Penicillin Flashcards
Who discovered penicillin?
Alexander Fleming
How does penicillin work?
Penicillin inhibits the final stage of cell wall synthesis by irreversibly inhibiting transpeptidase enzyme
What is transpeptidase enzyme responsible for?
Formation of peptidoglycan cross-links
Why are gram-negative cells not susceptible to penicillin?
Walls have a strong barrier which prevents hydrophilic penicillin molecules passing through so penicillin can only diffuse through pores
Why does penicillin resistance occur?
Bacteria are prone to genetic mutations and can form resistant strains
Bacterial transpeptidase enzyme may have a low affinity for penicillin
Bacteria may have efflux mechanisms which pump penicillin out of cells
What does the penicillinase enzyme do?
Destroys penicillin
How are penicillin G and penicillin V different?
Acyl side chains
Why is the acyl side chain different on penicillins?
Due to the carboxylic acid present in the fermentation medium
What are the key groups on penicillin?
Bicyclic ring system
Carboxylic function
Amine bond to attach acyl chain
What shape is penicillin G?
Envelope shape
Why is the amide bond on penicillin G unstable?
N’s lone pair cannot delocalise
High degree of angular strain due to 4 membered ring
Why is penicillin G injected?
It is not orally available
How can penicillin G be developed?
Increase acyl group size to make lactam ring less accessible - increasing resistance to B-lactamase
Increase the chemical stability for oral administration
What can be varied on penicillin?
Variation is limited to the acyl side chain
What structures on penicillin G are involved in bonding?
Amide and carboxylic acid (as carboxylate ion)
