What are the main building blocks of peptidoglycan?

Amino sugars and tetrapeptides form the building blocks of peptidoglycan. Each peptidoglycan molecule consists of two amino sugars, N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). These molecules are alternated in long chains and cross-linked to one another by a tetrapeptide coming off the NAM sugar. Interlocking chains of identical peptidoglycan monomers form a vast polymer that makes up the peptidoglycan layer, which surrounds the outside of the cytoplasmic membrane of bacterial cell walls.