Prosthetic groups differ from co-factors in that the former is

Options

A. tightly bound to the coenzyme
B. tightly bound to the apoenzyme
C. loosely bound to the inorganic catalyst
D. tightly bound to the active site

Answer

To solve the question regarding how prosthetic groups differ from cofactors, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definitions**:
- **Enzymes**: Biological catalysts that speed up reactions.
- **Apoenzyme**: The protein part of an enzyme without its cofactors.
- **Cofactors**: Non-protein components that assist enzymes in catalyzing reactions. They can be further classified into prosthetic groups, coenzymes, and metal ions.

2. **Identify Prosthetic Groups**:
- Prosthetic groups are a type of cofactor that are tightly bound to the apoenzyme. This means they are not easily removed and are integral to the enzyme's function.

3. **Differentiate from Other Cofactors**:
- Other cofactors, such as coenzymes, are usually loosely bound to the enzyme and can dissociate after the reaction. Metal ions can also serve as cofactors but do not have the same binding characteristics as prosthetic groups.

4. **Analyze the Options**:
- **A. Tightly bound to coenzyme**: This is incorrect because prosthetic groups are not bound to coenzymes.
- **B. Tightly bound to apoenzyme**: This is correct as prosthetic groups are indeed tightly bound to the apoenzyme.
- **C. Loosely bound to the inorganic catalyst**: This is incorrect; prosthetic groups are not loosely bound.
- **D. Tightly bound to the active site**: While prosthetic groups are part of the active site, the defining characteristic is their tight binding to the apoenzyme.

5. **Select the Correct Answer**:
- Based on the analysis, the correct answer is **B. Tightly bound to the apoenzyme**.