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

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

Accepted Answer

Lactose (specifically allolactose)

Question 5

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 6

Which experimental molecule was used to prove that the lac repressor is a protein?

Accepted Answer

IPTG

Question 7

How does the CAP-cAMP complex regulate the lac operon when glucose levels are low?

Accepted Answer

It increases the strength of RNA polymerase binding, enhancing transcription.

Question 8

Which of the following best explains why the trp operon is considered a repressible system?

Accepted Answer

It is turned OFF when tryptophan is present, as tryptophan acts as a corepressor.

Question 9

What is the function of attenuation in the trp operon?

Accepted Answer

It provides a second layer of regulation by terminating transcription early when tryptophan is abundant.

Question 10

Which of the following is TRUE about eukaryotic gene regulation compared to prokaryotic gene regulation?

Accepted Answer

Eukaryotic DNA is wrapped in chromatin, affecting gene expression.

Question 11

Which element is responsible for increasing transcription by binding specific transcription factors upstream of the core promoter in eukaryotes?

Accepted Answer

Enhancer

Question 12

A mutation that prevents the lac repressor from binding to the operator would result in which phenotype?

Accepted Answer

Constitutive expression of lacZ, lacY, and lacA

Question 13

Which of the following best describes the role of silencers in eukaryotic gene regulation?

Accepted Answer

They bind repressors and decrease transcription.

Question 14

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

Accepted Answer

Only the operon with the O^c mutant operator is constitutively expressed.

Question 15

Which equation correctly represents the relationship between cAMP and glucose concentration in E. coli?

Accepted Answer

$[cAMP] \propto \frac{1}{[glucose]}$

Question 16

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

Accepted Answer

Low glucose, high lactose

Question 17

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

Accepted Answer

Developmental disorders and cancer

Question 18

Alternative splicing in eukaryotes allows for which of the following?

Accepted Answer

The production of multiple protein variants from a single gene

Question 19

Which of the following statements about the leader sequence in the trp operon is correct?

Accepted Answer

It is involved in attenuation, forming different stem-loop structures depending on tryptophan levels.

Regulation of Gene Expression: Operons and Eukaryotic Control

Study Guide - Practice Questions