Break the peptide crosslinks in mature peptidoglycan

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break the peptide crosslinks in mature peptidoglycan Lytic transglycosylases break the β(1,4) linkages between NAG and NAM (example is lysozyme) Functional redundancy = several enzymes perform each reaction
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If cells are in hypotonic medium when PG is disrupted, they will lyse due to osmotic pressure If cells are in isotonic medium when PG is disrupted, the IM stays intact, and protoplasts are formed Peptidoglycan sacculus retains its shape after cell lysis, but PG is NOT a static structure. Over 50% of PG is recycled during each generation! PG protects bacteria against osmotic lysis
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Penicillin blocks the transpeptidation step of PG synthesis n normal transpeptidation, 1) A serine residue on the PBP orms a covalent intermediate with a pentapeptide, releasing free D-ala. 2) The PBP-D-ala intermediate s attacked by the NH 2 group of DAP on a neighboring peptide o form a crosslink and release he PBP enzyme. 1 2 D-ala D-ala
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Penicillin is a β-lactam antibiotic Different β-lactams contain different chemical groups in the R position
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Penicillin blocks transpeptidation It mimics the D-ala-D-ala residues of PG peptides and is attacked as a substrate β-lactam ring is broken during attack by the PBP, forming an irreversible intermediate with the PBP PBP protein Attacking Ser residue
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In growing cells, PG is continuously synthesized and broken down.
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