacteria, as illustrated by the trp operon?

Accepted Answer

Regulation of enzyme activity by feedback inhibition and regulation of enzyme production by gene expression.

Regulation of Gene Expression in Prokaryotes: The Operon Model

Study Guide - Practice Questions