Answer
The protein portion of an enzyme is called:
- Cofactor
- Coenzyme
- Apoenzyme
- Prosthetic group
✅ Correct Answer: (3) Apoenzyme
🧬 Detailed Explanation:
Enzymes are biological catalysts composed of two major parts:
- Apoenzyme – the protein portion of the enzyme.
- Cofactor – the non-protein part, which can be a metal ion or organic molecule.
When these two parts come together, they form a holoenzyme (the active enzyme).
🔍 Key Definitions:
- Apoenzyme: The inactive protein part of an enzyme, requiring a cofactor for activity.
- Cofactor: A non-protein helper molecule, either inorganic (metal ions) or organic.
- Coenzyme: An organic cofactor, often derived from vitamins (e.g., NAD⁺, FAD).
- Prosthetic group: A cofactor that is permanently and tightly bound to the enzyme.
📌 Summary:
| Term | Nature | Role |
|---|---|---|
| Apoenzyme | Protein | Inactive on its own; needs a cofactor |
| Cofactor | Non-protein | Helps in enzyme activity |
| Coenzyme | Organic cofactor | Transfers chemical groups between molecules |
| Prosthetic group | Bound cofactor | Permanently attached, essential for function |
🔬 Final Note: An apoenzyme alone is inactive. It becomes a functional holoenzyme only when combined with the right cofactor.