The first step of an enzyme catalysed reaction is :

Options

A. The enzyme breaks the chemical bond of the substrate .
B. The enzyme releases the product of the reaction.
C. The substrate binds to the active site of the enzyme.
D. The binding site reacts with the substrate forming the enzyme product complex.

Answer

To solve the question regarding the first step of an enzyme-catalyzed reaction, we can break it down step by step:

### Step-by-Step Solution:

1. **Understanding Enzymes**:
- Enzymes are biological catalysts that speed up chemical reactions in living organisms. They are primarily made of proteins.

2. **Enzyme-Substrate Interaction**:
- The first step in an enzyme-catalyzed reaction involves the enzyme interacting with its substrate. This interaction occurs at a specific region on the enzyme known as the active site.

3. **Binding of Substrate**:
- The substrate binds to the active site of the enzyme. This step is crucial as it forms the enzyme-substrate complex.

4. **Formation of the Enzyme-Substrate Complex**:
- Once the substrate is bound to the active site, the enzyme and substrate undergo a series of interactions that lead to the formation of the enzyme-substrate complex.

5. **Subsequent Steps**:
- After the enzyme-substrate complex is formed, the enzyme catalyzes the conversion of the substrate into products. This involves breaking and forming chemical bonds.

6. **Release of Products**:
- Finally, the products are released from the enzyme, which can then participate in another reaction cycle.

### Conclusion:
The first step of an enzyme-catalyzed reaction is when the **substrate binds to the active site of the enzyme**.

### Answer:
**Option C: The substrate binds to the active site of the enzyme.**

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