Lipid 1 for 2nd Students PDF

FD%2520KODAS%25205 CHEMISTRY OF LIPIDS Dr :Marwa El-Beltagy  Organic substances relatively insoluble in water but soluble in organic solvents like chloroform, ether and benzene Lipids vary widely in their structures. They have mostly C,H and some have a few polar atoms/ functional groups....

FD%2520KODAS%25205 CHEMISTRY OF LIPIDS Dr :Marwa El-Beltagy  Organic substances relatively insoluble in water but soluble in organic solvents like chloroform, ether and benzene Lipids vary widely in their structures. They have mostly C,H and some have a few polar atoms/ functional groups. Related more by their physical than by their chemical properties.  Important in understanding many areas of interest obesity and atherosclerosis. Cardiovascular diseases Diabetes Fatty liver Simple Complex Derived lipid lipid lipids  Wax Neutral fat e.g. Cholesterol Ester Triglyceride (TG) = Triacylglycerol (TAG) Solid at room Solid (Fat) Or Liquid (Oil) temperature Glycerol Long chain 3 Fatty acids Fatty acid Alcohol Alcohol ❑ Fats and oils are ❑ also called triglycerides. ❑ esters of glycerol+ 3 FA Fatty Acids Triglyceride FORMS OF TAG Body TAG Source of dietary TAG energy Animal fixation plants Heat insulator marine When hydrolysis of waxes gives : one fatty acid + alcohol EXAMPLES ✓ Beeswax  CH2 OH 2 H2O CHO HO CH CH Heating, KHSO4 CH2 OH CH2 Glycerol Acrolein ACROLIEN :aldehyde has characteristic odor 6/29/2012 Biochemistry for medics 16 ❑ Fatty acids are ❑ Aliphatic monocarboxylic organic acids with hydrocarbon side chain. ❑ insoluble in water. ❑ General formula R-COOH. ❑ R ----Alkyl / hydrocarbon chain ❑ COOH----- Carboxyl end ❑ Occurs mainly as ESTERS in natural fats and oils. Fatty acids that occur in natural lipids are of even carbons (usually 14C – 20C) This is due to biosynthesis of fatty acids mainly occurs with the sequential addition of 2 carbon units. Palmitic acid (16C) and Stearic acid (18C) are most common. Propionic acid (3C) and valeric acid (5C) are common odd chain fatty acids. -Fatty acids are amphipathic molecules composed of a hydrophilic (polar, ionized) head (formed by the carboxyl group) and a hydrophobic (non- polar, non-ionized) tail ( formed by the hydrocarbon chain). The degree of solubility of a fatty acid depends on the length of the hydrocarbon chain. Classification of fatty acids According to chain length short, medium and long 2. According to degree of saturation saturated & unsaturated 3. According to Biological value essential & non-essential 4. Aliphatic, branched and cyclic Fatty acids are saturated with all single C–C bonds. are solids at room temperature unsaturated with one or more double C=C bonds. are liquids at room temperature. Contains one double Contains bond more than one double bond  Saturated Fatty Acids Number of C Common Name Systemic Name Formula atoms 2 Acetic acid Ethanoic acid CH3COOH 4 Butyric acid Butanoic acid CH3(CH2)2COOH 6 Caproic acid Hexanoic acid CH3(CH2)4COOH 8 Caprylic acid Octanoic acid CH3(CH2)6COOH 10 Capric acid Decanoic acid CH3(CH2)8COOH 12 Lauric acid Dodecanoic acid CH3(CH2)10COOH 14 Myristic acid Tetradecanoic acid CH3(CH2)12COOH 16 Palmitic acid Hexadecanoic acid CH3(CH2)14COOH 18 Stearic acid Octadecanoic acid CH3(CH2)16COOH 20 Arachidic acid Eicosanoic acid CH3(CH2)18COOH 6/29/2012 22 Behenic acid Docosanoic acid Biochemistry for medics CH3(CH2)20COOH 25 Unsaturated fatty Acids Unsaturated fatty acids may further be divided as follows- (1) Monounsaturated (monoethenoid, monoenoic) acids, containing one double bond. (2) Polyunsaturated (polyethenoid, polyenoic) acids, containing two or more double bonds. The configuration of the double bonds in most unsaturated fatty acids is cis. The double bonds in polyunsaturated fatty acids are separated by at least one methylene group. 6/29/2012 Biochemistry for medics 26  Unsaturated Fatty Acids S.No. Number of C Family Common Name Systemic Name atoms, number and location of double bonds [A] Monoenoic acids (one double bond) 1. 16:1;9 ω7 Palmitoleic acid cis-9-Hexadecenoic 2. 18:1;9 ω9 Oleic Acid cis-9-Octadecenoic 3. 18:1;9 ω9 Elaidic acid trans 9- Octadecanoic [B] Dienoic acids (two double bonds) 1. 18:2;9,12 ω6 Linoleic acid all-cis-9,12- 6/29/2012 Biochemistry for medics Octadecadienoic 27 S.No. Number of C atoms, Family Common Name Systemic Name number and location of double bonds [c] Trienoic acids (three double bonds) 2. 18:3;9,12,15 ω3 α-Linolenic all-cis- 9,12,15Octadecatrieno ic [D] Tetraenoic acid(Four double bonds) 20:4;5,8,11, ω6 Arachidonic all-cis-5,8,11,14- 14 Eicosatetraenoic 6/29/2012 Biochemistry for medics 28  Saturated Unsaturated No double bonds contain double bond(s) Polyunsaturated Short-chain Long- chain Monounsaturated More than one 2-10 carbons More than 10 C One double bond double bond Essential fatty Acetic acid acids Palmitic Oleic Propionic Palmitoleic Stearic Butyric Linolenic liquid Solid Linoleic Liquid Arachidonic water soluble liquid 6/29/2012 Biochemistry for medics 31 6/29/2012 Biochemistry for medics 33  Hydrogenation Unsaturated compounds react with H2 Ni or Pt catalyst & heat are used to make margarine and other hydrogenated items. Saponification and Soap Hydrolysis with a strong base NaOH and KOH Triglycerides split into glycerol and the salts of fatty acids The salts of fatty acids are “soaps” KOH gives softer soaps Emulsification????? Cis and Trans forms of fatty acids 6/29/2012 Biochemistry for medics 39 Branched fatty acids (Refsum s̓ disease) Phytanic acid 3,7,11,15-tetramethyl hexadecanoic acid) is a branched chain fatty acid that humans can obtain through the consumption of dairy products, ruminant animal fats, and certain fish. Refsum disease, an autosomal recessive neurological disorder , have impaired α-oxidation activity and accumulate large stores of phytanic acid in their blood and tissues.(brain) Rancidity It is toxic reaction of TAG due to oxidation or hydrolysis of fats and oils when exposed to air, light, moisture or by bacterial action, resulting in unpleasant taste and odor. Oxidative Hydrolytic ketonic  Lipid peroxidation