(A) inactivating catabolic enzymes

(B) inhibiting synthesis of total RNA

(C) regulating expression of genes required for utilization of less-efficient metabolites

(D) inhibiting translation of mRNAs encoding catabolic enzymes

Catabolite repression prioritizes efficient carbon sources like glucose in bacteria, preventing wasteful enzyme production. This SEO article explains Q.70 mechanism with the correct answer and all options for microbiology exams.

Correct Answer

The correct answer is (C) regulating expression of genes required for utilization of less-efficient metabolites.

When glucose is available, cAMP levels drop, preventing CAP activation of alternative carbon source operons like lac. This represses synthesis of unnecessary catabolic enzymes (e.g., β-galactosidase for lactose), saving energy until glucose depletes.

Option Breakdowns

(A) inactivating catabolic enzymes

Catabolite repression prevents new enzyme synthesis at transcription, not inactivating existing proteins.
Existing enzymes continue functioning; regulation occurs preventively.

(B) inhibiting synthesis of total RNA

Repression targets specific operons, not global RNA polymerase activity or total transcription.
Housekeeping genes remain expressed normally.

(C) regulating expression of genes required for utilization of less-efficient metabolites

Glucose represses lac, ara, and other operons via cAMP-CAP, enabling diauxic growth with glucose first.
Optimizes resource allocation in mixed carbon environments.

(D) inhibiting translation of mRNAs encoding catabolic enzymes

Primary control is transcriptional (promoter binding); no direct ribosome/mRNA translation block.
mRNAs for repressed genes aren’t even transcribed.