Lecture 7 Better Antibiotics.docx

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University of Auckland
Biological Sciences
Ken Scott

Lecture 7 Better Antibiotics Friday, 28 September 2012 10:15 p.m. Salvarsan:  Arsenic derivative  Compound 606  Kills bacteria that cause syphilis  specific against treponemia pallidum Antibacterial acting on bacterial wall:  β lactam antibiotics -penicillin  successful, non toxic because humans do not have equivalent to cell wall so not effected by inhibitor. bacteria can produce B-lactamase that can combat B lactams antibiotic effect  Penicillin attacking cell wall :  Cell wall contains polymer of 2 monomer units NAM and NAG and B-1,4 linkages between NAM and NAG  D amino acids present, not present in humans, this is targeted by penicillin.  Affects the assembly of the cell wall causing the bacteria to become osmotically unstable causing the cell to burst and die.  This is due to the O=C-N bond in the beta lactam ring. this interferes with cell wall protein formation.  different R groups for different types of penicillin.  Inhibits transpeptidase preventing crosslinks from forming  terminal D-ala-D-ala peptide bond broken - new peptide bond formed between COOH of D-ala and NH2 of glycine  The C-N of penicillin is a structural analogue of the peptide bond Park nucleotides:  Park nucleotides are the units released when the bacterial cell lyses. Remnants of the cell wall structure.  UTP acts as the carrier for the assembly of glycoproteins that form the bacterial cell wall.  UDP-NAM  UDP-NAG  UDP-NAM-peptide-NAG  P acts as a carrier for polypeptide glycan synthesis  Chain of glycine's can be linked to amino or carbon groups  found in cell walls (peptide glycan's) B-lactamase:  Enzyme produced by bacteria as a resistance to B-lactam  Resistance to penicillin by hydrolysing the b-lactam bond preventing disruption of the cross links.  the use of different penicillin variants may help as some are less susceptible to B-lactamase  Cephalosporins usually have a resistance to B-lactamase  The biochemical action of B-lactamase: hydrolyses C-N bond creating COOH and NH2+ making penicillin inactive. Clarulanic Acid:  B lactam compound  Non antibiotic, inhibits
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