24. Which one of the following glycosaminoglycans is generally NOT covalently attached to protein as proteoglycans?
(1) Chondroitin sulphate                         (2) Dermatan sulphate
(3) Heparan sulphate                             (4) Hyaluronan

Overview: Glycosaminoglycans and Proteoglycans

Glycosaminoglycans (GAGs) are long, unbranched polysaccharides consisting of repeating disaccharide units. Proteoglycans are proteins with one or more GAG chains covalently attached. Proteoglycans contribute to the extracellular matrix’s structure and function by forming hydrated gels, providing mechanical support and mediating cellular signaling.​

Hyaluronan’s Unique Status

• Hyaluronan is synthesized at the plasma membrane as a large, non-sulfated GAG.

• Unlike other GAGs, it exists as a free polysaccharide, not attached to a core protein.​

• It forms large hydrated networks in extracellular spaces, contributing to tissue hydration and elasticity.

Other Glycosaminoglycans

• Chondroitin sulphate: Covalently attached to core proteins forming proteoglycans.

• Dermatan sulphate: Similar to chondroitin sulfate, forms proteoglycans.

• Heparan sulphate: Attached to proteins forming proteoglycans involved in cell signaling and matrix interactions.

Table: Glycosaminoglycan Attachment Status

Conclusion

Hyaluronan is the exceptional glycosaminoglycan that does not covalently link to core proteins to form proteoglycans, in contrast to other GAGs like chondroitin sulfate, dermatan sulfate, and heparan sulfate. This property gives hyaluronan unique structural and functional roles in the extracellular matri