This stops the production of the polypeptide. If the sugar enters the cell, the operon will be switched on and produce the enzymes needed to digest the lactose. Lactose metabolism in E. coli is programmed by the lac operon which has three structural genes. Z codes for B-glactosidase which hydrolyzes lactose. Y codes for permease, a membrane protein that transports lactose into the cell, and lac A codes for transacetylase, an enzyme that has no known action in lactose metabolism.
Lactose acts as an inducer to turn on the operon.
Repressible Enzymes Inducible Enzymes 1. Their genes are switched on until 1. There genes are switched off specific metabolite activates the repressor until a specific metabolite inactivates the repressor. Generally function in an anabolic pathway. Functions in catabolic pathways.