Structure of the Repeating Unit in Peptidoglycan These constituents are connected to form a repeating structure, the glycan tetrapeptide. Peptidoglycan is composed of two sugar derivatives, N￾acetylglucosamine (NAG) and N-acetylmuramic acid (NAM), and a small group of amino acids consisting of L-alanine, D-alanine, D-glutamic acid, and either lysine or diaminopimelic acid (DAP).Structure of the Repeating Unit in Peptidoglycan These constituents are connected to form a repeating structure, the glycan tetrapeptide. Peptidoglycan is composed of two sugar derivatives, N￾acetylglucosamine (NAG) and N-acetylmuramic acid (NAM), and a small group of amino acids consisting of L-alanine, D-alanine, D-glutamic acid, and either lysine or diaminopimelic acid (DAP)