A macromolecule that is a component of the cell wall of bacteria; it is not found in eukaryotes. Consisting of chains of amino sugars (N-acetylglucosamine and N-acetylmuramic acid) linked to a tripeptide (of alanine, glutamic acid, and lysine or diaminopimelic acid), it confers strength and shape to the cell wall. Archaea possess a similar polysaccharide, pseudopeptidoglycan, with N-acetyltalosaminuronic acid instead of N-acetylmuramic acid.