Peptidoglycan is a mesh of linked sugar chains cross-linked by short chains of amino acids in the cell walls of most bacteria. Its absence from the cell walls of archaea helps distinguish envelope chemistry without confusing either cell wall with a cell membrane. See OpenStax Microbiology, 3.3: cell walls and peptidoglycan.
Forms the bacterial cell wall.
From the Wikipedia image we can see clearly the polymer structure formed: it is a mesh with:
- sugar covalent bond chains in one direction. These have two types of monosaccharide, NAM and NAG
- peptide chains on the other, and only coming off from NAM
Peptidoglycan polymer structure
. Source. 
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