Question 1

Which of the following best describes the regulation of the trp operon in Escherichia coli when tryptophan is abundant?

Accepted Answer

The repressor binds to the operator, blocking RNA polymerase and preventing transcription.

Question 2

What would be the phenotype of an E. coli cell with a mutation in the trp promoter that prevents RNA polymerase binding?

Accepted Answer

The cell would be unable to synthesize tryptophan.

Question 3

Which molecule acts as the inducer for the lac operon in E. coli?

Accepted Answer

Allolactose

Question 4

How does glucose inhibit the transcription of the lac operon in E. coli?

Accepted Answer

By preventing the formation of cAMP, which is required for CRP activation.

Question 5

Which of the following is TRUE regarding two-component regulatory systems in bacteria?

Accepted Answer

They involve a sensor kinase and a response regulator.

Question 6

What triggers the stringent response in bacterial cells?

Accepted Answer

Scarcity of amino acids, leading to uncharged tRNAs in the ribosome

Question 7

Which modified nucleotide acts as the intracellular messenger during the stringent response?

Accepted Answer

ppGpp

Question 8

Which of the following best explains why attenuation of transcription cannot occur in eukaryotes?

Accepted Answer

Transcription and translation are spatially separated in eukaryotes.

Question 9

What would be the effect on β-galactosidase activity in E. coli if the operator mutated so that LacI could not bind?

Accepted Answer

β-galactosidase would be constitutively produced, regardless of lactose presence.

Question 10

Which of the following is a key difference between riboswitch regulation and regulation by repressors or activators?

Accepted Answer

Riboswitches regulate gene expression by binding small molecules directly to mRNA.

Question 11

In the context of quorum sensing in Staphylococcus aureus, what is the role of AIP (autoinducing peptide)?

Accepted Answer

It binds to a sensor kinase, triggering phosphorylation of a response regulator that activates transcription of virulence genes.

Question 12

Which sigma factor in E. coli is primarily responsible for the transcription of heat-shock genes?

Accepted Answer

$$\$$sigma^{32}$$

Question 13

What would be the effect on tryptophan synthesis in E. coli if the trp repressor could not bind tryptophan?

Accepted Answer

The trp operon would be constitutively expressed, regardless of tryptophan levels.

Question 14

Which of the following best describes the role of alternative sigma factors in bacterial gene regulation?

Accepted Answer

They allow RNA polymerase to recognize different promoter sequences under specific conditions.

Question 15

Which of the following is a direct effect of the stringent response in bacteria?

Accepted Answer

Decreased rRNA and tRNA synthesis

Question 16

What is the function of the CAP (CRP) protein in the regulation of the lac operon?

Accepted Answer

It binds to the promoter in the presence of cAMP, enhancing RNA polymerase binding.

Question 17

Which of the following scenarios would result in maximal transcription of the lac operon?

Accepted Answer

Low glucose, high lactose

Question 18

Which of the following is NOT a mechanism of post-transcriptional regulation in bacteria?

Accepted Answer

Alternative sigma factor usage

Question 19

What would be the effect on β-galactosidase activity in E. coli if adenylyl cyclase activity was constitutive?

Accepted Answer

β-galactosidase would be produced at high levels even in the presence of glucose.

Microbial Regulation of Gene Expression: Mechanisms and Examples Ch 7

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