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BioTechnology QUESTION #10560
Question 1
Catabolite repression in microorganisms typically results in:
  • Simultaneous utilisation of all available carbon sources
  • Preferential use of the most favourable carbon source (e.g. glucose over lactose)✔️
  • Induction of all catabolic enzymes at equal rates
  • Irreversible repression of all biosynthetic operons
Correct Answer Explanation
Catabolite repression (glucose effect) occurs when a preferred carbon source (e.g. glucose) suppresses expression of enzymes needed to catabolise alternative substrates (e.g. lactose). In E. coli, glucose lowers cAMP levels, reducing activation of the CAP/CRP complex needed to transcribe the lac operon. This causes diauxic growth — sequential substrate utilisation.