$$\text{Aporepressor} + \text{Co-repressor} \rightarrow \text{Functional Repressor}$$

Question 1

Which of the following best describes negative regulation in gene expression?

Accepted Answer

A repressor protein binds to DNA and prevents transcription unless inactivated by an inducer.

Question 2

In the lac operon, what is the role of allolactose?

Accepted Answer

It is an inducer that inactivates the repressor, allowing transcription.

Question 3

Which scenario best illustrates positive regulation of gene expression?

Accepted Answer

A transcriptional activator protein binds to the activator binding site, increasing transcription.

Question 4

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

Accepted Answer

A hairpin structure forms in the mRNA, causing attenuation and terminating transcription.

Question 5

Which of the following statements about attenuation is correct?

Accepted Answer

Attenuation uses translation to control transcription by forming secondary structures in mRNA.

Question 6

A gene in enteric bacteria encodes both a dehydrogenase and binds its own operator to control its expression. This is an example of:

Accepted Answer

Autoregulation

Question 7

Which of the following best describes the function of a riboswitch?

Accepted Answer

An RNA element that changes conformation in response to a metabolite, affecting gene expression.

Question 8

In negative regulation of an inducible operon, what is the effect of the inducer?

Accepted Answer

The inducer inactivates the repressor, reducing its DNA binding and allowing transcription.

Question 9

Which equation best represents the formation of a functional repressor in a repressible operon?

Accepted Answer

$$	ext{Aporepressor} + 	ext{Co-repressor} ightarrow 	ext{Functional Repressor}$$

Question 10

Which of the following is true regarding the 'on/off' state of an operon?

Accepted Answer

'Off' does not mean complete absence of mRNA; occasional transcription can occur due to random events.

Question 11

A mutation causes the repressor protein of the lac operon to lose its ability to bind allolactose. What is the most likely outcome?

Accepted Answer

The operon will remain repressed even in the presence of lactose.

Question 12

Which of the following is a real-world example of autoregulation?

Accepted Answer

Cell cycle regulation where a protein regulates its own expression.

Question 13

Which statement about prokaryotic regulation of translation is correct?

Accepted Answer

Translation can be regulated by RNA elements such as riboswitches.

Question 14

If a co-repressor is a metabolic product, what is the likely effect on the operon it regulates?

Accepted Answer

The operon will be repressed when the product is present.

Question 15

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

Accepted Answer

It is the DNA sequence where regulatory proteins such as repressors bind to control transcription.

Question 16

Which scenario would most likely result in the lac operon being 'stuck off'?

Accepted Answer

A mutation in the promoter prevents RNA polymerase binding.

Question 17

Which of the following is a plausible outcome if the trp operon repressor cannot bind tryptophan?

Accepted Answer

The operon will be constitutively expressed even when tryptophan is abundant.

Question 18

Which sequence is most likely to be involved in riboswitch-mediated regulation of Met/Cys synthesis?

Accepted Answer

5-box sequence

Question 19

A cell has a mutation that prevents the formation of a hairpin structure in the trp operon leader sequence. What is the most likely effect?

Accepted Answer

Transcription will proceed even when tryptophan is abundant.

Prokaryotic Gene Regulation: Mechanisms and Examples

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