Explain the regulation of lac operon in absence and presence of lactose as an inducer.

Explanation

In absence of inducer - lactose.
Repressor protein is produced from Lac - i- gene binds to operator region of the operon and prevents RNA polymerase from transcribing the operon.
Switch óff - structural genes Lac - Z, Lac - Y & Lac - a no transcription and donot produce any enzymes.
In presence of Inducer - Lactose
Repressor protein produced by : gene binds to inducer and is inactivated by interaction with the inducer
RNA polymerase enzyme binds to promoter region and transcribes structural genes Lac - Z, Lac - Y and Lac - A