Glycolipids: Part of family glycoconjugates

Glycolipids were discovered and named by Ernst Klenk after their isolation from brain tissue in 1942.

Glycolipids are glycosyl derivatives of lipids. They are collectively a part of a larger family of substances known as glycoconjugates. These are molecules in the cell surface that chains of carbohydrates bind to. In addition to glycolipids, other major types of glycoconjugates includes glycoproteins, glycopeptides, peptidoglycans, proteoglycans and lipopolysaccharides.

The term glycolipids, in general, encompasses a wide diversity of structurally heterogeneous biological compounds that are produced by microbes, plants, animals and humans. The lipid potion of glycolipids is ceramide, which consist of fatty acids of varying lengths that bind to a long chain of aliphatic amino alcohol called sphingosine.

The IUPAC uses the term GLs to broadly designate any compound containing one or more monosaccharide residues bound by glycosidic linkage to a hydrophobic moiety.

Glycolipids are classified as follows:
* Glycoglycerolipids
The term glycoglycerolipid is used to designate glycolipids containing one or more glycerol residues.
* Glycosphingolipids
The term glycosphingolipid designates lipids containing at least one monosaccharide residue and either a sphingoid or a ceramide. 

The glycosphingolipids can be subdivided as follows:
1.Neutral glycosphingolipids,
2.Acidic glycosphingolipids

Most of the glycolipids are distributed in membranous structures in the cell. Two-thirds of the total glycolipids are distributed in intracellular membranes such as golgi apparatus, endosomes, lysosomes, nuclear membrane, endoplasmic reticulum, and mitochondria.
Glycolipids: Part of family glycoconjugates

What is glycoprotein?

Glycoproteins may be defined as biopolymers having amino acids and sugar reduces link covalently to each other. They are widely distributed in nature. Found in higher animals, plants and microorganisms, glycoproteins contain a protein chain of any of the 20 naturally occurring L- α -amino acid units.

Proteoglycans are a subclass of glycoproteins with distinctive structure. Glycoproteins differ from monosaccharides protein structures in that they contain considerably less carbohydrate.

The mucopolysaccharides however may be considered a type of glycoprotein. Formed in the Golgi apparatus in the process of glycosylation, glycoproteins are important components of plasma membranes in which they extend throughout the lipid layer.

The molecular weights of glycoprotein range from 15,000 up to million. Some glycoproteins have only one glycochain in a molecule, whereas other glycoprotein possesses many glycochains in a molecule. The carbohydrate chains of glycoproteins are short, consisting perhaps eighth to ten saccharides units.

D-galactose, N-acetyl-D-galactosamine, D-glucose,  N-acetyl-D-glucosamine, D-mannose, L-fucose, and sialic acid, comprise the bulk of the carbohydrate moiety.
What is glycoprotein?

Classification of Lipids

Classification of Lipids
Lipids include all substances that are extractable from biological materials with the usual fat solvents (ether, chloroform, benzene, carbon tetrachloride, acetone, etc). Certain lipids are an energy source for the cell, others are structural compounds (particularly important are the lipid constituents of cell and organelle membranes), and still other function as hormones. This diversity of function recalls the not too remote past when lipids were considered to be inert constituents of adipose cells.

Of the many compounds classified as lipids, only fraction is significant in the diet, or in the structure and function of the human cell. The following classification is limited to lipids of importance in animal nutrition and excludes the fat soluble vitamins that, although properly classified as lipids, following the classic practice of nutritionist.

A. Simple Lipids
Fatty acids
Neutral fats (mono-, di- and triacyl glycerols)
Wax
*Sterol ester
*Nonsterol ester

B. Compound Lipids
Phospholipids
*Phosphatidic acids, lecithin, cephalins, etc
*Plasmalogens
*Sphinghomyelins
Glycolipid (carbohydrate containing)
Lipoproteins (lipids in combination with protein)

C. Derived Lipids, alcohol (including sterols and hydrocarbons)
Classification of Lipids