The mode of action of penicillin on bacterial growth is by inhibition of :

Options

A. Peptidoglycan synthesis
B. Protein synthesis
C. mRNA synthesis
D. Paramylum synthesis

Answer

To solve the question regarding the mode of action of penicillin on bacterial growth, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Nature of Penicillin**:
- Penicillin is an antibiotic that is primarily effective against bacteria, particularly Gram-positive bacteria.

2. **Identify the Target of Penicillin**:
- Penicillin works by inhibiting the synthesis of the bacterial cell wall, which is crucial for bacterial survival and growth.

3. **Focus on Peptidoglycan**:
- The cell wall of Gram-positive bacteria is mainly composed of peptidoglycan. This structure provides rigidity and strength to the bacterial cell wall.

4. **Role of Transpeptidase**:
- The enzyme transpeptidase is essential for the cross-linking of peptidoglycan layers, which is a critical step in cell wall synthesis.

5. **Mechanism of Action**:
- Penicillin inhibits the activity of transpeptidase, preventing the formation of peptidoglycan. Without proper cell wall synthesis, bacteria cannot maintain their structure, leading to cell lysis and death.

6. **Conclusion**:
- Therefore, the mode of action of penicillin on bacterial growth is by the inhibition of peptidoglycan synthesis.

### Final Answer:
The mode of action of penicillin on bacterial growth is by inhibition of **peptidoglycan synthesis**.

---