LIPIDS III

STEROLS Cholesterol Male & female sex hormones Bile acids Vitamin D Adrenal corticosteroids

Sterols Compounds with multi-ring structure Insoluble in water Present both in plant and animal foods Major sterol is cholesterol However, cholesterol is found only in animal products (manufactured in liver) High content in organ meats and egg yolk

Structure of steroid hormones:

Common Sterol Compounds Vitamin D3 (cholecalciferol)

Bile acids (bile salts) are polar derivatives of cholesterol, formed in liver and secreted into the gall bladder. They pass via the bile duct into the intestine, where they aid digestion of fats & fat-soluble vitamins. Bile acids are amphipathic, with detergent properties. Bile acids emulsify fat globules into smaller micelles, increasing the surface area accessible to lipid-hydrolyzing enzymes. They also help to solubilize lipid breakdown products (e.g., mono- & diacylglycerols from triacylglycerol hydrolysis).

Lipoproteins Molecular complexes found in blood plasma Contain: Neutral lipid core of cholesterol esters and/or TAGs Surrounded by a layer of: Phospholopid Cholesterol Protein Classes: Chylomicrons, VLDL, LDL, HDL

Model Structure of a Plasma Lipoprotein

Major Classes of Lipoproteins Chylomicrons: Very large and very low density Transport intestineadipose VLDL: Made in liver Transport lipids to tissues LDL: carry cholesterol to tissues HDL: Scavenge excess cholesterol esters “Good cholesterol”

C P T 100% T P C C P T C P T 80% 60% Composition 40% 20% 0% Chylo- microns VLDL LDL HDL Lipoprotein Type The major classes of lipoproteins and their relative content of triacylglycerol (T),cholesterol (C) and protein (P).

Relative Composition of Lipoproteins

Lipid peroxidation a non-enzymatic reaction catalyzed by oxygen may occur in tissues or in foods (spoilage) the hydroperoxide formed is very reactive and leads to the formation of free radicals which oxidize protein and/or DNA (causes aging and cancer) principle is also used in drying oils (linseed, tung, walnut) to form hard films

Learning Check PL1 Identify each lipid as: (1) phospholipid (2) steroid (3) triglyceride (4) sphingolipid A. Cholesterol Glycerol, 2 fatty acids, phosphate, and choline Glyceryl tristearate Sphingosine, fatty acid, phosphate, and choline Estradiol Bile salts Most of plasma membranes

Solution PL1 A. 2 steroid B. phospholipid C. 3 triglyceride D. 4 sphingolipid E. 2 steroid F. 2 steroid G. 1 phospholipid

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