Monday, 22 February 2016

pharmacology - Why does Penicillin only affect bacterial cell walls


I was quite fascinated by the feature Should Science Pull the Trigger on Antiviral Drugs—That Can Blast the Common Cold? in this month's Wired magazine.


They explain that Penicillin is effective at killing bacteria because it interferes with the growth of bacterial cell walls.


How does Penicillin do that exactly? And why does it not dissolve human cells as well?



Answer



Bacteria have a mesh-like structure surrounding their plasma membrane called a cell wall. The cell wall is made up of peptidoglycan polymers that form a rigid crystalline structure that helps protect the osmotic pressure of the bacterial cytoplasm.



Penicillin and other β-lactams work by inhibiting the final step of peptidoglycan synthesis, which prevents transpeptidation (crosslinking) of the peptidoglycan molecules. This leads to the death of the bacterium by osmotic pressure due to the loss of the cell wall.


This drug doesn't affect human cells because they lack a cell wall surrounding their plasma membrane.


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