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I recently read that penicillin works by damaging the peptidoglycan layers of a bacterial cell wall causing osmotic lysis, which is when the bacteria cell bursts due to osmotic pressure.

I just would like to know how peptidoglycan prevents this. Thanks for any responses!

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marked as duplicate by anongoodnurse, AliceD, March Ho, James, rg255 Jun 3 '16 at 5:36

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Peptidoglycan is formed by the linkage of molecules of NAM ( N-acetylmuramic acid) and NAG (N-acetylglucosamine) into a polysaccharide structure. Many of these structures are then formed into a lattice by crossbridges of polypeptides. In gram + bacterial cell walls many layers of this lattice are stacked up forming a rigid structure, that is external to the plasma membrane, and provides more resistance to osmotic lysis than the plasma membrane alone posesses.

Penicillin interferes with the final linking of the peptide crossbridges which results in a weaker cell wall that will make it more likely that the cell will undergo osmotic lysis.

Gram - bacterial cell walls are quite different than gram + cell walls. They do contain peptidoglycan but the peptidoglycan layer is thinner - only one, or very few, layers of peptidoglycan with some structural differences also. Therefore, gram - bacterial cell walls are weaker than gram + bacterial cell walls.

"Microbiology, an introduction" Tortora, Funke and Case 11th EDition pp 84-86

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The bacterium always has a higher internal osmotic pressure (they contain a lot of stuff, and most of the time much more stuff than their surroundings). This pressure is contained by the membrane and cell wall, and when you destroy the cell wall the membrane alone is not strong enough, and the bacterium will spill its guts.

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