Question

Penicillin consists of a thiazolidine ring fused to a $\beta$-lactam ring. This antibiotic inhibits cell wall synthesis by inhibiting:

• A. $\beta$-lactamase
• B. Phosphodiesterase
• C. Transesterase
• D. Glycopeptide transpeptidase

Hint:

Penicillin = $\beta$-lactam = Inhibits Transpeptidase (cross-linking).

Answer 1

The Correct Option is D

Step 1: Concept
Bacterial cell walls (peptidoglycan) require cross-linking between peptide chains for structural integrity.

Step 2: Meaning
This cross-linking is catalyzed by enzymes called transpeptidases (also known as Penicillin-Binding Proteins or PBPs).

Step 3: Analysis
The $\beta$-lactam ring of penicillin mimics the D-Ala-D-Ala structure of the peptidoglycan precursor. The transpeptidase enzyme (Glycopeptide transpeptidase) mistakenly binds to the penicillin, which irreversibly inhibits the enzyme. This prevents the formation of cross-links, leading to a weak cell wall and eventual cell lysis.

Step 4: Conclusion
Penicillin's primary target is the glycopeptide transpeptidase enzyme. Final Answer: (D)