Question 1

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

Accepted Answer

It enables E. coli to metabolize lactose only when lactose is present.

Question 2

What is the role of the lac repressor in the regulation of the lac operon?

Accepted Answer

It binds to the operator and blocks RNA polymerase when lactose is absent.

Question 3

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

Accepted Answer

β-galactosidase

Question 4

If a mutation prevents the lac repressor from binding to the operator, what would be the most likely outcome?

Accepted Answer

The lac operon would be continuously expressed, even when lactose is absent.

Question 5

Which of the following statements about gene expression in prokaryotes is correct?

Accepted Answer

Gene expression can be regulated in response to environmental conditions.

Question 6

The trp operon is an example of a repressible operon. What does this mean?

Accepted Answer

Transcription is repressed by the presence of tryptophan.

Question 7

Which of the following best explains why E. coli silences genes responsible for amino acid production when those amino acids are available in the environment?

Accepted Answer

To conserve energy and resources.

Question 8

What would happen to the trp operon if tryptophan levels in the environment suddenly dropped to zero?

Accepted Answer

The trp repressor would be inactive, allowing transcription of the trp operon.

Question 9

Which of the following is a key difference between inducible and repressible operons?

Accepted Answer

Inducible operons are activated by the presence of a substrate, while repressible operons are repressed by the presence of an end product.

Question 10

A researcher adds lactose to a culture of E. coli. Which of the following events is most likely to occur?

Accepted Answer

The lac repressor is inactivated, allowing transcription of the lac operon.

Question 11

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

Accepted Answer

It is the DNA sequence where a repressor protein can bind to regulate transcription.

Question 12

In the lac operon, which gene product allows lactose to enter the cell?

Accepted Answer

Permease

Question 13

Which of the following equations best represents the hydrolysis of lactose by β-galactosidase?

Accepted Answer

$$\mathrm{Lactose} + \mathrm{H}_2\mathrm{O} \rightarrow \mathrm{Glucose} + \mathrm{Galactose}$$

Question 14

A mutation causes the trp repressor to remain active even in the absence of tryptophan. What is the most likely effect on the cell?

Accepted Answer

The cell will be unable to produce tryptophan, even when it is needed.

Question 15

Which of the following scenarios best illustrates environmental control of gene expression in E. coli?

Accepted Answer

E. coli expresses genes for lactose metabolism only when lactose is present.

Question 16

Which of the following is true about the structure of an operon?

Accepted Answer

It contains multiple genes controlled by a single promoter.

Question 17

Which of the following is a real-world consequence of improper regulation of the lac operon in E. coli?

Accepted Answer

E. coli would waste energy expressing unnecessary enzymes when lactose is absent.

Question 18

Which of the following best describes an allosteric protein in the context of operon regulation?

Accepted Answer

A protein that changes its conformation upon binding a small molecule, affecting its ability to bind DNA.

Question 19

Which of the following is the correct sequence of events when lactose becomes available to E. coli?

Accepted Answer

Lactose binds to the lac repressor, inactivating it; RNA polymerase transcribes the lac operon; enzymes for lactose metabolism are produced.

Regulation of Gene Expression: Prokaryotic Operons

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