GLCOLIPIDS(GLYCOSPHONGOLIPIDS) Ceramide+carbohydrate (glucose,galactose,oligosacchride side chain)=GLYCOLIPID Cerebrosides: contain a single moiety, principally galactose Sulfatides: sulfuric esters of galactocerebrosides Gangliosides: contain a complex oligosaccharide moiety

CEREBROSIDES. Ceramide+glucose or galactose(mostly) Occur in the white matter of the brain and in the myelin sheaths of the nerve fibres. There are different types of cerebrosides depending upon the differences in the type of the fatty acid and the monosacchride moiety. Examples;cerebron,nervon,oxynervon and kerasin.

Acommon fatty acid present in these compounds is 24 carbon containing fatty acid known as cerebronic acid. A more complex glycolipid is ceramide trihexoside,ceramide-glucose-galactose- galactose.

GANGLIOSIDES. Ceramide-glucose-galactose-N acetylgalactosamine-N acetylneuraminic acid(sialic acid) Gangliosides occur in brain spleen,RBCs and nerve cells. In the brain gangliosides contribute about 6%of the membrane lipids in the brain.

One important example of gangliosides is GM₁ It occurs in the itestinal cell membranes and acts as the site of attachment to cholera toxin. Its structure is ceramide-glucose-galactose-N | N-acetylneuraminic acid acetylgalactosamine-galactose

Globosiodes Closely related to glycolipids. Said to be mucolipids Ceramide-glucose-galactose-galactose-N- acetylgalactosamine

Clinical significance of sphingolipids RRRRRR Type 0 Type A Type B GlcNAc Fucose Galactose Sialic acid (NANA) Blood groups determined by various glycolipids on RBCs

SULPHOLIPID are sulfate esters of glycolipids.The sulfate group is esterified with the –OH group of the hexose moiety of molecule. Most abundant in the white matter of brain.

STEROIDS AND STEROLS A large number of compounds found in nature occuring in nonsponifiable fraction of lipids belong to class of compounds called steroids. Their parent nucleus is cyclopentanoperhydro- phenanthrene,which consists of four rings fused together and have total of 17 carbon.

Steroids with eight to ten carbon atoms in the side chain and a hydroxyl group at carbon no 3 are classified as sterols. Cholesterol is the major sterol in the animal tissues.others include ergosterol,bile acids,male and female sex hormones and hormones of adrenal cortex.Cardiac glycosides and some alkaloids also have steroid components.

CHOLESTEROL is the most abundant sterol. Normal plasma levels are from mg/dl. Structural component of cell membranes. In pecialized tissues cholesterol is precursor of bile acids, steroid hormones and vitamin D. The liver plays a central role in the regulation of body’s cholesterol homeostasis. Cholesterol enters into the liver cholesterol pool either through diet or by the denovo synthesis of cholesterol by extrahepatic tissues and liver it self.

Cholesterol is eliminated from the liver as unmodified cholesterol in the bile or it can be converted into bile salts that are secreted into the intestinal lumen. It can also serve as a component of plasma lipoproteins sent to the peripheral tissues. Imbalance between cholesterol eflux and influx leads to atherosclerosis and coronary artery diseases.

Cholesterol occurs both in free and bound form with fatty acids known as cholesteryl esters.Bound form is more hydrophobic.

Plant sterols such as sitosterol is poorly absorbed by humans. Plant sterols appear to block the absorption of dietary cholesterol. This has led to clinically useful dietary treatment for hypercholesteremia.Daily ingestion of plant steroid esters (in the form of commercially available trans fatty acid free margarine)is one of the dietary strategies leading to the reduction of plasma cholesterol levels.

7-DEHYDROCHOLESTEROL occurs mainly in skin.it is converted to vitamin D₃ when exposed to sunlight. ERGOSTEROL is a main sterol of fungi and yeast.when irradiated by ultraviolet rays,it is converted to vitamin D₂.

Lipoproteins Lipids must be transported to the various tissues to accomplish their metabolic functions. Because of their insolubility, they are transported in plasma in macromolecular complexes called Lipoproteins. Chemistry: Lipoproteins are spherical particles with non polar lipids (triglycerides and cholesterol esters) in their core and more polar lipids (phospholipids and free cholesterol) oriented near the surface. They also contain one or more specific proteins called apolipoproteins, that are located on their surface.

functions of the lipoproteins