Q.2 Identify the statement that is TRUE of operons.
(A) Fine regulation of the expression of individual genes are made possible by operons
(B) Only genes involved in carbohydrate metabolism are present in operons
(C) Feedback inhibition of the biosynthesis of multiple enzymes by a single small molecule is made
possible by operons
(D) In the case of inducible operons, the inducer binds to the operator

Correct Answer: (C)

Operons enable coordinated regulation of multiple genes as a single transcriptional unit, allowing feedback inhibition by a single small molecule to control biosynthesis of several enzymes simultaneously.​

Option Analysis

(A) False

Operons coordinate expression of multiple related genes together, not fine regulation of individual genes, which occurs via separate promoters or enhancers in eukaryotes.​

(B) False

Operons include genes for amino acid biosynthesis (trp operon), nucleotide synthesis (his operon), and others beyond just carbohydrate metabolism like lac operon.​

(C) True

In repressible operons like trp, high tryptophan levels activate a repressor that binds the operator, inhibiting transcription of all enzymes in the pathway via a single end-product signal.​

(D) False

In inducible operons like lac, the inducer (allolactose) binds the repressor protein, causing it to release from the operator; the inducer does not bind the operator directly.​

The true statement about operons revolves around their role in efficient gene regulation, particularly feedback inhibition of multiple enzymes by a single small molecule. This mechanism, vital for CSIR NET Life Sciences preparation, allows bacteria to coordinate metabolic pathways through operons like trp.​

What Are Operons?

Operons are clusters of prokaryotic genes transcribed as one polycistronic mRNA under a single promoter and operator. They enable coordinate regulation for related functions, conserving energy by turning pathways on or off together.​

• Lac operon: Inducible, for lactose catabolism.

• Trp operon: Repressible, for tryptophan biosynthesis.​

Why Option C is Correct

Feedback inhibition pairs with operon repression: excess end-product (e.g., tryptophan) binds the repressor, blocking transcription of all pathway enzymes at once. This single-molecule control exemplifies operon efficiency, unlike individual enzyme inhibition.​

Common Misconceptions

Inducers bind repressors, not operators directly—key for inducible systems. Operons span diverse metabolisms, not just carbohydrates. Fine individual control happens outside operons.​