Question 1

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

Accepted Answer

It is a segment of DNA that acts as an on-off switch for gene expression by binding the repressor.

Question 2

In the trp operon, what happens when tryptophan levels are high?

Accepted Answer

The repressor binds to the operator, blocking transcription.

Question 3

Which of the following is true about the lac operon?

Accepted Answer

It is an inducible operon that is usually off unless an inducer is present.

Question 4

Which molecule acts as the inducer in the lac operon system?

Accepted Answer

Allolactose

Question 5

What is the effect of histone acetylation on gene expression in eukaryotes?

Accepted Answer

It opens chromatin structure, promoting transcription initiation.

Question 6

Which of the following best explains why eukaryotic mRNA is more long-lived than prokaryotic mRNA?

Accepted Answer

Eukaryotic mRNA is protected by a 5' cap and a poly-A tail.

Question 7

A mutation causes the lac repressor to be unable to bind allolactose. What is the most likely outcome?

Accepted Answer

The lac operon will always be off, even in the presence of lactose.

Question 8

Which of the following scenarios describes positive control of the lac operon?

Accepted Answer

cAMP binds to CRP, which then binds to the promoter and increases transcription.

Question 9

Which process allows a single gene to code for multiple proteins in eukaryotes?

Accepted Answer

Alternative RNA splicing

Question 10

A scientist discovers a bacterial operon that is only transcribed when a specific nutrient is absent. Which type of operon is this most likely to be?

Accepted Answer

Inducible operon

Question 11

Which of the following best describes feedback inhibition in a metabolic pathway?

Accepted Answer

The end product of the pathway inhibits the activity of an enzyme earlier in the pathway.

Question 12

What is the role of ubiquitin in protein regulation?

Accepted Answer

It marks proteins for degradation by proteasomes.

Question 13

Which of the following is a direct result of methylation of DNA in eukaryotes?

Accepted Answer

Long-term inactivation of genes

Question 14

Which of the following is true about general transcription factors in eukaryotes?

Accepted Answer

They are essential for the transcription of all protein-coding genes.

Question 15

If a mutation prevents the binding of CRP to the lac promoter, what is the most likely effect on the cell when glucose is scarce and lactose is present?

Accepted Answer

The lac operon will be transcribed at a low rate.

Question 16

Which of the following best explains why genes in heterochromatin are usually not expressed?

Accepted Answer

Heterochromatin is highly condensed, making DNA inaccessible to transcription machinery.

Question 17

Which of the following is a post-transcriptional modification that regulates gene expression?

Accepted Answer

Alternative RNA splicing

Question 18

A mutation causes the operator of the trp operon to be deleted. What is the most likely outcome?

Accepted Answer

The trp operon will be constitutively expressed, regardless of tryptophan levels.

Question 19

Which of the following best describes the function of mediator proteins in eukaryotic transcription?

Accepted Answer

They bring activators bound to enhancers into contact with general transcription factors at the promoter.

Question 20

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

Accepted Answer

Binding of a repressor to the operator to block transcription

Gene Regulation in Prokaryotes and Eukaryotes: Operons, Chromatin, and Transcriptional Control

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