Question

The Lac Operon is turned on when allolactose molecules bind to :

• A. Promoter site
• B. Operator site
• C. mRNA
• D. Repressor protein

Answer 1

Answer: (D)

Repressor protein

Answer 2

Lac operon is the prototype operon in bacteria, which codes for genes (i, z, y, a) responsible for metabolism of lactose. The gene i codes for repressor, z for $\beta$-galactosidase. y for permease and a for transacety lase. The repressor o f the operon is synthesised (all-the-timeconstitutivelv) from the i gene. The repressor protein binds to the operator region of the operon and prevents RNA polymerase from transcribing the operon. In the presence of an inducer, such as lactose or allolactose, the repressor is inactivated by interaction with the inducer. This allows RNA polymerase access to the promoter and transcription proceeds.