BIOCHEMISTRY_SELF DIAGNOSTIC EXAM.pdf

Chemistry of Lipids ISIDORE A. BILIRAN, M.D., R.M.T. Assistant Professor I Cebu Doctors’ University – College of Medicine Department of Biochemistry Genetics Systems Coordinator (Level 1 & 2) Member – Philippine Association of Academic Biochemists...

Chemistry of Lipids ISIDORE A. BILIRAN, M.D., R.M.T. Assistant Professor I Cebu Doctors’ University – College of Medicine Department of Biochemistry Genetics Systems Coordinator (Level 1 & 2) Member – Philippine Association of Academic Biochemists  Include: Lipids Fats Oils Waxes Lipids Heterogenous group of compounds related to fatty acids Properties Relatively insoluble in water Soluble in non-polar solvents Ether Chloroform Benzene Carbon tetrachloride Functions of Lipids Important dietary constituents High energy value Fat soluble vitamins Thermal insulator Subcutaneous tissues Functions of Lipids Non-polar lipids Act as electrical insulators Allow rapid propagation of depolarization waves along myelinated nerves Lipoproteins Combination of fats & proteins Important cellular constituents Serves as means of transporting lipids in the blood  Classification of Lipids Simple Lipids Neutral fats Waxes True waxes Cholesterol esters Vitamin esters (Vit.A, Vit.E) Compound Lipids Phospholipids Glycolipids / cerebrosides Sulfolipids Lipoproteins Lipopolysaccharides  Classification of Lipids Derived Lipids Fatty acids Monoglycerides / diglycerides Alcohols Miscellaneous Lipids Simple Lipids Esters of fatty acids with various alcohols Neutral fats Triesters of fatty acids & glycerols Triacylglycerols Triglycerides Fats in the liquid state is called oil  Waxes Esters of fatty acids with higher MW monohydric aliphatic alcohols True waxes Cholesterol esters Vitamin esters  True waxes Product of both animal & vegetable origin Fatty acid components of esters Palmitic Stearic Oleic Cholesterol esters Esters of fatty acids with cholesterol Compound Lipids Esters of fatty acids containing groups in addition to alcohol & fatty acids Phospholipids Lipids containing (in addition to fatty acids & alcohol): Phosphoric acid residue Nitrogenous base  Glycolipids a.k.a. Cerebrosides Lipids containing: Carbohydrates Nitrogenous bases Does NOT contain: Phosphate glycerol  Sulfolipids Posess sulfate groups Lipoproteins Lipids attached to proteins Lipopolysaccharides Lipids attached to polysaccharides Derived Lipids Derivatives obtained by hydrolysis of simple/compound lipids Still possess the general physical characteristics of lipid Includes: Saturated/unsaturated fatty acids Monoglycerides/diglycerides  Alcohols Straight-chain alcohols Water-soluble High MW Obtained on hydrolysis of waxes Sterols/steroids Vitamin D Alcohols containing beta-iodine ring Vitamin A Carotenoids Miscellaneous Lipids Aliphatic hydrocarbons Isooctadecane (liver fat) Beeswax/plant waxes Carotenoids Squalene Terpenes Vitamin E Vitamin K Triacylglycerols Fats & Oils Triesters of glycerol & various fatty acids Vegetable Oils Triacylglycerols that are liquid at room temperature Highly unsaturated Shorter length Triacylglycerols The most abundant, naturally-occuring lipids Fat represents a complex mixture of triglycerides Nomenclature of Triacylglycerols Glycerols of: Simple Mixed Triacylglycerols Triacylglycerols Palmitic acid Tripalmitin Dipalmito-olein Oleic acid Triolein Palmito-diolein Dipalmito-olein Stearic acid Tristearin Stearo-dipalmitin Palmito-oleo-stearin Oleo-palmito-stearin Dipalmito-stearin Tripalmitin Triolein Tristearin Oleo-palmito-stearin Hydrolysis of Triacylglycerols Triacylglycerol can be hydrolyzed by: Alkalis Fat-splitting enzymes (lipase) Acids Superheated steams Tripalmitin + sodium hydroxide (alkali) Glycerol + sodium palmitate (soap)  Soaps Metallic salts of fatty acids Serve as detergents Because of their ability to form micelles Classified as: Soft soap Hard soap  Soft soap Aka soluble soap Have cleansing properties Sodium soap Potassium soap (liquid) Hard soap Aka insoluble soap Magnesium soap Calcium soap It is useless to use cleansing soaps when bathing in sea water The heavy metallic components of seawater will convert the soft soaps to hard soaps  Micelles Hydrocarbon chains are arranged in a way that: Carboxylate groups are at the surface (forming a hydrophobic core) Hydrophilic groups are at a lipid-water interface Stabilized by the association of anionic groups with the water molecules Dirt, fat & other substances are dissolved in the hydrophobic core & washed away by water PHOSPHOLIPIDS Composed of: Fatty acids Glycerol Phosphoric acid Nitrogenous base Fatty acyl derivatives of: L-glycerol-3-phosphate D-glycerol-3-phosphate Phosphatidic Acid The starting compound in the formation of a series of derivatives with nitrogenous bases such as: Choline Ethanolamine Serine Inositol (hexahydroxylcycloxane) Examples of Phospholipids Phosphatidyl choline / Lecithin Phosphatidyl ethanolamine / Cephalin Phosphatidyl serine Phosphatidyl