Question #110fa
1 Answer
See below.
Explanation:
A peptidoglycan is a cross-linked polymer of sugars and pentapeptides that makes up the cell walls of all bacteria.
How antibiotics affect peptidoglycans
Antibiotics affect peptidoglycans:
- by binding to transpeptidase enzymes
- by binding to the pentapeptide of peptidoglycan monomers
- by binding to the transporter bactoprenols
The construction and repair of the peptidoglycan involves four steps:
- Various autolysin enzymes break the glycoside and peptide linkages.
- Protein carrier molecules called bactoprenols transport the monomers to the ends of the growing peptidoglycan chains.
- Transglycosylase enzymes insert monomers into the wall.
- Transpeptidase enzymes re-form the peptide cross-links between the layers
Binding to Transpeptidase Enzymes
Drugs like penicillin mimic the D-Ala-D-Ala groups at the end of the pentapeptide.
They bind to the transpeptidase and prevent the re-forming of the cross-links between chains.
This leads to weakening of the cell wall and its rupture by osmotic pressure.
Binding to the Pentapeptide
Antibiotics like vancomycin form strong H-bonds to the terminal D-Ala-D-Ala groups of the pentapeptide.
This prevents the transpeptidases from forming the peptide cross-links between the rows and layers of peptidoglycan.
The result is a weak cell wall and subsequent osmotic lysis of the bacterium.
Binding to Bactoprenol
Antibiotics like bacitracin bind to the bactoprenols and prevent them from transporting new monomers.
As the autolysins continue to break the peptide cross-links but new cross-links fail to form, the bacterium bursts from osmotic lysis.
The video below explains the formation of a peptidoglycan and the action of penicillin on it.
