Question

In $lac$ operon, ‘inducer lactose’ serves as an enzyme-substrate for the enzyme

• A. Permease
• B. ꞵ-galactosidase
• C. Endonuclease
• D. Transacetylase

Answer 1

The correct option is B ꞵ-galactosidase

The $lac$ operon
The $lac$ operon is an inducible operon system that remains usually in a repressed condition and gets activated only when the substance to be metabolised (lactose) is present.
Inducer
Inducer is a chemical which forms an inducer repressor complex. This prevents the repressor from binding to the operator gene.
Transacetylase
Transacetylase is an enzyme encoded by the lac a gene of lac operon.
It transfers the acetyl group to β-galactosides etc.
Permease
Permease is an enzyme encoded by gene lac y of lac operon. It increases the permeability of the cell to lactose.
ꞵ-galactosidase
β-galactosidase is an enzyme encoded by the lac z gene and hydrolyses lactose into glucose and galactose. Thus, lactose, an inducer of lac operon, acts as a substrate for the enzyme β-galactosidase.
Endonuclease
Endonucleases are enzymes that cleave DNA at a point within the DNA strand but not at the ends.
Final answer
(C) ꞵ-galactosidase