$$\text{Lactose} + H_2O \xrightarrow{\beta\text{-galactosidase}} \text{Glucose} + \text{Galactose}$$

Question 1

Which of the following best describes the function of the operator in the lac operon?

Accepted Answer

It is a sequence of DNA that acts as a binding site for the repressor.

Question 2

In E. coli, what happens to the lac operon when both glucose and lactose are present?

Accepted Answer

The operon is barely active because high glucose lowers cAMP, preventing CAP activation.

Question 3

Which enzyme is encoded by the lacZ gene in the lac operon?

Accepted Answer

β-galactosidase

Question 4

What is the effect of allolactose binding to the lac repressor?

Accepted Answer

It inactivates the repressor, preventing it from binding to the operator.

Question 5

Which of the following statements about polycistronic mRNA is correct?

Accepted Answer

It is found in prokaryotes and encodes multiple polypeptides per RNA molecule.

Question 6

Which gene product facilitates the entry of lactose into the bacterial cell?

Accepted Answer

Permease

Question 7

What is the role of cAMP in the regulation of the lac operon?

Accepted Answer

It binds to CAP, forming a complex that activates transcription.

Question 8

Which of the following is true about the lac operon in the absence of lactose?

Accepted Answer

The repressor is active, and the operon is off.

Question 9

Which equation correctly represents the conversion of lactose to glucose and galactose by β-galactosidase?

Accepted Answer

$$	ext{Lactose} + H_2O \xrightarrow{\beta	ext{-galactosidase}} 	ext{Glucose} + 	ext{Galactose}$$

Question 10

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

Accepted Answer

Ribosome

Question 11

What is the effect of glucose on cAMP levels in E. coli?

Accepted Answer

Glucose decreases cAMP levels.

Question 12

Which of the following best describes an inducible operon?

Accepted Answer

It is usually off and requires an inducer to turn on transcription.

Question 13

Which regulatory gene encodes the repressor protein for the lac operon?

Accepted Answer

lacI

Question 14

What is the primary function of transacetylase (lacA gene product) in the lac operon?

Accepted Answer

Removes toxic by-products of lactose digestion.

Question 15

Which of the following statements about gene expression in prokaryotes is correct?

Accepted Answer

Translation can begin before transcription has finished.

Question 16

Which scenario results in maximum transcription of the lac operon structural genes?

Accepted Answer

Lactose is present and glucose is absent.

Question 17

What is the effect of the CAP-cAMP complex on the lac operon?

Accepted Answer

It activates transcription by facilitating RNA polymerase binding to the promoter.

Question 18

Which of the following is a real-world consequence of catabolite repression in bacteria?

Accepted Answer

Bacteria will metabolize glucose before lactose.

Question 19

Which of the following best describes the relationship between the operator and the promoter in an operon?

Accepted Answer

The operator is positioned within or adjacent to the promoter.

Question 20

Which of the following equations represents the relationship between cAMP concentration and glucose availability?

Accepted Answer

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

Genetics & Molecular Biology: Key Concepts and Practice Questions

Study Guide - Practice Questions