Question

explain why a lipid, dolichol, is involved in glycoprotein synthesis.

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Answer 1

Ans.

• Proteins in which olygosaccharide chains are covalently linked to amino acid side chains are known as glycoproteins.
• Attachement of carbohydrates to proteins occur during co-translational or post-translational modifications, a process refered as glycosylation.
• Glycoproteins play a key role in the cell-cell interactions by acting as an important integral membrane proteins.
• Dolichols are any cluster of a long chain (mostly unsaturated) organic compounds build up of different numbers of isoprene subdivisions.
• These isoprene units terminate in an alpha saturated group of isoprenoid which contain an alcoholic functional group.
• Major component of substantia nigra neuromelanin are dolichols.
• Dolichol, as dolichol phosphate, carry out N-glycosylation, a co-translational modification process of proteins.
• In the formation of carbohydrate chains of N-linked glycoproteins, dolichols plays the role of saccharide carrier.
• In the formation of the oligosaccharide Glc3-Man9-GlcNAc2, dolichol plays a key role as a membrane anchor.
• Then, the transfer of this oligosaccharide from the donor (dolichol) onto the asparagine residues of freshly made polypeptide chains (reciever) takes place.
• Passing of monosaccharides to the constructing Glc3-Man9-GlcNAc2-Dolichol carrier also takes place in the presence of dolichol.
• Also, during posttranslational modifications, dolichols can be attached to proteins forming a large glycoprotein in the rough E.R.