Peptidoglycan
Peptidoglycan, also known as murein, is a homogenous layer lying outside the plasma membrane in prokaryotes. The peptidoglycan layer is thicker in Gram-positive bacteria (20 to 80 nm) than in Gram-negative bacteria (7 to 8 nm). It forms around 90% and 10% of dry weight of gram positive and gram negative bacteria respectively.
Chemical structure
The peptidoglycan layer in the bacterial cell wall is a lattice structure formed from linear chains of two alternating amino sugars, namely N-acetyl glucosamine (GlcNAc) and N-acetyl muramic acid (MurNAc). Each MurNAc is attached to a short (5 residues) amino acid chain. Cross links between amino acids in different linear amino sugar chains result in a 2-dimensional sheet that is strong and rigid. The exact amino acid sequence and the exact overall structure vary with the bacterial species.
Biological purpose
Peptidoglycan layer serves a structural role, giving bacterial cell walls their shape and strength and counteracting the osmotic pressure of the cytoplasm. It is also involved in binary fission of the bacterial cell.
