Question 1

Which of the following best describes a constitutively expressed gene in bacteria?

Accepted Answer

A gene that is always expressed, regardless of environmental conditions.

Question 2

What is the primary function of the lacZ gene product in the lac operon?

Accepted Answer

It encodes $$\beta-$$galactosidase, which breaks down lactose into glucose and galactose.

Question 3

Which of the following scenarios will result in maximal expression of the lac operon in E. coli?

Accepted Answer

Glucose absent, lactose present

Question 4

What is the role of the lacI gene in the regulation of the lac operon?

Accepted Answer

It encodes a repressor protein that binds to the operator to inhibit transcription.

Question 5

Which of the following best describes the difference between cis-acting and trans-acting elements in gene regulation?

Accepted Answer

Cis-acting elements are DNA sequences that regulate genes on the same DNA molecule, while trans-acting elements are usually proteins that can diffuse and act on different DNA molecules.

Question 6

A mutation in the operator region of the lac operon prevents the repressor from binding. What is the most likely outcome?

Accepted Answer

The lac operon will be constitutively expressed, regardless of lactose presence.

Question 7

Which of the following is an example of negative control of gene expression?

Accepted Answer

A repressor protein binds to the operator, blocking RNA polymerase and inhibiting transcription.

Question 8

Why do bacteria such as E. coli prefer to metabolize glucose over lactose?

Accepted Answer

Glucose is a simpler sugar and can be directly used in glycolysis, while lactose must first be broken down.

Question 9

Which of the following best describes polycistronic mRNA in bacteria?

Accepted Answer

An mRNA that encodes multiple proteins, usually from genes in the same operon.

Question 10

If a mutation in the lacI gene produces a nonfunctional repressor protein, what will happen to the lac operon?

Accepted Answer

The lac operon will be constitutively expressed, regardless of lactose presence.

Question 11

Which enzyme is responsible for facilitating the entry of lactose into the bacterial cell?

Accepted Answer

Permease

Question 12

What is the effect of lactose binding to the lacI repressor protein?

Accepted Answer

It causes a conformational change that prevents the repressor from binding to the operator.

Question 13

Which of the following is NOT a structural gene of the lac operon?

Accepted Answer

lacI

Question 14

A researcher adds both glucose and lactose to a culture of E. coli. What will happen to the expression of the lac operon?

Accepted Answer

The lac operon will be repressed due to the presence of glucose.

Question 15

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

Accepted Answer

It is turned on only in the presence of an inducer (lactose).

Question 16

Which of the following statements about the central dogma of molecular genetics is correct?

Accepted Answer

Information flows from DNA to RNA to protein.

Question 17

Which of the following is a real-life application of understanding the lac operon system?

Accepted Answer

Designing antibiotics that target bacterial gene regulation.

Question 18

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

Accepted Answer

It is a DNA sequence where a repressor protein can bind to regulate transcription.

Question 19

Which of the following is a correct equation for the hydrolysis of lactose by $$\beta-$$galactosidase?

Accepted Answer

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

Regulation of Gene Expression in Bacteria: The lac Operon Model

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