Question

An apoenzyme is a
A) Protein
B) Lipid
C) Sugar
D) Vitamin

Answer 1

Hint: Apoenzymes are inactive forms of enzymes possessing the ability of binding the substrate with an affinity to holoenzyme; however, lack the efficacy of transforming the substrate back to the product.

Complete Answer:
A) Option A: Apoenzyme is a protein component of the holoenzyme. The moment you separate this protein component from its cofactor group, it renders itself as an inactive entity. The holoenzyme cofactor thus becomes the non protein component thereby becoming responsible for the enzymatic activity. Thus, this is the correct option.

B) Option B: Lipids do not possess the ability of binding the substrate. Thus, this is the incorrect option.

C) Option C: Sugars do not possess the ability of binding the substrate. Thus, this is the incorrect option.

D) Option D: Vitamins lack the ability of binding the substrate. Thus, this is the incorrect option.

Thus, the correct option for the given question is A i.e. protein.

Additional information: The characteristics of enzymes are,
- They are highly specific, i.e. they bind only to a particular substrate.
- They are temperature and pH specific.
- They are very efficient.
- They remain unchanged during the reaction.
- They do not affect the equilibrium constant of the reaction.
- They increase the speed of the reaction.
- They are involved in chemical reactions like- digestion, blood coagulation, growth reproduction, etc.
- They have defined 3D structure and are made up of protein molecules.

Note: When an apoenzyme combines with a cofactor, it becomes a holoenzyme. Examples of the holoenzyme are DNA polymerase and RNA polymerase.