Penicillin is produced by fungi of genus Penicllium notatum. The penicillin shows antibacterial action by rupturing the cell wall of growing bacterial cells. Penicillin is an antibacterial agent, which has a broad spectrum effect on various bacteria. The antibacterial action is selective for group of organism mainly gram positive groups.
Penicillin attacks the NAM (N-acetylmuramic acid) and NAG (N-acetylglucosamine) of the cell wall. The cell wall acts as a barrier to maintain the osmotic balance of the cell. It contains four membered β-lactam rings fused to a five-membered thiazolidine ring.
The penicillin analogue when encounters the active site of the transpeptidase enzyme leads the serine moiety to donate a lone pair of electrons. It ruptures the ring structure. The ring would again regain its cyclic structure by accepting electrons from the hydrogen present in the ring itself.
This recovers the structures and no longer the penicillin blocks the active site of the enzyme. It would no longer show the inhibitory role and the enzyme transpeptidase would continue crosslinking. The cell wall is formed without any loose ends to leak the cellular material.