Question 1

Which of the following best describes the role of the sigma ($$\sigma) $$factor in bacterial transcription?

Accepted Answer

It guides RNA polymerase to the promoter to initiate transcription.

Question 2

In the lac operon, what is the effect of allolactose binding to the LacI repressor?

Accepted Answer

It causes LacI to dissociate from the operator, allowing transcription.

Question 3

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

Accepted Answer

Low glucose, high lactose

Question 4

What is the primary function of the two-component signal transduction system in bacteria?

Accepted Answer

To sense environmental signals and alter gene expression via phosphorylation cascades.

Question 5

Which molecule acts as the inducer in the lac operon system?

Accepted Answer

Allolactose

Question 6

How does catabolite repression affect the lac operon when glucose is present?

Accepted Answer

It decreases cAMP levels, inactivating CRP and reducing lac operon transcription.

Question 7

Which of the following best explains the phenomenon of diauxic growth in E. coli when both glucose and lactose are present?

Accepted Answer

E. coli first utilizes glucose, then switches to lactose after glucose is depleted.

Question 8

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

Accepted Answer

It acts as an activator, enhancing RNA polymerase binding to the promoter.

Question 9

In the trp operon, what happens when tryptophan levels are high?

Accepted Answer

The trp repressor binds tryptophan, forming a holorepressor that binds the operator and blocks transcription.

Question 10

Which of the following is a key feature of attenuation in the trp operon?

Accepted Answer

It relies on the formation of alternative stem-loop structures in the leader mRNA.

Question 11

Which regulatory mechanism allows bacteria to rapidly switch the type of flagellin protein produced?

Accepted Answer

Phase variation via DNA inversion

Question 12

What is the function of small regulatory RNAs (sRNAs) in bacteria?

Accepted Answer

They base-pair with mRNA to regulate translation, often preventing it.

Question 13

Which of the following best describes the stringent response in bacteria?

Accepted Answer

It is triggered by nutrient limitation and leads to the production of ppGpp, reducing rRNA synthesis.

Question 14

How does cyclic di-GMP ($$c-di-$$GMP) influence bacterial biofilm formation?

Accepted Answer

It activates genes for biofilm formation and represses flagellar genes.

Question 15

Which autoinducer is commonly used in quorum sensing by Vibrio fischeri to regulate bioluminescence?

Accepted Answer

Homoserine lactone

Question 16

What is the effect of anti-sigma factors in bacterial cells?

Accepted Answer

They inhibit sigma factor activity until needed.

Question 17

Which of the following best explains how riboswitches regulate gene expression?

Accepted Answer

They bind small molecules to alter mRNA structure, affecting transcription or translation.

Question 18

A mutation in the gene encoding the sensor kinase of a two-component system would most likely result in which of the following?

Accepted Answer

Impaired ability to sense environmental signals and alter gene expression.

Question 19

Which of the following is a direct consequence of high glucose levels in E. coli?

Accepted Answer

Decreased cAMP levels and inactivation of CRP.

Question 20

Which of the following best describes the function of the AraC protein in the arabinose operon?

Accepted Answer

It acts as a repressor in the absence of arabinose and as an activator in its presence.

Molecular Regulation of Gene Expression in Microbes

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