This pathway describes the biosynthesis and degradation of amino sugars, glycosaminoglycans or mucopolysaccharides. Glycosaminoglycans (GAGs) or mucopolysaccharides are long unbranched polysaccharides consisting of a repeating disaccharide unit. Members of the glycosaminoglycan family vary in the type of hexosamine, hexose or hexuronic acid unit they contain (e.g. glucuronic acid, iduronic acid, galactose, galactosamine, glucosamine). In this pathway the fates of three types of amino sugars (neuraminate, mannosamine and glucosamines) are depicted. The central hub metabolite to this pathway is UDP-N-acetyl-D-glucosamine. This molecule can either serve as a precursor to polymeric mucopolysaccharides, a precursor to other types of amino sugars, or a precursor to fructose 6-phosphate, which can be used in fructose/mannose metabolism.