Question 1

Which of the following best describes the role of constitutive genes in bacterial cells?

Accepted Answer

They are expressed all the time, regardless of cellular conditions.

Question 2

In the lac operon, what is the function of the lac Y gene product?

Accepted Answer

It transports lactose into the cell.

Question 3

Which molecule acts as the inducer for the lac operon in E. coli?

Accepted Answer

Allolactose

Question 4

A mutation in the operator region of the lac operon (Oc) leads to which phenotype?

Accepted Answer

Continuous production of lac enzymes, regardless of inducer presence.

Question 5

Which of the following best explains end-product repression in anabolic pathways?

Accepted Answer

The end product represses the transcription of genes encoding enzymes for its synthesis.

Question 6

If a bacterial cell has a mutation in the lac I gene that produces a superrepressor (I^s), what is the expected outcome?

Accepted Answer

Lac enzymes are never produced, regardless of inducer presence.

Question 7

Which of the following statements about polycistronic mRNA is correct?

Accepted Answer

It is an mRNA that codes for multiple polypeptides from a single transcript.

Question 8

Which equation best represents the hydrolysis of lactose by β-galactosidase?

Accepted Answer

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

Question 9

A mutation in the lac Z gene (Z-) would most likely result in which phenotype?

Accepted Answer

The cell cannot hydrolyze lactose into glucose and galactose.

Question 10

Which of the following is TRUE regarding the regulation of the lac operon?

Accepted Answer

The lac operon is transcribed only when the repressor is not bound to the operator.

Question 11

Which of the following best describes the difference between repression and feedback inhibition?

Accepted Answer

Repression affects gene transcription, while feedback inhibition affects enzyme activity.

Question 12

In a scenario where tryptophan concentration is high in a bacterial cell, what regulatory mechanism is most likely to occur?

Accepted Answer

Repression of tryptophan biosynthetic enzymes.

Question 13

Which of the following is a plausible consequence of a promoter mutation in the lac operon?

Accepted Answer

Decreased affinity of RNA polymerase and lower mRNA production.

Question 14

Which of the following best describes the role of allosteric regulation in the lac operon?

Accepted Answer

The repressor protein changes conformation upon binding allolactose, preventing it from binding the operator.

Question 15

Which of the following is TRUE about inducible operons?

Accepted Answer

They are turned on only in the presence of an inducer molecule.

Question 16

A researcher uses isopropylthiogalactoside (IPTG) in an experiment with E. coli. What is the purpose of IPTG in this context?

Accepted Answer

To induce transcription of the lac operon.

Question 17

Which of the following scenarios would result in continuous synthesis of lac operon enzymes?

Accepted Answer

Mutation in the operator region (Oc).

Question 18

Which of the following is the correct sequence of events for induction of the lac operon?

Accepted Answer

Lactose enters the cell → Allolactose binds repressor → Repressor releases operator → Transcription occurs

Question 19

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

Accepted Answer

It is transcribed only when an inducer molecule is present.

Regulation of Gene Expression: The lac Operon and Bacterial Gene Regulation

Study Guide - Practice Questions