Question 1

Which of the following best describes the difference between negative and positive control of transcription in bacteria?

Accepted Answer

Negative control involves repressor proteins preventing transcription, while positive control involves activator proteins enhancing transcription.

Question 2

A mutation in the operator region of the lac operon prevents the lac repressor from binding. What is the most likely outcome?

Accepted Answer

The lac operon will be constitutively expressed, regardless of lactose presence.

Question 3

Which of the following is the correct sequence of events for induction of the lac operon in E. coli when lactose is present and glucose is absent?

Accepted Answer

Allolactose binds the repressor, repressor dissociates from operator, CAP-cAMP binds promoter, RNA polymerase transcribes operon.

Question 4

Which enzyme is responsible for cleaving lactose into glucose and galactose in the lac operon system?

Accepted Answer

β-galactosidase

Question 5

What is the role of the CAP-cAMP complex in the regulation of the lac operon?

Accepted Answer

It bends DNA to increase RNA polymerase efficiency at the promoter.

Question 6

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

Accepted Answer

It is turned off when the end-product, tryptophan, is abundant.

Question 7

A mutation in the trpL region that prevents the formation of the 3-4 stem-loop structure would most likely result in:

Accepted Answer

Constitutive expression of the trp operon, even when tryptophan is present.

Question 8

Which structural motif is most commonly found in bacterial regulatory proteins that bind DNA?

Accepted Answer

Helix-turn-helix (HTH)

Question 9

In the context of the lac operon, what is the effect of glucose on cAMP levels and operon expression?

Accepted Answer

Glucose inhibits cAMP production, reducing lac operon expression.

Question 10

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

Accepted Answer

Glucose absent, lactose present

Question 11

Which of the following mechanisms is NOT a form of translational regulation in bacteria?

Accepted Answer

Feedback inhibition of enzyme activity

Question 12

A mutation in the allosteric domain of the lac repressor protein that prevents inducer binding would result in:

Accepted Answer

Permanent repression of the lac operon, even in the presence of lactose

Question 13

Which of the following best describes attenuation in the trp operon?

Accepted Answer

A mechanism that allows fine-tuning of transcription based on tryptophan levels

Question 14

Which of the following equations best represents the relationship between enzyme activity and gene regulation in a constitutively expressed gene?

Accepted Answer

$$E_{activity} = k_{cat} 	imes [E]_{total}$$

Question 15

Which of the following is a real-world example of feedback inhibition in bacterial gene regulation?

Accepted Answer

Tryptophan acting as a co-repressor to inhibit its own synthesis in the trp operon

Question 16

Which of the following statements about operons is FALSE?

Accepted Answer

Operons are common in eukaryotic genomes.

Question 17

Which of the following would most likely result from a base-substitution mutation that disrupts the symmetry of the inverted repeat in the lac operator?

Accepted Answer

The lac repressor cannot bind, leading to constitutive expression of the operon.

Question 18

Which of the following best describes the function of the Shine-Dalgarno sequence in bacterial gene expression?

Accepted Answer

It is the ribosome binding site on mRNA for translation initiation.

Question 19

Which of the following is a likely consequence of a mutation that prevents the formation of the 2-3 stem loop in the trp operon leader region?

Accepted Answer

Transcription will terminate prematurely, even when tryptophan is absent.

Gene Expression and Regulation in Bacteria: Mechanisms and Operon Models

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