Quiz: Gene Regulation in Bacteria — 10 perguntas

1. What is a repressor protein in gene regulation mechanisms?

A. A molecule that enhances RNA polymerase binding to the promoter

B. A molecule that binds to the promoter to activate gene expression

C. A protein that binds to the operator to prevent transcription

D. A DNA sequence where RNA polymerase initiates transcription

Answer: (C)

Explicação

A repressor protein is a regulatory molecule that binds to the operator region of an operon to block transcription, thereby turning gene expression OFF in gene regulation mechanisms.

2. What is the primary function of the repressor protein in the lac operon?

A. To enhance RNA polymerase binding to the promoter

B. To prevent transcription by binding to the operator

C. To activate structural genes directly

D. To produce lactose enzymes

Answer: (B)

Explicação

The repressor binds to the operator to block RNA polymerase from transcribing structural genes. It does not enhance binding or activate genes directly.

3. What is the name of the gene that encodes the repressor protein in the lac operon?

A. lacI

B. lacY

C. lacA

D. lacZ

Answer: (A)

Explicação

The gene that encodes the repressor protein in the lac operon is called 'lacI', as explicitly stated in the content. The other options are structural genes of the lac operon, not the repressor gene.

4. In the lac operon, what molecule acts as an inducer when lactose is present?

A. Lactose itself

B. Allolactose

C. Glucose

D. cAMP

Answer: (B)

Explicação

Allolactose, a derivative of lactose, binds to the repressor, causing it to release from the operator, thereby inducing transcription.

5. What is the primary role of the promoter and operator in the lac operon?

A. The promoter is where RNA polymerase binds to start transcription.

B. The operator initiates transcription by binding RNA polymerase.

C. The promoter binds repressor proteins to block transcription.

D. The operator encodes structural proteins for lactose metabolism.

Answer: (A)

Explicação

The promoter's main role is to serve as the binding site for RNA polymerase, enabling the initiation of transcription. The operator's role is to be the site where repressor proteins bind to regulate the transcription process. Therefore, the correct answer is that the promoter is where RNA polymerase binds to start transcription.

6. Which of the following correctly describes the negative inducible system in the lac operon?

A. The operon is always ON unless repressed

B. The operon is OFF by default and turns ON in presence of an inducer

C. The operon is permanently turned OFF

D. The system only works in the absence of lactose

Answer: (B)

Explicação

This system is normally OFF due to repressor binding; lactose (through allolactose) inactivates the repressor, turning transcription ON.

7. Which gene encodes the repressor protein in the lac operon?

A. lacZ

B. lacY

C. lacA

D. lacI

Answer: (D)

Explicação

The lacI gene encodes the repressor protein that can bind to the operator to block transcription.

8. What is the role of the promoter in the operon structure?

A. To bind repressor proteins

B. To initiate transcription by RNA polymerase

C. To block access to the operator

D. To code for structural proteins

Answer: (B)

Explicação

The promoter is the DNA sequence where RNA polymerase binds to start transcription of the operon’s genes.

9. Which structural genes are involved in lactose metabolism in the lac operon?

A. lacA, lacY, lacZ

B. lacI, lacP, lacO

C. lacM, lacN, lacR

D. lacS, lacK, lacQ

Answer: (A)

Explicação

The lacZ, lacY, and lacA genes code for enzymes involved in lactose breakdown, and are part of the structural genes in the operon.

10. Why does bacterial gene regulation via operons like lac operon conserve energy?

A. It prevents the unnecessary production of enzymes when lactose is absent

B. It speeds up all gene expression regardless of environmental conditions

C. It permanently activates all structural genes

D. It only regulates genes related to glucose metabolism

Answer: (A)

Explicação

By only producing lactose-digesting enzymes when lactose is present, bacteria avoid wasteful energy expenditure, demonstrating efficient regulation.