Question 1

Which of the following best describes the function of the operator region in a prokaryotic operon?

Accepted Answer

It is the DNA sequence where the repressor protein binds to regulate transcription of adjacent genes.

Question 2

In the lac operon, what is the direct effect of lactose binding to the repressor protein?

Accepted Answer

It causes the repressor to detach from the operator, allowing transcription to proceed.

Question 3

Which enzyme is responsible for cleaving lactose into glucose and galactose in E. coli?

Accepted Answer

β-galactosidase

Question 4

A mutation in the lacI gene that prevents the repressor from binding lactose will result in which phenotype?

Accepted Answer

No transcription of the lac operon even when lactose is present

Question 5

Which of the following best explains why the lac operon is considered an inducible system?

Accepted Answer

The operon is transcribed only when a specific substrate (lactose) is present.

Question 6

Which of the following conditions will result in the highest level of lac operon expression in E. coli?

Accepted Answer

Lactose present, glucose absent

Question 7

What is the role of cyclic AMP (cAMP) in the regulation of the lac operon?

Accepted Answer

cAMP binds to CAP, allowing the CAP-cAMP complex to stimulate RNA polymerase binding to the promoter.

Question 8

Which of the following equations correctly represents the reaction catalyzed by β-galactosidase?

Accepted Answer

$$\mathrm{Lactose} + \mathrm{H}_2\mathrm{O} \xrightarrow{\beta	ext{-galactosidase}} \mathrm{Glucose} + \mathrm{Galactose}$$

Question 9

A mutation in the operator region (O^c) of the lac operon that prevents repressor binding will result in which phenotype?

Accepted Answer

Constitutive expression of the lac operon regardless of lactose presence

Question 10

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

Accepted Answer

A mechanism where transcription is greatly reduced but not completely prevented, depending on tryptophan availability.

Question 11

In the trp operon, what is the role of tryptophan?

Accepted Answer

It acts as a corepressor, enabling the repressor to bind the operator and block transcription.

Question 12

Which of the following statements about polycistronic mRNA is correct?

Accepted Answer

It is an mRNA that encodes multiple proteins, each translated from a different region of the same transcript.

Question 13

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

Accepted Answer

The operon is transcribed unless tryptophan is present to act as a corepressor.

Question 14

A partial diploid E. coli strain has the genotype $$I^+O^cZ^+/F^+O^+Z^+. $$What will be the phenotype regarding β-galactosidase activity in the absence of lactose?

Accepted Answer

Constitutive β-galactosidase activity

Question 15

Which of the following scenarios would result in the formation of the antiterminator hairpin in the trp operon leader sequence?

Accepted Answer

Low levels of tryptophan, ribosome stalls at trp codons

Question 16

Which of the following best describes negative control of gene expression?

Accepted Answer

Gene expression occurs unless it is shut off by a regulator molecule.

Question 17

Which of the following is a real-world application of understanding the lac operon system?

Accepted Answer

Designing antibiotics that target bacterial gene regulation.

Question 18

Which of the following is true regarding the CAP-cAMP complex in the lac operon?

Accepted Answer

It binds to the promoter region to enhance RNA polymerase binding when glucose is absent.

Question 19

Which of the following best explains why the presence of glucose inhibits lac operon expression even if lactose is present?

Accepted Answer

Glucose decreases cAMP levels, so CAP cannot bind and stimulate transcription.

CH16: Regulation of Gene Expression in Prokaryotes: The lac and trp Operons

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