Lipids - 4 Lipoprotiens 1Dr. Nikhat Siddiqi

Lipoproteins Group of molecular complexes found in the blood plasma of mammals. The plasma lipoproteins are spherical macromolecular complexes of lipids and specific proteins (apolipoproteins or apoproteins). 2Dr. Nikhat Siddiqi

The lipoprotein particles include chylomicrons, very-low-density lipoproteins (VLDL), low- density lipoproteins (LDL), and high-density lipoproteins (HDL). They differ in lipid and protein composition, size, density, and site of origin. 3Dr. Nikhat Siddiqi

Approximate size and density of serum lipoproteins Each family of lipoproteins exhibits a range of sizes and densities. 4Dr. Nikhat Siddiqi

Functions Lipoproteins function both to keep their component lipids soluble as they transport them in the plasma and to provide an efficient mechanism for transporting their lipid contents to (and from) the tissues. They contain several lipid soluble antioxidant molecules like  -tocopherol and carotenoids. 5Dr. Nikhat Siddiqi

Lipoprotein - Composition Lipoproteins are composed of a neutral lipid core (containing triacylglycerol, and cholesteryl esters) surrounded by a shell of amphipathic apolipoproteins, phospholipid, and nonesterified cholesterol. These amphipathic compounds are oriented so that their polar portions are exposed on the surface of the lipoprotein, thus making the particle soluble in aqueous solution. 6Dr. Nikhat Siddiqi

Size and density of lipoprotein particles Chylomicrons are the lipoprotein particles lowest in density and largest in size, and contain the highest percentage of lipid and the lowest percentage of protein. VLDLs and LDLs are successively denser, having higher ratios of protein to lipid. HDL particles are the densest. Plasma lipoproteins can be separated on the basis of their electrophoretic mobility, or on the basis of their density by ultracentrifugation. Dr. Nikhat Siddiqi7

Electrophoretic mobility of plasma lipoproteins. Dr. Nikhat Siddiqi8

Apopoteins The protein components of lipoprotiens are called apolipoproteins or apoproteins. They are synthesized in the liver. There are five major classes of apoproteins viz., A, B, C, D and E. 9Dr. Nikhat Siddiqi

Apolipoproteins: Functions The apolipoproteins associated with lipoprotein particles have a number of diverse functions, such as providing recognition sites for cell-surface receptors, and serving as activators or coenzymes for enzymes involved in lipoprotein metabolism. Some of the apolipoproteins are required as essential structural components of the particles and cannot be removed (in fact, the particles cannot be produced without them), whereas others are transfered freely between lipoproteins. 10Dr. Nikhat Siddiqi

Lipoproteins - Classification The lipoprotein particles include chylomicrons, very-low-density lipoproteins (VLDL), low- density lipoproteins (LDL), and high-density lipoproteins (HDL). They differ in lipid and protein composition, size, density and site of origin. 11Dr. Nikhat Siddiqi

Chylomicrons Chylomicrons are assembled in intestinal mucosal cells and carry dietary triacylglycerol, cholesterol, fat-soluble vitamins, and cholesteryl esters (plus additional lipids made in these cells) to the peripheral tissues. 12Dr. Nikhat Siddiqi

Very Low Density Lipoproteins VLDLs are produced in the liver. They are composed predominantly of triacylglycerol (approximately 60%), and their function is to carry this lipid from the liver to the peripheral tissues. 13Dr. Nikhat Siddiqi

Low Density Lipoproteins LDL are the principle transporters of cholesterol and cholesteryl esters to the tissues. 14Dr. Nikhat Siddiqi

High Density Lipoproteins Rich in protein Synthesized in the liver and intestine. Scavenge excessive cholesterol from cell membrane and cholesteryl esters from VLDL and LDL. 15Dr. Nikhat Siddiqi

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