1LipidsSung Woo KimNorth Carolina State UniversityWhat we will learn: Characteristics Classification Fatty acids Triglycerides Fat and oils in animal feeds Digestion Absorption MetabolismCharacteristics Organic compounds mainly containingC, H, O (and sometimes P, N) Relatively insoluble in water Relatively soluble in organic solvents Serve important biochemical and physiological functions in plant and animal tissues2Classification1. Simple lipids 2. Compound lipids(oil, fat, waxes)(phospholipid, glycolipid, LP)3. Derived lipids4. Sterols5. Terpene(fatty acid, glycerol)(cholesterol, estrogen)(retinoid, terpenoid)1. Simple lipids Esters of fatty acids with various alcohols Fat & oils: esters of fatty acids with glycerol Waxes: esters of fatty acids with alcohols other than glycerol (alkanes, ketones, etc.)DGglycerolFatty AcidTGMGTri- / Di- / Mono-acylglyceride2. Compound lipids Esters of fatty acids containing non-lipid substances such as phosphorus, carbohydrates and proteins in additioncarbohydrates, and proteins in addition to an alcohol Phospholipid (phosphatides): fats containing phosphoric acid (and N) Glycolipid: fats containing carbohydrates (and often N) Lipoproteins: lipids bound to proteins33. Derived lipids Substances derived from simple or compound lipids by hydrolysis  Fatty acids Glycerol Other alcohols4. Sterols Structure One of the characteristics is the “steroid l”fffd3nucleus” consisting of four fused rings: 3 rings with 6 carbons and 1 ring with 5 carbons.  Examples are cholesterol, ergosterol, bile acids, androgens, estrogens, progesterones4. Sterols45. Terpenes Compounds that usually have isoprene-type structures (retinoid, terpenoid, and f‘h b l il ti l il ’)many of ‘herbal oils =essential oils’)IsopreneMono-terpenes Sesqui-terpenes Tri-terpenes2 isoprene units 3 isoprene units6 isoprene unitsFunctions1. Energy supply: energy dense2. Source of essential fatty acids: linoleic acid, CHO: 4.10 kcal/gProtein: 5.65 kcal/gLipid: 9.45 kcal/gEthyl alcohol: 7.11 kcal/glinolenic acid3. Carrier of fat-soluble vitamins: A, D, E, K4. Integral constituent of cell membranes5. Carrier of steroid hormones FATTY ACID5Structure Consist of 2 to 30 carbon atoms (12-24 is most common) including carbon from a carboxyl groupHydrocarbon chainCarboxylgroupcarboxyl group. Carboxyl group (COOH) is attached to the end of each carbon chain.  The carbon chain is typically linear. Fatty acid usually contains an even number of carbons.Why would a ‘typical fatty acid’ have an even number of carbons? Fatty acid biosynthesis Substrates are acetyl-CoA Acetyl-CoA: contains 2 carbons So, biosynthesis of a fatty acid is a process of accumulating 2-carbon units from acetyl-CoA.3C Pyruvate3C PyruvateCytoplasm Mitochondria6C Glucose2C Acetyl-CoAFatty acid2C Acetyl-CoATCA CycleCitrate Citratex n6Structure R-COOH (basic structure)where R is a carbon chain of variable length:CH(CH)hydrocarbon chainCarboxylgrouplength: CH3(CH2)nExamples:CH3COOH (acetic acid)CH3(CH2)2COOH (butyric acid)CH3(CH2)14COOH (palmitic acid)Structure (C numbering)ω-1ω-2ω-3Δ1Δ2C18:0 (Stearic acid)Amphipathic propertyHydrophilic carboxyl groupHydrophobic hydrocarbon chain7Surface membraneAmphipathic propertydhlhdHydrophobic tailMicelleWaterHydrophilic headMicelle: a lipid structure in aqueous environmentAmphipathic property Fatty acids vary depending on  Length of hydrocarbon chainDegree of saturation Degree of saturation Over 1,000 types but 20 are commonly found Saturated vs. unsaturated When carbon chain is not saturated with hydrogen (=unsaturated), carbon to carbon double bond (C=C) are found in naturally occurring fatty acids8Degree of saturation (plant)=Δ9,10 carbon=Δ1ω-1ω-2ω-3=by desaturase==Δ1Δ12,13 carbonΔ2saturated fatty acid(stearic acid)(C18:0)UN(oleic(linoleic(C18:1)(C18:2)Δ15-16 carbon(linolenic(C18:3)=Degree of saturation Fatty acid desaturase  Removes two H atoms from a fatty acid, creating a C-C double bondPl t d t t t∆910∆1213d∆1516Plant: desaturate at ∆9-10, ∆12-13, and ∆15-16(simple steps) Animal: desaturate at ∆9-10, ∆6-7, ∆5-6, and ∆4-5, but with elongation by an enzyme: ‘elongase’ (complicated multiple steps)=AnimalPlant Unsaturated fatty acids can have One or up to six double bonds naturallyDegree of saturationcisconfiguration naturally (by desaturase)==Cis configuration Trans configuration9 Unsaturated fatty acids can have One or up to six double bonds naturallyDegree of saturationcisconfiguration naturallyTransconfiguration can be produced by microorganism (dairy milk product), or partially during artificial hydrogenation of vegetable oils to produce margarineTransDegree of saturationΔ9 carbonTransCis……StraightBendedDegree of saturationSaturated FA Cis-Unsaturated FASolid (packed)Liquid (bulky)10Degree of saturationSaturated FA Trans- Cis-Unsaturated FASolid (packed)Liquid (bulky) C18:0 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 11 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18HHHHHHHHHHHHHHHHH|||||||||||||||||H-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-COOH|||||||||||||||||HHHHHHHHHHHHHHHHH Name: # carbon: # double bonds:stearic acid180 C18:1 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1HHHHHHHHHHHHHHHHH|||||||||||||||||H-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-COOH|||||||||||||||||HHHHHHHHHHHHHHHHH-1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18→ C18:1 9c Name: # carbon: # double bonds:cisor trans?: Enzyme:oleic acid181cis-configuration∆9-desaturase11 C18:2 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1HHHHHHHHHHHHHHHHH|||||||||||||||||H-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-COOH|||||||||||||||||HHHHHHHHHHHHHHHHH--1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18→ C18:2 9c 12c Name: # carbon: # double bonds:cisor trans?: Enzyme:linoleic acid182cis-configuration∆9- / ∆12-desaturases ω-3 or ω-6? C18:3 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1HHHHHHHHHHHHHHHHH|||||||||||||||||H-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-COOH|||||||||||||||||HHHHHHHHHHHHHHHHH---1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18→