Penicillin

• Which fungus makes penicillin?

  Penicillium
• How does penicillin enter gram positive and gram negative cells?

  Positive: diffuses into the cell wall

  Negative: enters through molecules called porins, which form pores in the outer lipopolysaccharide layer
• What do bacteria continually do to their cell wall?

  Bacteria continually make and break down their cell wall
• What is the function of DD-transpeptidase?

  It catalyses condensation reactions that make cross links between amino acid side chains joining peptidoglycan molecules
• Why is DD-transpeptidase also known as PBP?


  Penicillin-binding protein: because penicillin binds to it, acting as an enzyme inhibitor
• How does penicillin affect cell wall formation?

  Penicillin is an enzyme inhibitor, so cross links are not reformed by DD-transpeptidase. It affects breakdown by hydrolysis, so more cell wall is lost than gained. No peptide cross links are made, so precursor molecules build up which are also hydrolysed, and this weakens the cell wall
• How is penicillin bactericidal?

  It kills the bacteria as it weakens the cell wall. Water moves in by osmosis, and the cell wall cannot withstand the pressure, so it bursts