Question 1

Which of the following best describes the function of a repressor protein in negative control of gene expression in bacteria?

Accepted Answer

It binds to the operator region and blocks RNA polymerase from transcribing the genes.

Question 2

A mutation in the gene encoding the maltose activator protein prevents it from binding maltose. What is the most likely consequence for the maltose operon in E. coli?

Accepted Answer

The operon will not be transcribed even in the presence of maltose.

Question 3

Which structural motif is commonly found in DNA-binding proteins and is characterized by two α-helices connected by a short turn?

Accepted Answer

Helix-turn-helix

Question 4

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

Accepted Answer

It acts as an inducer by binding to the repressor and inactivating it.

Question 5

Which of the following best explains why attenuation does not occur in eukaryotes?

Accepted Answer

Transcription and translation are separated by organelles in eukaryotes.

Question 6

A bacterium is exposed to high levels of tryptophan. What is the expected effect on the trp operon?

Accepted Answer

Transcription of the trp operon will be repressed due to corepressor binding.

Question 7

Which of the following is a correct description of a regulon?

Accepted Answer

A group of operons controlled by the same regulatory protein.

Question 8

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

Accepted Answer

They regulate gene expression by base pairing with mRNA.

Question 9

Which of the following best describes the mechanism of feedback inhibition?

Accepted Answer

The end product of a pathway binds to the first enzyme, inhibiting its activity.

Question 10

A two-component regulatory system in bacteria typically consists of which two elements?

Accepted Answer

A sensor kinase and a response regulator

Question 11

During chemotaxis, what is the effect of CheY-P on flagellar rotation?

Accepted Answer

It causes clockwise rotation and tumbling.

Question 12

Which of the following statements about quorum sensing is correct?

Accepted Answer

It allows bacteria to assess their population density and coordinate gene expression.

Question 13

Which of the following is a feature of a riboswitch?

Accepted Answer

It is an mRNA region that binds small metabolites to regulate gene expression.

Question 14

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 consumes glucose first, then after a lag phase, switches to lactose metabolism.

Question 15

Which of the following equations best 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 16

A mutation causes the operator region of the lac operon to be deleted. What is the most likely outcome?

Accepted Answer

The lac operon will be constitutively expressed.

Question 17

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

Accepted Answer

Synthesis of macromolecules is shut down and stress survival pathways are activated.

Question 18

Which of the following best describes the function of an allosteric enzyme in feedback inhibition?

Accepted Answer

It has both an active site for substrate binding and an allosteric site for end product binding.

Question 19

Which of the following is a plausible effect of a mutation that prevents the formation of the stem-loop structure in the leader sequence of the trp operon?

Accepted Answer

Transcription of the trp operon will proceed even when tryptophan is abundant.

Question 20

Which of the following best describes the role of covalent modification in post-translational regulation?

Accepted Answer

It can reversibly activate or inactivate enzymes by adding or removing chemical groups.

Microbial Regulatory Systems: Mechanisms of Gene Expression and Regulation

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