PEPTIDOGLYCAN
Peptidoglycan consists of carbohydrate backbone (glycan chain) composed of alternating units of N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG) molecules. Glycan chains are connected by short peptides.Attached to each of the muramic acid molecules are a tetrapeptide consisting of both D- and L- amino acids, the precise composition of which differs between bacteria. Teichoic acid and lipoteichoic acid which are polymers of a sugar alcohol (ribitol or glycerol) are embedded in it.
Special Amino Acids Found in Peptidoglycan Layer:
➧ Diaminopimelic acid: Unique to bacterial cells.
➧ D- alanine: Involved in the cross links between tetrapeptides and in the action of penicillin.
Functions of Peptidoglycan Layer
- It provides rigid support to bacterial cells and maintains the characteristic shape of the cell.
- Allows bacterial cell to withstand media of low osmotic pressure, such as water.
- Peptidoglycan is a good target for antibacterial drugs. Eg. Penicillins, cephalosporins etc inhibit transpeptidase reaction which makes cross-links between the two adjacent tetrapeptides.
- Lysozyme enzyme present in human tears, mucus, and saliva cleave peptidoglycan backbone breaking its glycosyl bonds.
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