Lipids

Biological compound soluble in non-polar solvent Chemically heterogeneous: Simple or Complex Simple Lipid: alcohol + one or more fatty acids Complex lipid: alcohol + fatty acid + something else

Lipid molecule

Classification of Lipids

Fatty Acids Linear Molecules carbons in length Even number of carbons No other functional groups but carboxyl Sometimes alkene groups C=C – Saturated vs. unsaturated

Water Solubility Hydrophobic part of molecule dominates: very insoluble in water Forms micelles in water

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Fatty Acid Nomenclature Nomenclature reflects location of double bonds also used are common names (e.g., oleic, stearic, palmitic) linoleic is also known as 18:2 n-6 this means the FA is 18 carbons in length, has 2 double bonds, the first of which is on the 6th carbon arachidonic = 20:4 n-6 this means the FA is 18 carbons in length, has 4 double bonds, the first of which is on the 6th carbon

Saturated vs. Unsaturated Fatty Acids saturated: the SFA’s of a lipid have no double bonds between carbons in chain polyunsaturated: more than one double bond in the chain most common polyunsaturated fats contain the polyunsaturated fatty acids (PUFAs) oleic, linoleic and linolenic acid unsaturated fats have lower melting points stearic (SFA) melts at 70 o C, oleic (PUFA) at 26 o C

saturated Fatty Acids Fatty Acid # of Carbons # of C=C lauric120 myristic140 palmitic160 stearic180

Unsaturated Fatty Acids Fatty Acid # of Carbons # of C=C oleic181 linoleic182 linolenic183 arachadonic204

14 Properties of Fats and Oils Triacylglycerols in natural fats and oils are nonpolar, hydrophobic molecules with no ionic charges. Oil: A mixture of triacylglycerols that is liquid because it contains a high proportion of unsaturated fatty acids. Fat: A mixture of triacylglycerols that is solid because it contains a high proportion of saturated fatty acids.

15 The hydrocarbon chains in saturated acids are flexible and uniform in shape, allowing them to nestle together. By contrast, the carbon chains in unsaturated acids have rigid kinks wherever they contain cis double bonds. The kinks make it difficult for such chains to fit next to each other in the orderly fashion necessary to form a solid.

Melting Points Increases with size (lesser effect) Decreases with unsaturation (greater effect)

Cis vs Trans Fatty Acids Cis fatty acids occur naturally Trans fatty acids occur during hydrogenation reactions

Triglycerides: Fats and Oils Glycerol + 3 Fatty Acids Connected by ester bonds

Triglyceride

Fat or Oil Depends on melting point- solid or liquid at room temperature Depends mostly on degree of unsaturation Animal Fats more saturated, plant oils more unsaturated

Waxes Long chain fatty acid + long chain fatty alcohol Myristyl palmitate

Wax Block Diagram

Phosphoglycerides Glycerol, 2 fatty acids, phosphate + another alcohol Glycerol Fatty Acid Phosphate alcohol

Phosphatidic acid

Alcohols used in phosphoglycerides serine ethanolamine choline

Phosphatidyl Choline (lecithin) Lectithin used as emulsifier Dipalmitoyl phosphatidyl choline formed as surfactant in lung cells

Phosphatidyl serine: a cephalin found in cell memranes

Sphinglipids: Sphingosine + fatty acid + something else Sphingosine

Ceramide: sphingosine + fatty acid Sphingosine

Sphingomyelin: sphingosine, fatty acid, phosphate and choline Sphingomyelins found in myelin sheath around neurons

Sphingomyelin Fatty acid phosphate choline

Glycolipid: Lipid + Carbohydrate Cerebroside: Sphingosine + fatty acid + carbohydrate

Lipid Storage Diseases

Steroids Non-saponifiable lipids derived from cholesterol Steroid Ring System

Cholesterol Found in Diet (animal fats) Endogenous synthesized in liver

Cholesterol Essential component of cell membranes Used as raw material for sex hormones and adrenocorticoid hormones Used to make bile salts High blood levels also associated with heart disease, atherosclerosis, arterial plaques

Cholesterol transported as Lipoprotein complex (LDL)

lipoproteins Low Density Lipoproteins (LDL) – is made by the liver and is comprised of cholesterol that is delivered to the cells in the body – High levels of LDL is strongly correlated with heart disease High Density Lipoproteins (HDL) - made by the liver and picks up cholesterol from the cells fro recycling or excretion – High levels of HDL is inversely correlated with heart disease – It is protective

Lipoproteins classified by Density HDL: High-density Lipoprotein LDL: Low-density Lipoprotein VLDV: Very low-density Lipoprotein – Triglycerides and cholesterol Chylomicron – Mostly triglycerides

Biological flow of Cholesterol

Bile Salts: Glycocholate Act as emulsifying agents to digest fats Method for excreting cholesterol- bile is emulsion of cholesterol and bile salts Gall stones form when cholesterol gets too concentrated

Adrenocorticoid hormones Glucocorticoids: – regulate blood glucose levels – Cortisol and Cortisone – Also regulate inflammation, used to treat inflammatory diseases Mineralcorticoids: – influences blood Na + and Cl - levels – Aldosterone most important

cortisol cortisone aldosterone

Male Sex Hormones Testosterone – Produced by testes – Male genitals and secondary sex characteristics – Muscle growth Anabolic Steroids (fake testosterone) – Intended to prevent muscle atrophy – Used by athletes, widely banned – Bad side effects

Female Sex Hormones Estrogen(estradiol, estrone) and progersterone – Produced by ovaries – Reproductive cycle and secondary female characteristics Mimicked by birth control pills

Prostaglandins Hormone like action – Regulates fever, contractions, inflammation – Induces labor, and asthma – Made from arachadonic acid – Synthesis inhibited by aspirin and cyclooxygenase inhibitors

Functions of lipids Excellent energy reserves Structure of cell membranes Organ padding Body thermal insulation Essential fatty acids (EFA) Hormone synthesis Fat soluble vitamin absorption

Biological Membranes Separates cell interior from exterior, or cellular organelles from cytoplasml About 60% lipid and 40% protein – Lipid mostly phosphoglyceride, sphingomyelin and cholesterol Found as Lipid Bilayer

Lipid Bilayer