$$\text{Lactose} + H_2O \rightarrow \text{Galactose} + \text{Glucose}$$

Question 1

Which of the following best describes the function of the lac operon in E. coli?

Accepted Answer

It enables the breakdown of lactose into glucose and galactose when lactose is present.

Question 2

What is the role of the Lac I repressor protein in the lac operon?

Accepted Answer

It binds to the operator region to inhibit transcription in the absence of lactose.

Question 3

Which mutation would result in constitutive expression of the lac operon, regardless of lactose presence?

Accepted Answer

A mutation in the operator site (Oc) preventing repressor binding.

Question 4

In the presence of both glucose and lactose, what happens to the transcription of the lac operon?

Accepted Answer

Transcription is diminished due to catabolite repression by glucose.

Question 5

Which equation correctly represents the enzymatic reaction catalyzed by β-galactosidase?

Accepted Answer

$$	ext{Lactose} + H_2O ightarrow 	ext{Galactose} + 	ext{Glucose}$$

Question 6

What is the effect of a super repressor (Is) mutation in the lac operon?

Accepted Answer

The repressor cannot bind lactose, so transcription is always repressed.

Question 7

Which of the following is a cis-acting element in bacterial gene regulation?

Accepted Answer

Operator site

Question 8

How does the presence of tryptophan affect the trp operon?

Accepted Answer

Tryptophan acts as a co-repressor, enabling the repressor to bind the operator and block transcription.

Question 9

Which of the following best describes attenuation in the trp operon?

Accepted Answer

A mechanism where transcription is prematurely terminated based on tryptophan levels and leader sequence structure.

Question 10

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

Accepted Answer

Lactose present, glucose absent, high cAMP levels.

Question 11

What is the function of the CAP-cAMP complex in the regulation of the lac operon?

Accepted Answer

It stabilizes the RNA polymerase-promoter complex, enhancing transcription.

Question 12

Which of the following is true about CRISPR loci in bacteria?

Accepted Answer

They contain repeated DNA sequences with nonrepetitive spacers matching phage genomes.

Question 13

A strain of E. coli has a mutation in the lacI gene such that the repressor cannot bind to the operator. What is the expected outcome?

Accepted Answer

The lac operon will be constitutively expressed.

Question 14

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

Accepted Answer

It is normally on but can be repressed by the presence of tryptophan.

Question 15

Which of the following is a trans-acting factor in bacterial gene regulation?

Accepted Answer

Repressor protein

Question 16

What is the effect of removing a newly acquired spacer from the CRISPR locus in Streptococcus thermophilus?

Accepted Answer

The bacterium loses resistance to the specific phage matching the spacer.

Question 17

Which of the following equations represents the relationship between cAMP concentration and glucose in catabolite repression?

Accepted Answer

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

Question 18

Which scenario best illustrates positive control of gene expression in bacteria?

Accepted Answer

CAP-cAMP complex binding to the CAP site to enhance transcription of the lac operon.

Question 19

Which of the following is NOT a component of the lac operon?

Accepted Answer

Tryptophan binding site

Regulation of Gene Expression in Bacteria: The lac Operon, trp Operon, Catabolite Repression, and CRISPR Systems

Study Guide - Practice Questions