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

Question 1

Which of the following best describes the role of feedback inhibition in the tryptophan biosynthesis pathway in E. coli?

Accepted Answer

It inhibits the activity of the first enzyme in the pathway when tryptophan accumulates.

Question 2

What is the function of the operator in a bacterial operon?

Accepted Answer

It controls the access of RNA polymerase to the genes by serving as a binding site for the repressor.

Question 3

In the trp operon, what happens when tryptophan is present in the environment?

Accepted Answer

Tryptophan binds to the trp repressor, activating it and causing it to bind to the operator, shutting off transcription.

Question 4

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

Accepted Answer

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

Question 5

A mutation in the lac operator prevents the lac repressor from binding. What is the most likely outcome for the cell?

Accepted Answer

The cell will constitutively produce $$\beta-$$galactosidase, even in the absence of lactose.

Question 6

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

Accepted Answer

The lac operon is an inducible operon that is usually off unless lactose is present.

Question 7

Which of the following best describes the effect of allolactose on the lac operon?

Accepted Answer

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

Question 8

Which scenario would result in the highest rate of transcription of the lac operon?

Accepted Answer

Lactose present, glucose absent, high cAMP, active CRP.

Question 9

Which of the following is a key difference between repressible and inducible operons?

Accepted Answer

Repressible operons are usually on and can be turned off, while inducible operons are usually off and can be turned on.

Question 10

If an E. coli cell is placed in an environment lacking both glucose and lactose, what will happen to the lac operon?

Accepted Answer

The lac operon will not be transcribed because the lac repressor is active and no allolactose is present.

Question 11

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 12

Which protein acts as an activator in the positive regulation of the lac operon, and what molecule activates it?

Accepted Answer

CRP (cAMP receptor protein), activated by cAMP.

Question 13

Which of the following is TRUE regarding the regulation of enzyme production in the tryptophan pathway?

Accepted Answer

Enzyme production is regulated at the level of transcription by the trp operon.

Question 14

Which of the following best describes the role of a corepressor in gene regulation?

Accepted Answer

A corepressor binds to a repressor protein, activating it to bind to the operator and inhibit transcription.

Question 15

Which of the following equations best represents the effect of CRP binding on the rate of lac operon transcription?

Accepted Answer

$$	ext{Rate}_{	ext{lac}} = k \cdot [	ext{CRP}_{	ext{active}}]$$

Question 16

Which of the following is a consequence of the lac repressor being inactive due to allolactose binding, but CRP being inactive due to high glucose?

Accepted Answer

The lac operon is transcribed at a low rate.

Question 17

Which of the following is NOT a function of the lac operon genes?

Accepted Answer

Synthesis of tryptophan from a precursor molecule.

Question 18

Which of the following best describes the dual control of the lac operon?

Accepted Answer

It is regulated by both negative control (lac repressor) and positive control (CRP).

Question 19

Which scenario would result in the lowest expression of the lac operon?

Accepted Answer

Lactose absent, glucose present, low cAMP, inactive CRP.

Gene Regulation in Bacteria: The Operon Model and Its Mechanisms

Study Guide - Practice Questions