Q: Which equation represents the reaction catalyzed by β-galactosidase?

$$\text{Lactose} + \text{H}_2\text{O} \xrightarrow{\beta\text{-galactosidase}} \text{Glucose} + \text{Galactose}$$

Question 1

Which of the following best describes the default state of gene expression in prokaryotes, and how does it differ from eukaryotes?

Accepted Answer

Prokaryotic genes are usually on, but repression is common; eukaryotic genes are mostly off and require activation.

Question 2

In the lac operon, what is the effect of an I− mutation (mutant repressor gene) on gene expression?

Accepted Answer

The operon is always induced, regardless of lactose presence.

Question 3

Which molecule acts as the true inducer of the lac operon in E. coli?

Accepted Answer

Allolactose

Question 4

What is the role of the lacY gene product in lactose metabolism?

Accepted Answer

It facilitates the entry of lactose into the bacterial cell.

Question 5

Which equation represents the reaction catalyzed by β-galactosidase?

Accepted Answer

$$	ext{Lactose} + 	ext{H}_2	ext{O} \xrightarrow{\beta	ext{-galactosidase}} 	ext{Glucose} + 	ext{Galactose}$$

Question 6

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

Accepted Answer

The trp operon is a repressible system that is turned off in the presence of tryptophan.

Question 7

What is the effect of glucose on the lac operon, and which molecule mediates this effect?

Accepted Answer

Glucose decreases cAMP levels, which reduces CAP binding and diminishes lac operon expression.

Question 8

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

Accepted Answer

Attenuation is a mechanism where the presence of tryptophan causes premature termination of transcription in the leader region.

Question 9

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

Accepted Answer

Cis-acting elements are DNA sequences near the genes they regulate, while trans-acting elements are proteins or RNAs that can diffuse and act elsewhere.

Question 10

A bacterial cell is exposed to both lactose and glucose. What is the expected outcome for lac operon expression?

Accepted Answer

Low expression of lac operon genes due to catabolite repression.

Question 11

Which of the following best explains the effect of an OC (operator-constitutive) mutation in the lac operon?

Accepted Answer

The repressor protein is unable to bind the operator, resulting in continuous expression of structural genes.

Question 12

Which of the following equations correctly represents the conversion of ATP to cAMP catalyzed by adenylate cyclase?

Accepted Answer

$$	ext{ATP} \xrightarrow{	ext{adenylate cyclase}} 	ext{cAMP} + 2	ext{P}_i$$

Question 13

Which of the following statements about polycistronic mRNA is correct?

Accepted Answer

Polycistronic mRNA is transcribed from a cluster of genes and encodes multiple proteins.

Question 14

Which of the following best describes the function of riboswitches in bacterial gene regulation?

Accepted Answer

Riboswitches are alternative forms of mRNA secondary structure that bind small ligands and induce conformational changes, affecting transcription or translation.

Question 15

Which scenario would result in maximum expression of the lac operon?

Accepted Answer

Lactose present, glucose absent

Question 16

Which of the following is a plausible outcome of a lacIs (superrepressor) mutation?

Accepted Answer

The operon is always repressed, even in the presence of lactose.

Question 17

Which of the following best describes the effect of small noncoding RNAs (snRNAs) in bacterial gene regulation?

Accepted Answer

snRNAs can either repress or activate translation by binding to mRNAs and affecting ribosome binding sites.

Question 18

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

Accepted Answer

Using the lac operon to control the expression of recombinant proteins in E. coli by adding IPTG as an inducer.

Regulation of Gene Expression in Bacteria: The lac and trp Operons

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