Question

Assertion
A coenzyme or metal ion tightly bound to enzyme protein is called a prosthetic group.
Reason
A complete catalytically active enzyme together with its bound prosthetic group is called apoenzyme.

A. Both assertion and reason are correct and reason is the correct explanation for assertion.
B. Both assertion and reason are correct but reason is not the correct explanation for assertion.
C. Assertion is correct but reason is incorrect.
D. Both assertion and reason are incorrect.

Answer 1

Enzymes are proteins that act as biological catalysts. A holoenzyme is composed of an apoenzyme along with its bound prosthetic group that is not released during the catalytic reaction.

Complete answer:
Option (A) is incorrect. Only the assertion is correct while the reason is incorrect because a complete catalytically active enzyme together with its bound prosthetic group is called holoenzyme but not apoenzyme.
Option (B) is incorrect. Only the assertion is correct and the reason is incorrect because the apoenzyme is an inactive part of a completely catalytically active enzyme.
Option (C) is correct. Enzymes are catalytically active proteins. Some of the enzymes are active fully on their own but some require bound cofactors to become fully active. These cofactors are non-protein parts of an enzyme that may be either metal ion or organic chemicals. A prosthetic group is called a cofactor or metal ion that is tightly bound to an enzyme. Thus, cofactors bound to an inactive enzyme (or apoenzyme) form a complete catalytically active enzyme that is known as the holoenzyme.
Option (D) is incorrect. The assertion is correct because it is the prosthetic group that is tightly bound to an enzyme but the reason is not correct because the apoenzyme is an inactive part of the holoenzyme.

Hence, the correct answer is option (C).

Note: Cofactors are non-protein parts of an enzyme that can be either metal ions or organic molecules. The cofactor that is an organic molecule and loosely attached to the apoenzyme is called a coenzyme while the cofactor that is metal ion and tightly bound to an apoenzyme is called a prosthetic group.