inositol Cardiolipins Sphingomyelins Phosphatidyl choline / Lecithin Contains: Glycerol 2 fatty acids (alpha & beta position) Phosphoric acid Choline  Normal Surface Tension Decreased Surface Tension Lecithin (Surfactant) decreases surface tension  Enzymes that Act on Lecithin Enzyme Breakdown products Phospholipase-A1 Simultaneously attack the ester 2 fatty acids bond in the alpha & beta glycerophosphorylcholine positions Phospholipase-A2 Found in: Fatty acid Cobra venom Lysolecithin Black widow spider venom (potent hemolyzing agent Hydrolyzes the ester bond in the Hemolyzes RBCs causing beta-position death) Phospholipase-C Attacks the ester bond of C-3 Diglyceride phosphorylcholine Phospholipase-D Attacks the phosphorylcholine Phosphatidic acid bond choline Phosphatidyl ethanolamine Blood coagulant On hydrolysis will liberate: Glycerol Phosphoric acid 2 fatty acids Nitrogenous base (ethanolamine) Phosphatidyl serine Will produce on hydrolysis: 2 fatty acids Glycerol Phosphoric acid (serine) Phosphatidyl inositol On hydrolysis will produce: 2 fatty acids Glycerol Phosphoric acid Hexahydroxycyclohexane (inositol) Cardiolipins [Phosphatidyl Glycerol] Important phospholipids found in the mitochondrial membrane Rich in polyunsaturated fatty acids (linoleic acid) Contains: 2 glycerol 2 phosphoric acid 4 fatty acid residues (mostly unsaturated) Does NOT contain: Nitrogenous base Any other radicals Sphingomyelins Phospholipids found frequently in membranes Do NOT have any glycerol Contains: Sphingosine An unsaturated aliphatic amino alcohol Serves as the backbone Amine Makes up a chemical compound (ceramide) together with sphingosine Phosphoric acid Makes up the hydrophilic end  Amphipathic Contains both hydrophobic & hydrophilic ends Hydrophobic (Spingosine) Hydrophilic (Phosphoric acid) GLYCOLIPIDS [Cerebrosides] On hydrolysis will yield: Sphingosine / dihydrosphingosine Fatty acid Sugar (galactose/glucose) Contain nitrogen but no phosphorus Insoluble in ether  Soluble in: Acetone Hot alcohol Benzene chloroform Occur in: Extramedullary sheaths of nerves Brain tissues (white matter) Constituent of the external surface of the cellular plasma membrane  Sphingosine Provides the backbone for the glycolipid structure Ceramide Formed when fatty acid is bound by an amide bond to the amino group of sphingosine  Cerebroside Formed when the ceramide moiety is linked to a monosaccharide [glucose(glucocerebroside) or galactose(galactocerebroside)] united by a glycosidic bond found in the myelin sheath of the brain & peripheral nerves Differentiated by the type of fatty acids present in their molecule  Cerebroside Kerasin Contains lignocerate (cerebron) with hydroxylignocerate (cerebronate) Nervon Contains unsaturated homologue of lignocerate (nervonate) Oxynervon Has the hydroxy derivative of nervonate as its constituent fatty acid  Gaucher’s Disease Congenital & familial disease Kerasin & other lipids are deposited in large quantities in the spleen & liver (causing enalrgement of these organs) Glucocerebrosidase  Sulfatides In which the galactose residue is sulfated Gangliosides Complex glycolipids that occur in the brain Contain: Sialic acid Ceramide 3 molecules of hexose (glucose/galactose) STEROLS Monohydroxy alcohols Belong to the steroid compound cyclopentaperhydrophenantrenes Have a 4-ring structure Differ from each other in the: Arrangement of double bonds in the rings Presence of oxygen/hydroxyl/other groups Presence of breaks in one of the rings Cholesterol The most important sterol Widely distributed Known as the mother substance of other steroids A constituent of all animal cells Present in high concentrations in: Corpus luteum Adrenal cortex Can be seen in the blood & bile Major component of gallstones Cholesterol Soluble in many fat solvents Can be easily crystallized from fat solvents Ether Chloroform Benzene Hot alcohol Can take up 2 halogens Since it has an unsaturated bond Unsaponifiable Cholesterol Gives a number of color reactions Forms the basis for its quantitative determination Salkowski’s test (qualitative) Lieberman-Burchard’s test (quantitative)  Sex hormones Estrogen Progesterone Testosterone PROGESTERONE Adrenocortical hormones Collectively known as cortisone Separated into various components Mineralocorticoids Glucocorticoids Bile Acids Secreted in the bile in the form of their sodium salts Taurocholic acid Glycocholic acid Taurocholic acid  Cardiac glycones Cardiac glycosides used in the treatment of cardiac anomalies Ergosterol Found in the skin Converted to vitamin D2(ergocalciferol) upon exposure to UV radiation (sunlight) PROPERTIES of LIPIDS PHYSICAL PROPERTIES Fats Oil solid at room temperature liquid at room temperature high MW saturated fatty acids Low MW Saturated / unsaturated High congealing point Low congealing point High melting point Low melting point Non-volatile (long-chained / Volatile (short-chained / saturated) unsaturated) Fats Float on water Sp.Gr.: