Q: Which formula correctly represents the relationship between glucose, cAMP, and CRP activity in the lac operon?

$$[\text{cAMP}] \propto \frac{1}{[\text{Glucose}]}$$

Question 1

Which of the following best describes the default state of gene expression in prokaryotes and the role of most transcriptional regulators?

Accepted Answer

Genes are usually activated, and most regulators are repressors.

Question 2

A mutation abolishes the DNA binding domain of the lac repressor protein. What is the most likely effect on lac operon expression?

Accepted Answer

The lac operon will be constitutively expressed, regardless of lactose presence.

Question 3

Which molecule acts as the inducer for the lac operon by binding to the repressor and causing its release from the operator?

Accepted Answer

Allolactose

Question 4

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

Accepted Answer

cAMP binds to the CAP/CRP protein, activating it to bind DNA and promote transcription.

Question 5

Which of the following best explains why the lac operon is not expressed in the presence of glucose, even if lactose is available?

Accepted Answer

Glucose prevents the formation of cAMP, so CAP/CRP cannot activate transcription.

Question 6

Which statement correctly describes the difference between cis-acting elements and trans-acting factors?

Accepted Answer

Cis-acting elements are DNA sequences that regulate the same gene they belong to; trans-acting factors are proteins produced by different genes that regulate other genes.

Question 7

A bacterial operon produces a polycistronic mRNA. What does this mean?

Accepted Answer

The mRNA contains coding sequences for several proteins, each with its own start and stop codon.

Question 8

Which of the following scenarios will result in maximal expression of the lac operon?

Accepted Answer

Low glucose, high lactose

Question 9

What is the effect of a mutation in the operator sequence of the lac operon that prevents repressor binding?

Accepted Answer

The lac operon will be constitutively expressed.

Question 10

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

Accepted Answer

Attenuation involves the formation of a stem-loop structure in the mRNA leader sequence, causing premature termination of transcription when tRNA-Trp levels are high.

Question 11

Which formula correctly represents the relationship between glucose, cAMP, and CRP activity in the lac operon?

Accepted Answer

$$[	ext{cAMP}] \propto \frac{1}{[	ext{Glucose}]}$$

Question 12

In the trp operon, what is the role of tryptophan?

Accepted Answer

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

Question 13

Which of the following is true about the lac operon promoter?

Accepted Answer

It is a weak promoter that requires an activator (CAP/CRP) for efficient RNA polymerase recruitment.

Question 14

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 CAP activation.

Question 15

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

Accepted Answer

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

Question 16

What is the effect of a mutation in the lac repressor gene that prevents inducer binding?

Accepted Answer

The lac operon will be permanently repressed, even in the presence of lactose.

Question 17

Which of the following is a consequence of the polycistronic nature of bacterial operons?

Accepted Answer

Multiple proteins are translated from a single mRNA transcript.

Question 18

Which of the following best describes the dual control of the trp operon?

Accepted Answer

It is regulated by a repressor at the promoter and attenuation at the leader sequence.

Question 19

Which scenario would result in the formation of the attenuator terminator in the trp operon?

Accepted Answer

High levels of free tryptophan and high levels of tRNA-Trp

Prokaryotic Transcription Regulation: Operons and Gene Control in Bacteria

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