Among the statement given below, which statements /s is / are correct regarding the relationship between enzyme and substrate ?
I. Above a certain concentration of substrate , an enzyme reaches its maximum rate of reaction
II. Increasing the substrate concentration to a higher level doesn't reverse the effects of a competitive inhibitor.
III At high substrate concentration , a non competitive inhibitor no longer affects the enzyme activity .
IV. The higher the concentration of substrate the faster an enzyme can cataylse a reaction.

Options

A. I and II only
B. I,II and IV
C. I only
D. III and IV only

Answer

To solve the question regarding the relationship between enzyme and substrate, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement I**: "Above a certain concentration of substrate, an enzyme reaches its maximum rate of reaction."
- **Analysis**: This statement is correct. Enzymes have a maximum rate of reaction (Vmax) that they can achieve, which occurs when all active sites of the enzyme molecules are saturated with substrate. Beyond this point, increasing substrate concentration does not increase the rate of reaction.
- **Conclusion**: Correct.

2. **Statement II**: "Increasing the substrate concentration to a higher level doesn't reverse the effects of a competitive inhibitor."
- **Analysis**: This statement is incorrect. Competitive inhibitors compete with the substrate for the active site of the enzyme. Increasing the substrate concentration can outcompete the inhibitor, thereby reversing its effects.
- **Conclusion**: Incorrect.

3. **Statement III**: "At high substrate concentration, a non-competitive inhibitor no longer affects the enzyme activity."
- **Analysis**: This statement is also incorrect. Non-competitive inhibitors bind to an enzyme regardless of whether the substrate is bound or not. Therefore, even at high substrate concentrations, a non-competitive inhibitor can still inhibit enzyme activity.
- **Conclusion**: Incorrect.

4. **Statement IV**: "The higher the concentration of substrate, the faster an enzyme can catalyze a reaction."
- **Analysis**: This statement is misleading. While an increase in substrate concentration can initially increase the rate of reaction, this only occurs up to a certain point (Vmax). Beyond that, the rate of reaction levels off and does not increase further with additional substrate.
- **Conclusion**: Incorrect.

### Final Evaluation:
- The only correct statement is **Statement I**. Therefore, the correct answer is that only Statement I is correct.