Question 1

Which of the following best describes a regulon in bacterial gene regulation?

Accepted Answer

A set of genes and operons scattered around the chromosome with related functions, coordinately controlled by a single repressor or activator protein.

Question 2

What is the primary role of sigma factors in bacterial transcription?

Accepted Answer

Sigma factors direct RNA polymerase to specific promoter sequences, enabling the transcription of particular sets of genes.

Question 3

How do anti-sigma factors regulate sigma factor activity?

Accepted Answer

By binding directly to specific sigma factors and blocking their access to RNA polymerase.

Question 4

Which mechanism allows riboswitches to regulate gene expression at the level of transcription?

Accepted Answer

Ligand binding stabilizes a secondary structure that forms a transcription termination stem, causing transcription to terminate before the coding sequence is transcribed.

Question 5

Which class of small regulatory RNA (sRNA) molecules is encoded by intergenic sequences and typically 100–200 nucleotides in length?

Accepted Answer

Small RNA (sRNA)

Question 6

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

Accepted Answer

It interacts with RNA polymerase at the promoter to increase the rate of transcription initiation.

Question 7

During diauxic growth, what happens to the expression of the lac operon when glucose is present along with lactose?

Accepted Answer

Expression of the lac operon is repressed due to catabolite repression by glucose.

Question 8

Which of the following is a real-world example of quorum sensing in bacteria?

Accepted Answer

The regulation of bioluminescence in Vibrio fischeri colonizing the Hawaiian squid.

Question 9

What triggers the burst of luminescence in Vibrio fischeri during quorum sensing?

Accepted Answer

Accumulation of autoinducer above a threshold level, which binds to LuxR and activates luciferase gene transcription.

Question 10

Which process allows Streptococcus to become competent for natural transformation?

Accepted Answer

Accumulation of competence stimulation peptide (CSP) triggers a phosphorylation cascade that activates ComX, an alternative sigma factor.

Question 11

How does phase variation in Salmonella enterica help the bacterium evade the host immune system?

Accepted Answer

By randomly inverting a promoter region, Salmonella alternates between expressing two different flagellin proteins, allowing it to switch antigenic states.

Question 12

Which of the following mechanisms is used by Neisseria gonorrhoeae to achieve phase variation of outer membrane proteins?

Accepted Answer

Slipped-strand mispairing during DNA replication, which alters the translational reading frame.

Question 13

Which equation correctly represents the conversion of ATP to cyclic AMP (cAMP) by adenylate cyclase?

Accepted Answer

$$\mathrm{ATP} \xrightarrow{	ext{adenylate cyclase}} \mathrm{cAMP} + \mathrm{PP_i}$$

Question 14

Which sRNA molecule regulates oxidative stress gene expression in E. coli by inhibiting translation?

Accepted Answer

OxyS

Question 15

What is the effect of a riboswitch that sequesters the ribosome-binding site upon ligand binding?

Accepted Answer

Translation is blocked because the ribosome cannot bind to the mRNA.

Question 16

Which of the following is NOT a function of regulatory sRNAs?

Accepted Answer

Stimulating protein synthesis by binding to ribosomes

Question 17

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

Accepted Answer

Allolactose binds to the LacI repressor, reducing its affinity for the operator and allowing transcription of lacZYA.

Question 18

Which of the following statements about second messengers is correct?

Accepted Answer

Second messengers are small molecules that regulate the activities of regulatory proteins and RNAs, often in response to environmental changes.

Question 19

Which of the following best explains why small RNAs (sRNAs) are considered an economical way to regulate gene expression?

Accepted Answer

They diffuse rapidly and act on preexisting messages without requiring protein synthesis.

Gene Regulation in Bacteria: Sigma Factors, Regulatory RNAs, Second Messengers, and Quorum Sensing

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