Drug inhibitor can act

Options

A. By breakingsubstrate molecule
B. By changing shape of active site on substrate
C. By blocking active site on substrate
D. Both 2 and 3

Answer

### Step-by-Step Solution:

1. **Understanding Drug Inhibitors**:
- Drug inhibitors are substances that can prevent or reduce the activity of enzymes. They can bind to the enzyme and interfere with its ability to catalyze reactions.

2. **Identifying the Mechanism of Action**:
- There are different ways in which drug inhibitors can act:
- **Blocking the Active Site**: Some inhibitors bind directly to the active site of the enzyme, preventing the substrate from attaching. This is known as competitive inhibition.
- **Changing the Shape of the Active Site**: Other inhibitors may bind to a different part of the enzyme, causing a conformational change that alters the shape of the active site, making it less effective or unable to bind the substrate.

3. **Evaluating the Options**:
- The question provides several options regarding how drug inhibitors can act:
- (1) By breaking the substrate molecule.
- (2) By changing the shape of the active site on the substrate.
- (3) By blocking the active site on the substrate.
- (4) Both 2 and 3.

4. **Analyzing Each Option**:
- **Option 1**: Incorrect. Drug inhibitors do not break the substrate molecule; they interfere with the enzyme's ability to act on the substrate.
- **Option 2**: Correct. Some inhibitors change the shape of the active site, preventing substrate binding.
- **Option 3**: Correct. Some inhibitors block the active site directly, preventing the substrate from binding.
- **Option 4**: Correct. Since both options 2 and 3 are correct, this option is valid.

5. **Conclusion**:
- The correct answer to the question is option (4) "Both 2 and 3," as drug inhibitors can act by changing the shape of the active site and blocking the active site on the substrate.