Chondroitin, a glucosaminoglycan (GAG), is a polysaccharide chain of alternating units of N-acetylgalactosamine (GalNAc) and glucuronic acid (GlcA) that can be sulfated on the either or both GalNAc and GlcA units. Chondroitin and its sulfates are frequently attached to proteins to form proteoglycans.