What are glycans?

Hint: Polysaccharides or the carbohydrate portions such as glycoprotein, glycolipid, or the portion of carbohydrate which contain oligosaccharides. These are vital for the various biological processes.

Complete step by step answer:
The compounds which contain a large number of monosaccharides linked together by a glycosidic bond are called polysaccharides. Glycan is the synonym for polysaccharides. The portion of carbohydrates such as glycoprotein, glycolipid, proteoglycan, or even if the carbohydrate contains oligosaccharide is also called glycan.

Additional information:
- Glycan is an IUPAC synonym for polysaccharides.
- O- glycosidic linkage of monosaccharides are present in glycans
- For example, cellulose consists of β- 1,4- linked D-glucose, and chitin consists of β- 1,4- linked N-acetyl-D-glucosamine so they are called glycans. If cellulose they are more specifically considered as glucans
- They can be homo or heteropolymers of monosaccharide residues
- Glycans can be linear or branched.
- In glycoproteins and proteoglycans glycans can be seen attached to proteins.
- Generally, they are found on the surface of cells.
- O-linked glycans and N- linked glycans are more commonly found in eukaryotes but are less commonly found in prokaryotes.
- N-linked glycans In eukaryotes are derived from a core 14-sugar unit and they are assembled in the cytoplasm and endoplasmic reticulum.
- For proper protein folding in eukaryotic cells, N-linked glycans are extremely important.
- N-linked glycans help in dictating the migration pattern of the cell in the immune system
- In the development of intestinal microflora, O-linked glycans such as mucus have an important role.

Note: Examples of O-linked glycoproteins are: Glycophorin (a protein in cell membranes of erythrocytes), Mucin (a protein in saliva), Notch (a transmembrane receptor involved in the development and cell fate decisions), Thrombospondin, Factor VII, Factor IX. Glycosaminoglycans are another type of glycans. Ex: heparin, heparan sulfate, dermatan sulfate, Keratan sulfate, chondroitin.