Question 1

Which of the following best describes the function of an operon in bacterial gene regulation?

Accepted Answer

A cluster of genes transcribed into a single polycistronic mRNA under the control of a single promoter.

Question 2

In the context of negative control of gene expression, what is the role of an effector molecule?

Accepted Answer

It binds to the repressor protein, altering its conformation and affecting its ability to bind DNA.

Question 3

Which scenario would most likely result in the induction of the lac operon in E. coli?

Accepted Answer

No glucose, lactose present.

Question 4

What is the primary mechanism by which catabolite repression ensures preferential use of glucose over other sugars in bacteria?

Accepted Answer

By lowering cyclic AMP levels, which prevents activation of catabolic operons for other sugars.

Question 5

Which of the following best explains why the addition of arginine to a bacterial culture represses the synthesis of arginine biosynthetic enzymes?

Accepted Answer

Arginine acts as a co-repressor, activating the repressor protein to bind the operator and block transcription.

Question 6

A mutation in the gene encoding the cyclic AMP receptor protein (CRP) would most likely result in which phenotype in E. coli?

Accepted Answer

Reduced expression of catabolic operons when glucose is absent.

Question 7

Which of the following statements about two-component regulatory systems is correct?

Accepted Answer

They use a sensor kinase to detect environmental signals and a response regulator to control gene expression.

Question 8

In quorum sensing, what is the role of autoinducer molecules such as acyl homoserine lactones (AHLs)?

Accepted Answer

They diffuse across cell membranes and, at high concentrations, activate transcription of specific genes.

Question 9

Which of the following best describes the function of alternative sigma factors in bacteria?

Accepted Answer

They allow RNA polymerase to recognize different promoter sequences, enabling global regulation of gene families.

Question 10

A bacterium is exposed to both glucose and lactose. Which of the following best describes the expected pattern of lac operon expression?

Accepted Answer

The lac operon will be repressed until glucose is depleted, then induced.

Question 11

Which of the following equations correctly represents the phosphorylation event in a two-component regulatory system?

Accepted Answer

$$\mathrm{Sensor\ kinase} + \mathrm{ATP} \rightarrow \mathrm{Sensor\ kinase{-}P} + \mathrm{ADP}$$

Question 12

Which of the following is a direct consequence of the binding of an inducer molecule to a repressor protein in the lac operon?

Accepted Answer

The repressor changes conformation and cannot bind the operator, allowing transcription.

Question 13

Which of the following best explains why the maltose operon requires an activator protein for transcription?

Accepted Answer

The promoter weakly binds RNA polymerase and requires the activator to facilitate binding.

Question 14

Which of the following is an example of a regulon?

Accepted Answer

Multiple operons scattered across the chromosome, all controlled by the same regulatory protein.

Question 15

During sporulation in Bacillus subtilis, which event triggers the activation of the sigma factor $$\sigma^F$$?

Accepted Answer

Phosphorylation of Spo0A in response to adverse conditions.

Question 16

Which of the following best describes the effect of quorum sensing on virulence factor production in pathogenic E. coli?

Accepted Answer

Quorum sensing activates transcriptional regulators that induce toxin production when cell density and host signals are high.

Question 17

Which of the following statements about polycistronic mRNA is correct?

Accepted Answer

It is transcribed from an operon and encodes multiple proteins.

Question 18

Which of the following best explains the lag phase observed in diauxic growth when E. coli switches from glucose to lactose metabolism?

Accepted Answer

The cell is synthesizing the enzymes required for lactose metabolism after glucose is depleted.

Microbial Regulatory Systems: Mechanisms of Gene Expression Control in Bacteria

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