Final answer:
Catabolite repression is a global regulatory mechanism that inhibits the expression of operons encoding substrate use pathways for substrates other than glucose when glucose is present.
Step-by-step explanation:
Catabolite repression is a global regulatory mechanism that inhibits the expression of operons encoding substrate use pathways for substrates other than glucose when glucose is present. It is a form of negative regulation, where the presence of glucose prevents the activation of genes required for the utilization of alternative sugars as fuel. This mechanism is mediated by the catabolite activator protein (CAP) and cyclic AMP (cAMP), which bind to the promoter regions of the operons controlling the processing of alternative sugars and enhance transcription.