Mode of action of penicillin (antibiotics)



Antibiotics function according to their structures. β-lactam analogues (penicillin) function by exerting their effects by disrupting the creation of peptidoglycan (core stress bearing network in bacterial cell wall). The destruction occurs either by blocking the construction of sub-units of peptidoglycan or by barring their association in existing network. 


As can be seen in the reaction, four-membrane β-lactam makes amide susceptible to nucleophile acyl substitution. The action of antibiotics occurs due to their abilities to acylate the amino group (-NH2) of enzyme that is responsible for synthesis of bacterial cell wall. The question always arises, if penicillin has effect on mammalian cells? The answer is no, since mammalian cells are not enclosed by cell walls. In this process, penicillin changes active enzyme into inactive enzyme as indicated above thus inhibiting its dangerous action on cells. 
How does resistance to penicillin occur?
In some situations resistance to penicillin is experienced. This occurs by bacteria becoming resistant through mutation and in the process produce β-lactamase which facilitates the opening of β-lactam. The opened ring is inactive.



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