$$\mathrm{DNA} \xrightarrow{\text{RNA\ polymerase}} \mathrm{mRNA}$$

$$\mathrm{mRNA} \xrightarrow{\text{ribosome}} \mathrm{Protein}$$

Question 1

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

Accepted Answer

A set of genes transcribed into a single polycistronic mRNA under the control of a single promoter and operator.

Question 2

In the lac operon, what is the role of allolactose?

Accepted Answer

It serves as an inducer, binding to the repressor and inactivating it to allow transcription.

Question 3

Which equation correctly represents the process of transcription in bacteria?

Accepted Answer

$$\mathrm{DNA} \xrightarrow{	ext{RNA\ polymerase}} \mathrm{mRNA}$$

Question 4

A bacterium is growing in a medium containing both glucose and lactose. Which regulatory phenomenon ensures that glucose is used first?

Accepted Answer

Metabolite repression (catabolite repression)

Question 5

Which of the following statements about negative control of gene expression is correct?

Accepted Answer

A repressor protein binds to the operator to block RNA polymerase from transcribing the genes.

Question 6

Which molecule acts as an allosteric activator for the cAMP receptor protein (CRP) in the lac operon?

Accepted Answer

cAMP (cyclic AMP)

Question 7

A mutation disables the sensor kinase in a two-component regulatory system. What is the most likely consequence?

Accepted Answer

The cell will be unable to detect environmental signals and properly regulate gene expression.

Question 8

Which of the following best describes a regulon?

Accepted Answer

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

Question 9

During sporulation in Bacillus subtilis, which event triggers the cascade of gene expression changes?

Accepted Answer

Phosphorylation of the sporulation factor Spo0A.

Question 10

Which of the following is a real-world example of quorum sensing leading to increased virulence in bacteria?

Accepted Answer

E. coli O157:H7 produces Al-3, which, together with host stress hormones, activates toxin production.

Question 11

Which of the following equations correctly represents the process of translation?

Accepted Answer

$$\mathrm{mRNA} \xrightarrow{	ext{ribosome}} \mathrm{Protein}$$

Question 12

Which of the following is NOT a mechanism by which activator proteins enhance transcription?

Accepted Answer

Blocking the operator to prevent RNA polymerase binding.

Question 13

A bacterial cell is exposed to excess arginine. What regulatory mechanism will be activated?

Accepted Answer

Repression of arginine biosynthetic enzymes via a co-repressor mechanism.

Question 14

Which of the following statements about sigma factors is correct?

Accepted Answer

Alternative sigma factors allow bacteria to express different sets of genes in response to environmental changes.

Question 15

Which of the following best explains diauxic growth in bacteria?

Accepted Answer

Sequential utilization of two carbon sources, with a lag phase between them due to catabolite repression.

Question 16

Which of the following is a multi-step regulatory process involving both positive and negative control in the lac operon?

Accepted Answer

Lactose binds to the repressor, inactivating it, while cAMP-CRP complex binds to the activator site to recruit RNA polymerase.

Question 17

Which of the following is a correct sequence of events in a two-component regulatory system?

Accepted Answer

Sensor kinase detects signal, phosphorylates itself, transfers phosphate to response regulator, which then regulates gene expression.

Question 18

Which of the following is a plausible consequence of a mutation that prevents cAMP synthesis in E. coli?

Accepted Answer

The lac operon will not be activated efficiently when glucose is absent.

Question 19

Which of the following is a real-life application of posttranslational modification in bacteria?

Accepted Answer

Rapid activation or inactivation of enzymes in response to environmental changes.

Microbial Regulatory Systems: Gene Expression and Control in Bacteria

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