Q: Which of the following equations correctly represents the relationship between glucose, cAMP, and CRP activity in the lac operon system?

$$ [\text{Glucose}] \uparrow \Rightarrow [\text{cAMP}] \downarrow \Rightarrow \text{CRP inactive} $$

Question 1

Which of the following best describes the default state of gene expression in prokaryotes and the predominant type of transcriptional regulator?

Accepted Answer

Default state is activated; regulators are mostly repressors.

Question 2

A mutation abolishes the binding of the lac repressor to the operator. What is the most likely outcome for lac operon expression in the presence and absence of lactose?

Accepted Answer

Constitutive expression regardless of lactose presence.

Question 3

Which molecule acts as the inducer for the lac operon in E. coli, and what is its effect on the repressor?

Accepted Answer

Allolactose; it inactivates the repressor by changing its conformation.

Question 4

Which of the following best explains why the lac operon is not expressed at high levels even when the repressor is not bound, if glucose is present?

Accepted Answer

The lac promoter is a weak promoter and requires an activator for efficient transcription.

Question 5

Which of the following scenarios will result in the highest level of lac operon transcription?

Accepted Answer

Low glucose, high lactose

Question 6

What is the role of cAMP in the regulation of the lac operon?

Accepted Answer

It binds to the CRP (CAP) protein, activating it to bind DNA and promote transcription.

Question 7

Which of the following best describes the mechanism of attenuation in the trp operon?

Accepted Answer

It involves the formation of a stem-loop structure in mRNA that causes premature termination of transcription when tryptophan is abundant.

Question 8

A bacterium has a mutation in the trp repressor gene that prevents it from binding tryptophan. What is the expected effect on trp operon expression?

Accepted Answer

The operon will be constitutively expressed.

Question 9

Which of the following equations correctly represents the relationship between glucose, cAMP, and CRP activity in the lac operon system?

Accepted Answer

$$ [	ext{Glucose}] \uparrow \Rightarrow [	ext{cAMP}] \downarrow \Rightarrow 	ext{CRP inactive} $$

Question 10

Which of the following is a key difference between cis-acting elements and trans-acting factors?

Accepted Answer

Cis-acting elements regulate genes on the same DNA molecule; trans-acting factors are diffusible molecules that can regulate genes on different DNA molecules.

Question 11

A mutation in the lac operon prevents the repressor from binding the inducer. What is the expected phenotype?

Accepted Answer

The operon will be permanently repressed, regardless of lactose presence.

Question 12

Which of the following best explains why attenuation is an effective regulatory mechanism for the trp operon?

Accepted Answer

It allows the cell to sense and respond rapidly to changes in charged tRNA-Trp levels during translation.

Question 13

Which of the following statements about polycistronic mRNA is correct?

Accepted Answer

It contains multiple coding sequences, each with its own start and stop codon, allowing coordinated expression of functionally related genes.

Question 14

Which of the following best describes the effect of a mutation that abolishes the binding of CRP (CAP) to the lac operon?

Accepted Answer

The lac operon will not be efficiently expressed even in the absence of glucose and presence of lactose.

Question 15

Which of the following is true regarding the regulation of the trp operon?

Accepted Answer

Tryptophan acts as a corepressor, activating the repressor to bind the operator.

Question 16

Which of the following best describes the function of the operator in a bacterial operon?

Accepted Answer

It is a DNA sequence where repressors bind to block transcription.

Question 17

A bacterium is grown in a medium containing both glucose and lactose. What is the expected level of lac operon transcription?

Accepted Answer

Very low, because glucose inhibits cAMP production and CRP activation.

Question 18

Which of the following best explains why the lac operon is considered to be under dual control?

Accepted Answer

It is regulated by both an activator (CRP) and a repressor, responding to two different environmental signals.

Question 19

Which of the following is a real-world application of understanding the lac operon system?

Accepted Answer

Designing inducible gene expression systems in biotechnology using IPTG as an artificial inducer.

Prokaryotic Transcription Regulation: Operons and Gene Control in Bacteria

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