Q: Which equation correctly represents the conversion of ATP to cAMP by adenylyl cyclase?

$$\mathrm{ATP} \xrightarrow{\text{adenylyl cyclase}} \mathrm{cAMP} + \mathrm{PP_i}$$

Question 1

Which of the following best describes the function of the lac operon in E. coli?

Accepted Answer

It encodes enzymes necessary for the metabolism of lactose.

Question 2

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

Accepted Answer

It acts as an inducer by binding to the repressor and preventing it from binding to the operator.

Question 3

Which of the following statements about the lacI gene is correct?

Accepted Answer

It encodes a trans-acting repressor protein that can diffuse throughout the cell.

Question 4

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

Accepted Answer

Constitutive expression of the lac operon, regardless of lactose presence.

Question 5

Which of the following best explains why the lac operon is not highly expressed when both glucose and lactose are present?

Accepted Answer

Low levels of cAMP prevent CAP from binding to the CAP site, reducing transcription.

Question 6

Which of the following is a correct description of a repressible operon?

Accepted Answer

It is typically involved in anabolic pathways and is turned off by the end product of the pathway.

Question 7

Which equation correctly represents the conversion of ATP to cAMP by adenylyl cyclase?

Accepted Answer

$$\mathrm{ATP} \xrightarrow{	ext{adenylyl cyclase}} \mathrm{cAMP} + \mathrm{PP_i}$$

Question 8

In an E. coli strain with genotype $$I^+O^+Z^-Y^+$$, what is the expected phenotype for beta-galactosidase and permease production in the presence of lactose?

Accepted Answer

No beta-galactosidase, inducible permease

Question 9

Which of the following is an example of negative control of gene expression?

Accepted Answer

A repressor protein binding to the operator to block transcription

Question 10

Which of the following best describes the effect of a functional lacI gene introduced on a plasmid into a lacI mutant E. coli?

Accepted Answer

It restores inducible regulation of the lac operon, demonstrating that lacI is trans-acting.

Question 11

Which of the following mechanisms can regulate gene expression at the posttranslational level?

Accepted Answer

Covalent modification of proteins

Question 12

Which of the following statements about small effector molecules is correct?

Accepted Answer

They can either increase or decrease transcription depending on the gene and effector.

Question 13

Which of the following is a real-life application of feedback inhibition in bacteria?

Accepted Answer

The end product of a metabolic pathway inhibits the first enzyme in the pathway.

Question 14

Which of the following best describes the function of antisense RNA in gene regulation?

Accepted Answer

It binds to mRNA and prevents translation from starting.

Question 15

Which of the following scenarios would result in the highest expression of the lac operon?

Accepted Answer

Lactose present, glucose absent

Question 16

Which of the following is true regarding the difference between cis-acting and trans-acting elements?

Accepted Answer

Cis-acting elements affect only genes on the same DNA molecule, while trans-acting elements can diffuse and affect genes on different DNA molecules.

Question 17

Which of the following best describes attenuation as a regulatory mechanism?

Accepted Answer

Transcription terminates soon after it has begun due to the formation of a transcriptional terminator in the mRNA.

Question 18

Which of the following is a correct match between a lac operon component and its function?

Accepted Answer

LacY: gene encoding lactose permease

Question 19

Which of the following best explains why operons involved in catabolism are typically inducible?

Accepted Answer

The substrate to be broken down acts as an inducer, turning on the operon only when needed.

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

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