Lipids

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

Classification of Lipids

Fatty Acids Linear Molecules 10-20 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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saturated Fatty Acids Fatty Acid # of Carbons # of C=C lauric 12 myristic 14 palmitic 16 stearic 18

Unsaturated Fatty Acids # of Carbons # of C=C oleic 18 1 linoleic 2 linolenic 3 arachadonic 20 4

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.

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

Alternate View of Fatty Acids

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

Dietary Fatty Acids Saturated fats associated with Heart Disease Promotes higher levels of blood cholesterol Animal fats also contain cholesterol, plants have no cholesterol

Chemical Properties of Triglycerides 1. Reaction with I2 Used to quantitate unsaturation in fats Product is colorless, I2 is colored Iodine number = grams I2 reacting with 100 g fat

2. Hydrolysis of Ester: catalyzed by acid or enzyme

3. Saponification with NaOH

Saponification Reaction produces Soaps Hydrophilic and hydrophobic regions Hydrophobic dissolved in oils Hydrophilic stays on the surface Insoluble salts form with hard water Sodium stearate Sodium dodecyl sulfate

4. Hydrogenation Reacts with alkene Partial or complete hydrogenation Produces more saturated fat Changes plant oil to margarine

Review of Chemical Reactions

Artificial Fats Simpless: micro-particles of proteins Smooth cream texture Not heat stable 1.3 Cal/gram vs. 9 Cal/gram for fats Olestra: polymer of sucrose and fatty acids Not digestable Taste and texture of fats Causes loss of fat soluble vitamins and other side effects

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

Wax Block Diagram

Phosphoglycerides Glycerol, 2 fatty acids, phosphate + another alcohol

Phosphatidic acid

Alcohols used in phosphoglycerides choline serine ethanolamine

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

Ceramide: sphingosine + fatty acid

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

Sphingomyelin Fatty acid choline phosphate

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

Lipid Storage Diseases

About 60% lipid and 40% protein 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

Blood Type Antigens Glc = glucose Gal = galactose GalNAc = N-acetylgalactosamine Fuc = fucose

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 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

Anabolic Steroids (fake testosterone) 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

Estrogen(estradiol, estrone) and progersterone 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

Classification of Lipids