Question

In a lac operon system, i codes for

• A. Inducer
• B. Repressor
• C. Promoter
• D. $\beta$-galactosidase

Answer 1

Answer: (B)

Repressor

The lac operon (lactose operon) is an operon required for the transport and metabolism of lactose in Escherichia coli and many other enteric bacteria. It is expressed only when lactose is present and glucose is absent. The lac operon contains three genes: lacZ, lacY, and lacA. Z codes for $\beta$-galactosidase (an enzyme that splits lactose into monosaccharides), y gene codes for permease (a membrane-embedded transporter that helps bring lactose into the cell), which increases the permeability of the cell and a gene encodes a transacetylase. i gene codes for the repressor of the lac operon. The operator is a negative regulatory site bound by the lac repressor protein. The lac repressor is a protein that represses (inhibits) transcription of the lac operon. It does this by binding to the operator, which partially overlaps with the promoter.

So, the answer is B.