Chem167_L18_Jun4_final

E bacteria can acquire resistance important wrt

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Unformatted text preview: is Penicillin can be seen to mimic acyl- D- Ala- D- Ala R C H N R H H S C Me O H N Me H H N O N Me O CH3 O CO2H Penicillin H CO2H Acyl- D- Ala- D- Ala R C But 6- methylpenicillin is inac#ve despite being a closer analogue H N Me H S O N O Me Me CO2H Mechanism of ac#on - bacterial cell wall synthesis Alternate hypothesis: Penicillin may act as an ‘umbrella’ inhibitor of transpep#dase D - A l a - D - A l a R C H N Blocked H S Me R O N O HO C Me CO2H H Ac#ve Site OH Acyla#on H N H S Me O O HN O Me CO2H OH Gram +ve and Gram - ve Cell Walls • Penicillins have to cross the bacterial cell wall in order to reach their target enzyme • Cell walls are porous and are not a barrier • The cell walls of Gram +ve bacteria are thicker than Gram - ve cell walls, but the former are more suscep#ble to penicillins Gram +ve and Gram - ve Cell Walls Gram +ve bacteria Thick porous cell wall Cell membrane Cell • Thick cell wall • No outer membrane • More suscep#ble to penicillins Gram +ve and Gram - ve Cell Walls Gram - ve bacteria Hydrophobic barrier Outer membrane Porin Lactamase enzymes L L L Periplasmic space Cell membrane Thin cell wall L Cell • Thin cell wall • Hydrophobic outer membrane • More resistant to penicillins Problems with Penicillin G • It is sensi#ve to stomach acids • It is sensi#ve to β- lactamases - enzymes which hydrolyse the β- lactam ring •  It has a limited range of ac#vity Problem 2 - Sensi#vity to β- Lactamases β- Lactamases • Enzymes that inac#vate penicillins by opening β- lactam rings...
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