Q: Which of the following equations best represents the energy cost of transcription and translation for the lac operon?

$$ \text{Total Energy Cost} = n_{\text{mRNA}} \times E_{\text{transcription}} + n_{\text{protein}} \times E_{\text{translation}} $$

Question 1

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

Accepted Answer

It encodes enzymes that metabolize lactose for energy.

Question 2

The lac operon is an example of which type of gene regulation in prokaryotes?

Accepted Answer

Negative inducible regulation

Question 3

Which gene encodes the repressor protein that binds to the operator of the lac operon?

Accepted Answer

lacI

Question 4

In the absence of lactose, what happens to the lac operon in E. coli?

Accepted Answer

The repressor binds to the operator, blocking transcription.

Question 5

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

Accepted Answer

It acts as an inducer by binding to the repressor and inactivating it.

Question 6

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

Accepted Answer

The lac operon will be transcribed continuously, regardless of lactose presence.

Question 7

Which of the following correctly matches the lac operon gene with its product?

Accepted Answer

lacA: transacetylase

Question 8

A researcher adds lactose to a culture of E. coli. Which of the following best describes the sequence of molecular events that follows?

Accepted Answer

Lactose binds to the repressor, causing it to release from the operator, and RNA polymerase transcribes the operon.

Question 9

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

Accepted Answer

It is only transcribed when an inducer (lactose) is present.

Question 10

Suppose a mutation causes the lac repressor to lose its ability to bind lactose. What would be the effect on the lac operon when lactose is present?

Accepted Answer

The operon would not be transcribed because the repressor would remain bound to the operator.

Question 11

Which of the following equations best represents the energy cost of transcription and translation for the lac operon?

Accepted Answer

$$ 	ext{Total Energy Cost} = n_{	ext{mRNA}} 	imes E_{	ext{transcription}} + n_{	ext{protein}} 	imes E_{	ext{translation}} $$

Question 12

In a scenario where both glucose and lactose are present, what is the expected activity of the lac operon?

Accepted Answer

The lac operon is repressed due to catabolite repression by glucose.

Question 13

Which of the following best describes the structure of the lac operon?

Accepted Answer

It consists of a promoter, operator, and three structural genes.

Question 14

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

Accepted Answer

The operon will be transcribed regardless of lactose presence.

Question 15

Which of the following is NOT a function of the lac repressor protein?

Accepted Answer

Binding to the promoter to initiate transcription

Question 16

If E. coli is grown in the presence of lactose but absence of glucose, what is the expected outcome for the lac operon?

Accepted Answer

The lac operon will be highly transcribed.

Question 17

Which of the following best explains why the lac operon is not transcribed in the absence of lactose?

Accepted Answer

The repressor binds to the operator, blocking RNA polymerase.

Question 18

Which of the following statements about the lac operon is correct?

Accepted Answer

The lac operon is transcribed only when lactose is present and glucose is absent.

Question 19

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

Accepted Answer

It is the site where the repressor binds to block transcription.

Question 20

A medical researcher is studying a strain of E. coli that cannot metabolize lactose even when lactose is present. Which mutation could explain this phenotype?

Accepted Answer

A mutation in the lacZ gene preventing production of beta-galactosidase.

Gene Regulation: The Lac Operon in Prokaryotes

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