Question 1

Which of the following best describes the function of the lac operon in E. coli?

Accepted Answer

It enables E. coli to break down lactose when glucose is not available.

Question 2

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

Accepted Answer

It provides the instructions for the repressor protein.

Question 3

In the absence of lactose, what happens to the lac operon?

Accepted Answer

The repressor binds the operator, preventing transcription.

Question 4

A mutation in the operator region ($O^c$) of the lac operon causes which of the following effects?

Accepted Answer

The operon is always ON, regardless of lactose presence.

Question 5

Which molecule acts as an inducer by binding to the lac repressor and allowing transcription of the lac operon?

Accepted Answer

Allolactose

Question 6

In an E. coli cell with low glucose and high lactose, which of the following best describes the state of the lac operon?

Accepted Answer

CAP is active, and the operon is strongly ON.

Question 7

Which of the following is TRUE regarding the trp operon in E. coli?

Accepted Answer

It is a repressible operon that is turned OFF when tryptophan is present.

Question 8

Attenuation in the trp operon is best described as:

Accepted Answer

A secondary regulatory mechanism that terminates transcription early when tryptophan is high.

Question 9

Which of the following best explains why the lac operon is not expressed when glucose is present, even if lactose is also present?

Accepted Answer

Low cAMP levels prevent CAP from binding and activating transcription.

Question 10

Which experimental evidence proved that the lac repressor is a protein?

Accepted Answer

Radioactive IPTG was found to bind to a protein in the cell extract.

Question 11

Which of the following is a key difference between eukaryotic and prokaryotic gene regulation?

Accepted Answer

Eukaryotic DNA is wrapped in chromatin, affecting transcription.

Question 12

Which of the following promoter elements is found in eukaryotes and is recognized by RNA polymerase II?

Accepted Answer

TATA box

Question 13

What is the function of enhancers in eukaryotic gene regulation?

Accepted Answer

They are DNA sequences that increase transcription by binding activators.

Question 14

A patient has a mutation that prevents alternative splicing of a gene. Which of the following is the most likely consequence?

Accepted Answer

The gene will produce only one protein variant, reducing functional diversity.

Question 15

Which of the following equations correctly represents the relationship between cAMP and CAP activation in the lac operon?

Accepted Answer

$[CAP_{active}] \propto [cAMP]$

Question 16

In a merozygote E. coli cell with one $O^c$ (constitutive operator) and one wild-type operator, what is the expected expression of the lac operon?

Accepted Answer

Only the operon with $O^c$ is always ON; the other is regulated normally.

Question 17

Which of the following best describes the effect of a $I^s$ (super-repressor) mutation in the lac operon?

Accepted Answer

The operon is always OFF, regardless of lactose.

Question 18

Which of the following is a consequence of misregulation of gene expression in humans?

Accepted Answer

It can cause diseases such as cancer or developmental disorders.

Question 19

Which of the following statements about silencers in eukaryotic gene regulation is correct?

Accepted Answer

Silencers are DNA sequences that bind repressors to decrease transcription.

Regulation of Gene Expression: Operons and Eukaryotic Control

Study Guide - Practice Questions