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[Biochemistry](https://durgical.com/en/biochemistry/) · Topic

# Glycosaminoglycans (mucopolysaccharides)

Glycosaminoglycans are long, negatively charged sugar chains that hold water and give bulk and toughness to cartilage and connective tissue.

Updated 2026-11-01

## Key facts

- Unbranched chains of repeating disaccharides: an amino sugar (glucosamine or galactosamine) + a uronic acid (glucuronic or iduronic) or galactose.
- Strongly negative (sulfates and carboxyls): they attract Na⁺ and water and form gels that resist compression.
- Types: hyaluronic acid (no sulfate, no protein), chondroitin sulfate (cartilage), dermatan sulfate (skin, valves), heparan sulfate (basement membranes), heparin (mast cells) and keratan sulfate (cornea, cartilage).
- Except hyaluronan, they attach to a core protein (proteoglycan), such as cartilage aggrecan.
- They are broken down in lysosomes; defects cause the mucopolysaccharidoses, with dermatan and heparan sulfate in urine.

## In detail

- 1. Synthesis takes place in the ER and Golgi: sugars arrive as UDP-sugars (UDP-glucuronate comes from UDP-glucose).
- 2. The chain is anchored to a serine of the core protein through a linker tetrasaccharide (xylose-galactose-galactose-glucuronic acid).
- 3. Once built, the chain is modified: sulfation and epimerisation of glucuronate to iduronate.
- 4. Hyaluronan is made differently: at the plasma membrane, with no core protein, and it can reach millions of daltons.
- 5. In the lysosome, exo-enzymes remove one sugar or sulfate at a time from the end; if one is missing, breakdown stops there.
- 6. Roles: joint and vitreous lubrication (hyaluronan), cartilage toughness (aggrecan), the glomerular basement membrane filter (heparan sulfate) and anticoagulation (heparin with antithrombin).

**Also called**
GAGs, Mucopolysaccharides, Proteoglycans

## Clinical notes

- Mucopolysaccharidoses: coarse facial features, hepatosplenomegaly, dysostosis multiplex, stiff joints, valve disease and, in some, corneal clouding or cognitive decline.
- MPS I (Hurler) and II (Hunter) store dermatan and heparan sulfate; Hunter does not cause corneal clouding.
- Heparin uses its negative charge to bind antithrombin and speed up the inhibition of thrombin and factor Xa.

## Related conditions

- [Hurler syndrome (mucopolysaccharidosis type I)](https://durgical.com/en/conditions/hurler-syndrome/)
- [Hunter syndrome (mucopolysaccharidosis type II)](https://durgical.com/en/conditions/hunter-syndrome/)
- [I-cell disease (mucolipidosis II)](https://durgical.com/en/conditions/i-cell-disease/)
- [Knee Osteoarthritis](https://durgical.com/en/conditions/knee-osteoarthritis/)

## Related

- [Hyaluronic acid (hyaluronan)](https://durgical.com/en/biochemistry/molecules/hyaluronic-acid/)
- [α-L-Iduronidase](https://durgical.com/en/biochemistry/enzymes/l-iduronidase/)
- [Carbohydrate chemistry](https://durgical.com/en/biochemistry/topics/carbohydrate-chemistry/)
- [Lysosomal storage diseases](https://durgical.com/en/biochemistry/topics/lysosomal-storage-diseases/)
- [UDP-glucose](https://durgical.com/en/biochemistry/molecules/udp-glucose/)

## Test yourself

Think of the answer, then tap the question to see it.

## Why do glycosaminoglycans form gels that resist compression?

Their negative charges attract cations and water; the hydrated chain fills a large volume and resists being squeezed.

## Which GAG has no sulfate and no core protein?

Hyaluronic acid (hyaluronan).

## Which GAGs appear in the urine in MPS I and II?

Dermatan sulfate and heparan sulfate.

## Which sugar distinguishes dermatan sulfate from chondroitin sulfate?

Iduronic acid, formed by epimerisation of glucuronic acid.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/biochemistry/topics/glycosaminoglycans/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Glycosaminoglycan metabolism](https://reactome.org/PathwayBrowser/#/R-HSA-1630316) (Reactome, 2026); [Heparan sulfate/heparin (HS-GAG) metabolism](https://reactome.org/PathwayBrowser/#/R-HSA-1638091) (Reactome, 2026); [Chondroitin sulfate/dermatan sulfate metabolism](https://reactome.org/PathwayBrowser/#/R-HSA-1793185) (Reactome, 2026); [Hyaluronan metabolism](https://reactome.org/PathwayBrowser/#/R-HSA-2142845) (Reactome, 2026); [MPS I - Hurler syndrome (HS-GAG degradation)](https://reactome.org/PathwayBrowser/#/R-HSA-2206302) (Reactome, 2026); [Chondroitin Sulfate (CID 24766)](https://pubchem.ncbi.nlm.nih.gov/compound/24766) (PubChem, NCBI, 2026) · Public domain; Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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