Hyaluronic acid is classified as which type of molecule?

• A. GAG
• B. Proteoglycan
• C. Both A and B
• D. None of the above

Answer: (A)

Hyaluronic acid is a glycosaminoglycan (GAG). GAGs are long, unbranched polysaccharides composed of repeating disaccharide units, often sulfated, and they typically form part of proteoglycans when attached to a protein core. Hyaluronic acid, specifically, is a repeating disaccharide of D-glucuronic acid and N-acetyl-D-glucosamine, and it is not sulfated nor covalently attached to a core protein. Proteoglycans are defined by having one or more GAG chains covalently linked to a protein core. Because hyaluronic acid lacks a protein core and is not covalently attached to protein, it is classified as a GAG. It can associate with proteoglycans to form large extracellular structures, but on its own it remains a GAG.