structure and function of glycolipid.pptx

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1. STRUCTURE AND FUNCTIONS OF GLYCOLIPIDS - DAYANA.K

2. 1 . Cerebrosides ( Glycospingosides ) Occurrence Cerebrosides occur in large amounts in the white matter of brain and in myelin sheath of nerve . They are not found in embryonic brain but develops as medullation progress. In smaller amount they appear to be widely distributed in animal tissues . In medullated nerves the concentration of cerebrosides are much higher than in non- medullated nerve fibres .

3. Structure of cerebrosides The structure of cerebrosides contain a high molecular weight fatty acid , sphingosine, sugar usually galactose but sometimes glucose is attached. But it has no glycerol, no phosphoric acid and no nitrogeneous base. They have no electric charge since their polar head groups are neutral.

4. Ceramide The name ceramide is commonly used to designate the sphingosine and fatty acid(or N- acylsphingosine ) portion of the cerebrosides . Here the sphingosine carries the galactose by glycosidic linkage on primary alcohol group and the fatty acid by an amide linkage. Psychosin By prolonged hydrolysis of any cerebroside with Ba(OH)2, FA is removed and it yields psychosin (sphingosine+ sugar). Psy cho sin can be further hydrolysed to yield sphingosine and galactose.

5. Types of cerebrosides Individual cerebrosides are differentiated on the basis of fatty acid component. Four types of cerebrosides have been isolated. (a) Kerasin - contains saturated C24 lignoceric acid. (b) phrenosin ( cerebron )- contain 2-hydroxyl derivative of lignoceric acid called cerebronic acid. (c) Nervon - contains an unsaturated homologue of lignoceric acid called nervonic acid. (d) Oxynervon - contains a 2-hydroxyl derivative nervonic acid called oxynevonic acid.

6. Clinical aspect of cerebrosides Gaucher’s Disease An inherited disorder of cerebrosides metabolism ( lipidosis ). Inheritance: It is autosomal recessive Enzyme defect : Deficiency of the enzyme beta gluco-cerebrosidase . In absence of the enzyme the cerebroside cannot be degraded i n the body as a result large amount of glucocerebroside accumulate in liver, spleen, bone marrow and brain.

7. 2. Gangliosides Occurrence In 1955, Klenk isolated a new type of glycolipid from brain tissue and named it as ganglioside. These are found in ganglion cell of nervous tissue and in parenchymatous tissues like spleen and erythrocytes. They make up about 6% of membrane lipids in the gr e y matter of the brain. They are also found in lesser amounts in membrane of non neural tissue. Gangliosides acts as receptor for toxic reagents like pathogens Vibrio cholera influenza virus and tetanus toxin. It play a role in cell-cell interaction.

8. Structure of gangliosides The structure of ganglioside contain a ceramide (N- acylsphingosine ) linked to 2 additional mole of carbohydrate, 1 mole of N- acetylgalactosamine and 1 to 5 mole of N- acetylneuraminic acid (NANA). Types of gangliosides : More than 15 different gangliosides have been determined. These are abbreviated by the letter G with subscript M, D or T to designate they contain one, two or three sialic acid and NANA residues and a number or letter to distinguish different members of a group from one another. In essence they consist of oligosaccharide chain attached to ceramide(N- acylsphingosine by a sugar residue usually glucose. They lack phosphoric acid. Four important types are: GM-1, GM-2, GM-3 and GD-3 .

9. Clinical aspect of Gangliosides Tay- sachs Disease Inheri tan ce : Autosomal recessive Enzyme defect : N- acetylgalactosaminidase Accumulation of gangliosides in brain and nervous system. The symptoms are mental retardation, difficulty in eating, Cherry red spot in retina and blindness .

10. 3. Sul fo lipids Occurrence Lipid material containing sulphur present in various tissue found in liver, kidney, testes, brain and certain tumours . Most abundant in white matter of brain . Several types of sulphur containing lipids have been isolated from brain and other tissues. This glycolipid is widely distributed in plants . It is localized in chloroplast and also found in chromatophores of photosynthetic bacteria.

11. Structure of sulfolipids The sulfur in this compound present as a sulfonic group in a hexose molecule, this may be included under a class of compound called sulfolipids .

12. 4. Sulfatides A sulfate ester analogue of phrenosin . It is abundant in white matter of brain. It is another sulphur - containing glycolipid. The sulfate is present in ester linkage at C3 of the galactose portion of the molecule. Members of this group of cerebroside sulphuric esters have been designated as sulfatides .

13. Functions of glycolipid It provides energy to the cells. It is an essential part of cell membranes. It helps in determining the blood group of an individual. It acts as receptors at the surface of the red blood cells. It also functions by assisting the immune system by destroying and eliminating the pathogen from the body.

14. References Fundamentals of Biochemistry Book – J.L JAIN, SUNJAY JAIN, NITIN JAIN Textbook of Medical Biochemistry – MN Chatterjea, Rana Shinde