Question 1

Which of the following best describes the role of the operator region in the lac operon?

Accepted Answer

It is a non-coding DNA sequence that regulates transcription by binding the repressor.

Question 2

A mutation in the lacI gene results in a nonfunctional repressor protein. What is the most likely consequence for the expression of the lac operon in the absence of lactose?

Accepted Answer

The lac operon will be constitutively expressed, even without lactose.

Question 3

Which of the following is a trans-acting factor in the regulation of the lac operon?

Accepted Answer

The lacI repressor protein

Question 4

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

Accepted Answer

Transcription is low because glucose inhibits cAMP production, reducing CAP activation.

Question 5

Which enzyme is encoded by the lacZ gene, and what is its function in lactose metabolism?

Accepted Answer

β-galactosidase; it hydrolyzes lactose into glucose and galactose

Question 6

Which of the following best explains why bacteria prefer glucose over lactose as an energy source?

Accepted Answer

Glucose inhibits cAMP production, preventing CAP activation and lac operon transcription.

Question 7

A bacterial cell has a mutation in the operator region of the lac operon such that the repressor cannot bind. What is the expected phenotype?

Accepted Answer

The lac operon is constitutively expressed, regardless of lactose presence.

Question 8

Which of the following is a correct description of cis-acting elements in gene regulation?

Accepted Answer

They are DNA sequences that must be on the same chromosome as the genes they regulate.

Question 9

The CAP protein is an example of an allosteric protein. Which molecule binds to CAP to activate it, and what is the effect?

Accepted Answer

cAMP; CAP binds to the promoter and promotes transcription.

Question 10

Which of the following elements of the lac operon are non-coding?

Accepted Answer

Promoter and operator

Question 11

If a bacterial cell contains a wild-type copy of the lacZ gene on an F' plasmid and a mutant lacZ gene on its chromosome, what will happen when lactose is present?

Accepted Answer

β-galactosidase will be produced due to complementation by the F' plasmid.

Question 12

Which of the following best describes polycistronic mRNA in the context of the lac operon?

Accepted Answer

A single mRNA that encodes multiple proteins from different genes.

Question 13

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

Accepted Answer

$$\mathrm{Lactose} + \mathrm{H}_2\mathrm{O} \rightarrow \mathrm{Glucose} + \mathrm{Galactose}$$

Question 14

Which of the following scenarios would result in maximal transcription of the lac operon?

Accepted Answer

Low glucose, high lactose

Question 15

A mutation in the CAP binding site of the lac operon promoter prevents CAP-cAMP binding. What is the expected effect on lac operon transcription when glucose is absent and lactose is present?

Accepted Answer

Transcription will be greatly reduced because CAP-cAMP cannot promote RNA polymerase binding.

Question 16

Which of the following statements about allosteric proteins is correct in the context of gene regulation?

Accepted Answer

Allosteric proteins change their activity in response to binding small molecules at a site other than the active site.

Question 17

Which of the following best explains the concept of inducible gene expression as seen in the lac operon?

Accepted Answer

Gene expression occurs only when a specific substrate (lactose) is present.

Question 18

Which experimental approach could be used to determine if a mutation in the operator region affects lac operon expression?

Accepted Answer

Measure β-galactosidase activity in cells with and without the operator mutation in the presence and absence of lactose.

Question 19

Which of the following is NOT a function of non-coding DNA elements in gene regulation?

Accepted Answer

Encoding enzymes for metabolic pathways

Gene Regulation in Prokaryotes: The Lac Operon Model and Lactose Metabolism: Nov 5

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