Question 1

Which of the following best describes the central dogma of molecular genetics?

Accepted Answer

Information flows from DNA to RNA to protein.

Question 2

In the lac operon, what is the function of the lacY gene product?

Accepted Answer

It encodes permease, which facilitates the entry of lactose into the cell.

Question 3

Which of the following statements about the lac operon is TRUE?

Accepted Answer

The lac operon is under both negative and positive control mechanisms.

Question 4

A mutation in the operator region of the lac operon (lacO^c) results in which of the following?

Accepted Answer

Constitutive expression of the structural genes, regardless of lactose presence.

Question 5

Which of the following best explains the role of cyclic AMP (cAMP) in the regulation of the lac operon?

Accepted Answer

cAMP binds to the CAP protein, allowing it to bind DNA and promote transcription in the absence of glucose.

Question 6

In a partial diploid (merozygote) E. coli with the genotype lacI^− lacO^+ lacZ^+ / lacI^+ lacO^+ lacZ^−, what will be the phenotype regarding beta-galactosidase production in the absence of lactose?

Accepted Answer

Beta-galactosidase will not be produced.

Question 7

Which of the following is a key difference between inducible and repressible operon systems?

Accepted Answer

Inducible systems require an inducer to turn on gene expression, while repressible systems require a corepressor to turn off gene expression.

Question 8

What is the effect of a superrepressor mutation (lacI^s) in the lac operon?

Accepted Answer

The operon is always off, because the repressor cannot bind lactose and remains bound to the operator.

Question 9

Which of the following best describes a cis-acting element in gene regulation?

Accepted Answer

A DNA sequence that regulates genes located on the same DNA molecule.

Question 10

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

Accepted Answer

Low glucose, high lactose

Question 11

The trp operon is an example of a repressible system. What happens when tryptophan is present in high concentrations?

Accepted Answer

Tryptophan acts as a corepressor, activating the repressor and inhibiting transcription.

Question 12

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

Accepted Answer

A regulatory mechanism where transcription is prematurely terminated based on tryptophan levels.

Question 13

Which of the following is a function of small noncoding RNAs (sRNAs) in prokaryotic gene regulation?

Accepted Answer

They pair with mRNA to inhibit translation by masking the ribosome binding site.

Question 14

A mutation in the CAP-binding site of the lac operon would most likely result in which phenotype?

Accepted Answer

Reduced transcription of the operon, especially in the absence of glucose.

Question 15

Which of the following equations correctly represents the relationship between cAMP concentration and glucose concentration in E. coli?

Accepted Answer

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

Question 16

Which of the following is an example of a trans-acting element in the lac operon system?

Accepted Answer

The lac repressor protein

Question 17

Which of the following best describes the function of riboswitches?

Accepted Answer

They are regulatory segments of mRNA that bind small molecules to alter gene expression.

Question 18

In the context of the lac operon, what is the effect of a mutation in the promoter region (lacP^−)?

Accepted Answer

The structural genes are not transcribed, regardless of the presence of lactose or glucose.

Question 19

Which of the following best explains why the lac operon is considered polycistronic?

Accepted Answer

It produces a single mRNA that encodes multiple proteins.

Regulation of Gene Expression in Bacteria: The lac Operon and Mechanisms of Control

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