Lipids Why this Chapter? Lipids are the largest and most diverse class of biomolecules To examine lipid structure, function, and metabolism

About Lipids Natural materials that preferentially extract into nonpolar organic solvents Includes fats, oils, waxes, some vitamins and hormones, some components of membrane General types: esters (“saponifiable”) and those that can’t be hydrolyzed

Waxes, Fats, and Oils Waxes - contain esters formed from long-chain (C16- C36) carboxylic acids and long-chain alcohols (C24-C36) Triacontyl hexadecanoate is in beeswax

Triacylglycerol Tri-esters of glycerol with three long- chain carboxylic acids, fatty acids.

Fatty Acids (from Fats and Oils) Straight-chain (C12 - C20) carboxylic acids Double bonds are cis-substituted but trans-fatty acids also occur A fat or oil in nature occurs as a mixture of many different triacylglycerols The most abundant saturated fatty acids are palmitic (C16) and stearic (C18)

Unsaturated and Polyunsaturated Fatty Acids Oleic (C18 with one C=C) and linolenic (C18 with 3 C=C) are the most abundant unsaturated

Soap A mixture of sodium or potassium salts of long-chain fatty acids produced by alkaline hydrolysis (saponification) of animal fat with alkali

Cleansing Action of Soap The carboxylate end of the long-chain molecule is ionic and therefore is preferentially dissolved in water The hydrocarbon tail is nonpolar and dissolves in grease and oil Soaps enable grease to be dissolved into water

Detergents “Hard” water contains Mg+2 and Ca+2 that form insoluble salts with soaps Synthetic detergents are alkylbenzene sulfonates that dissolve dirt like soaps but do not form scums with Mg+2 and Ca+2 .

Phospholipids Phospholipids are diesters of H3PO4, phosphoric acid Phosphoric acid can form monoesters, diesters and triesters In general these are known as “phosphates”

Phosphoglycerides Contain a glycerol backbone linked by ester bonds to two fatty acids and phosphoric acid Fatty acid residues with C12–C20 The phosphate group at C3 has an ester link to an amino alcohol

Sphingolipids The other major group of phospholipids Sphingosine or a dihydroxyamine backbone Constituents of plant and animal cell membranes Abundant in brain and nerve tissue, as coating around nerve fibers.

Phosphoglyceride Membranes Phosphoglycerides comprise the major lipid component of cell membranes Nonpolar tails aggregate in the center of a bilayer Ionic head is exposed to solvent

Steroids Steroids,are another class of nonsaponifiable lipid, defined by structure Has four fused rings A, B, C, and D, beginning at the lower left Carbon atoms are numbered beginning in the A ring The six-membered rings are in fixed chair conformations

Functions of Steroids In humans as hormones, steroids are chemical messengers secreted by glands and carried through the bloodstream to target tissues Also widely distributed as cholesterol

Adrenocortical Hormones Adrenocortical steroids: secreted by the adrenal glands near the upper end of each kidney Mineralocorticoids: control tissue swelling by regulating cellular salt balance Glucocorticoids: regulation of glucose metabolism and in the control of inflammation

Synthetic Steroids Made in pharmaceutical laboratories as new drugs Includes oral contraceptives and anabolic agents Methandrostenolone is an anabolic steroid used for tissue-building