Enzymes catalyse reactions by

Options

A. Decreasing activation energy
B. Increasing activation energy
C. Without changing activation energy
D. All the above

Answer

**Step-by-Step Solution:**

1. **Understanding Enzymes**: Enzymes are biological catalysts that facilitate biochemical reactions in living organisms. They are crucial for various metabolic processes.

2. **Role of Enzymes**: The primary function of enzymes is to lower the activation energy required for a reaction to occur. Activation energy is the minimum energy needed for reactants to undergo a chemical transformation.

3. **Lowering Activation Energy**: By lowering the activation energy, enzymes increase the rate of the reaction. This means that reactions can occur more quickly and efficiently in the presence of enzymes.

4. **Induced Fit Model**: When a substrate (the molecule upon which an enzyme acts) binds to the enzyme, the enzyme may change its shape slightly to fit the substrate better. This is known as the "induced fit" model. The precise orientation of the enzyme and substrate enhances the catalytic activity.

5. **Active Site**: The active site of the enzyme is the specific region where the substrate binds. The shape and chemical environment of the active site facilitate the conversion of the substrate into products.

6. **Conclusion**: Therefore, enzymes catalyze reactions primarily by lowering the activation energy, which in turn increases the rate of the reaction.

**Final Answer**: Enzymes catalyze reactions by lowering the activation energy.

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