Question

Explain with the help of a well-labelled diagram how the lac operon operates in E. coli:

In presence of an inducer.

Answer 1

1. Lactose (inducer) binds to the repressor protein (LacI), inactivating it.
2. This enables the lac operon genes to be transcribed by RNA polymerase when it binds to the promoter.
3. The genes LacZ, LacY, and LacA generate lactose-digesting enzymes:
   • LacZ: B-galactosidase (breaks lactose into glucose + galactose).
   • LacY: Permease (transports lactose into the cell).
   • LacA: Transacetylase (function unclear).