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

Classification of glycoproteins

Glycoproteins result from the covalent association of carbohydrate moieties with protein. The amino acids and carbohydrates comprising the glycoprotein molecules are organised in two general ways. One type has a protein core, frequently molecular weight less than 100,000 to which are attached a few oligosaccharides residues.

The other type has a much higher molecular weight and is mainly carbohydrate in content and is organised as hundreds of small oligosaccharides residues covalently linked to a peptide core.

Classifications of glycoproteins is based in the type of glycosidic linkage involved in the attachment of carbohydrate to the peptide backbone.
*Glycoproteins having one carbohydrate group in each protein group
Ovalbumin MW 44.5x1000
Soybean hemagglutinin MW 110x1000
Ceruloplasmin MW 143x1000
Transferrin MW 92x1000

*Glycoproteins having a few carbohydrates groups in each protein unit
Ovomucoid MW 28x1000
Fibrinogen MW 330x1000
Fetuin MW 46x1000
D-glucose oxidase MW 186x1000
Thyroglobulin MW 600x1000

*Glycoproteins having many carbohydrate groups in each protein unit
Epithelial mucins MW 1000x1000
Blood group substance A MW 416x1000
Classification of glycoproteins

What are the different types of fat in food?

Fats and oil can undergo detrimental flavor changes as a result of two major types of deterioration, oxidation at the double bonds in unsaturated fatty acids and hydrolysis at the ester linkage.

High intakes of fat are linked to health problems and can lead to obesity (overweight). Fats are concentrated sources of energy and many fats contain vitamins A and D which are important for good health. Fats in the body include those consumed in the diet and those produced from carbohydrates and proteins.

There are four main types of fat are saturates, monounsaturates, polyunsaturates and transfats.

Saturated fat
Fats that contain no double bonds are referred to as saturated fats. Saturated fat may raise blood cholesterol levels which may cause heart disease. It is necessary for proper bone development and for the prevention of osteoporosis.

Saturated fats also support the immune system and help keep the human healthy.

Saturated fats are found in meat products such as pies and sausages, dairy produce and cakes and biscuits’ made from hydrogenated vegetable oil or butter.

Monounsaturates
Fats containing some double bonds are known as unsaturated fats – those with one double bond are mono-unsaturated. Monounsaturates are not associated with heart disease and are found in olive oil and rape seed oil.

Polyunsaturates
Fats with two or more double bonds are polyunsaturated. The more double-bonds in a fat, the more fluid it is, and it is this fluidity found in highly unsaturated fatty acids and that is so crucial in brain structure and function. Polyunsaturates lower blood cholesterol levels and are found in sunflower oil and soya oil.

Transfats
Transfats found in pastries, some margarine, fried foods and many snack and convenience foods.
What are the different types of fat in food?