Question 1

Which of the following best describes the function of an operon in prokaryotes?

Accepted Answer

A group of genes with a common purpose, controlled by a single promoter and transcribed as one mRNA.

Question 2

What happens to the trp operon when tryptophan concentration is high in a prokaryotic cell?

Accepted Answer

Tryptophan binds to the repressor, activating it, which then binds to the operator and blocks transcription.

Question 3

Which of the following is an example of a repressible operon?

Accepted Answer

trp operon

Question 4

In the context of gene regulation, what is the main difference between positive and negative transcriptional control?

Accepted Answer

Positive control requires stimulation for transcription, while negative control involves blocking transcription of genes whose default state is 'on'.

Question 5

Which of the following best explains why cells only use about 5-20% of their genes at a time?

Accepted Answer

Gene expression is regulated based on cell type and internal conditions, such as stage in the cell cycle.

Question 6

A mutation causes the trp repressor protein to be unable to bind tryptophan. What is the most likely consequence for the cell?

Accepted Answer

The trp operon will be continuously transcribed, even when tryptophan levels are high.

Question 7

Which of the following statements about the trp operon is correct?

Accepted Answer

It is regulated by a repressor protein that is activated by binding tryptophan.

Question 8

Which of the following best describes feedback inhibition in the context of tryptophan synthesis?

Accepted Answer

The end product, tryptophan, inhibits the activity of enzymes involved in its own synthesis.

Question 9

Which of the following equations best represents the relationship between DNA, RNA, and protein in gene expression?

Accepted Answer

$$DNA \rightarrow RNA \rightarrow Protein$$

Question 10

A researcher discovers a prokaryotic operon that is only transcribed when a specific nutrient is absent. Which type of operon is this most likely to be?

Accepted Answer

A repressible operon

Question 11

Which of the following is true about the operator region in an operon?

Accepted Answer

It is a DNA sequence where the repressor protein can bind to regulate transcription.

Question 12

If a mutation causes the trp repressor to be permanently active, what would be the effect on the cell's ability to synthesize tryptophan?

Accepted Answer

The cell would be unable to transcribe the trp operon, leading to a deficiency in tryptophan synthesis.

Question 13

Which of the following best describes the role of allosteric regulation in the trp operon system?

Accepted Answer

Tryptophan binds to the repressor, causing an allosteric change that enables the repressor to bind the operator.

Question 14

Which of the following scenarios best illustrates negative transcriptional regulation?

Accepted Answer

A repressor protein binds to the operator, preventing RNA polymerase from transcribing the operon.

Question 15

Which of the following is a key feature of prokaryotic gene regulation that is rare in eukaryotes?

Accepted Answer

Genes organized into operons and transcribed as a single mRNA.

Question 16

A cell is found to have high levels of tryptophan and low levels of trp operon mRNA. Which regulatory mechanism is most likely responsible for this observation?

Accepted Answer

Tryptophan activates the repressor, which binds the operator and blocks transcription.

Question 17

Which of the following best describes the relationship between feedback inhibition and gene regulation in the tryptophan biosynthetic pathway?

Accepted Answer

Feedback inhibition regulates enzyme activity, while gene regulation controls the transcription of enzymes for tryptophan synthesis.

Gene Regulation in Prokaryotes: The trp Operon and Mechanisms of Control

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