Question

Lactose metabolising enzyme, produced in the presence of lactose only is

• A. Inducible enzyme
• B. Constitutive enzyme
• C. Repressible enzyme
• D. Regulatory enzyme

Answer 1

The correct option is A Inducible enzyme

The lac operon
The lac operon is an inducible operon system which gets activated when an inducer (lactose or allolactose) is present in the cell.

Inducible enzyme
An inducible enzyme is the one which is produced in the presence of a substance (inducer) in the cell.
Lactose when present in the cell, inactivates the repressor. This allows the transcription of structural genes such as lac z, lac y and lac a for its metabolism. Thus, lactose metabolising enzymes are inducible enzymes.

Repressible enzyme
Repressible enzymes are the ones which are transcribed and translated normally in the cell. However, the production gets inhibited in the presence of a metabolite that activates the repressor.

Regulatory enzyme
Regulatory enzymes are those enzymes which regulate the various physiological processes. For example, kinases are the regulatory enzymes facilitating the transfer of phosphate groups to the specific substrates.

Constitutive enzyme
Constitutive enzymes are the enzymes which are produced all the time in the cell irrespective of the presence of an inducer or repressor.

Final answer
(A) Inducible enzyme