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2.6.3. Heterosides


The  glycoside  is formed by the union of a sugar molecule with another non - carbohydrate, we call aglycone.

The main types of association between carbohydrates and other types of molecules are:


The peptidoglycan or murein are polymers of N-acetylglucosamine (NAG) and N-acetylmuramic (NAM) joined by β (1→4) linked to chains of amino acids short. They are part of the bacterial wall.


The proteoglycans are molecules made up of a large fraction of polysaccharide (80% of the molecule), called glycosaminoglycan, and a small protein fraction (approximately 20%).

Glycosaminoglycan chains are made up of linear polymers of N-acetylglucosamine (or N-acetylgalactosamine) and glucuronic acid. The most common are:

  • The hyaluronic acid (in connective tissue, vitreous humor or synovial fluids).
  • The chondroitin sulfate (woven bone and cartilage).
  • The heparin (anticoagulant in lung, liver and skin).


The glycoproteins are molecules formed by a small carbohydrate fraction (between 5% and 40%) and a protein fraction, which are joined by strong bonds (covalent).

They differ from proteoglycans in that the carbohydrate part contains neither hyaluronic acid nor chondroitin sulfates.

The main ones are: secretory mucins, such as salivary ones; the glycoproteins of blood, such as prothrombin and immunoglobulins; the gonadotropic hormones; some ribonuclease enzymes and the so-called glycoproteins of cell membranes.


The glycolipid consist of monosaccharides or oligosaccharides bound to lipids (ceramide). They are generally found in the cell membrane. The best known are:

  • The cerebrosides are glycolipids in which ceramide is attached to a monosaccharide or an oligosaccharide.
  • The gangliosides are glycolipids in which ceramide binds to an oligosaccharide complex that always appears sialic acid.