Lipids Note 1 PDF

LIPIDS LIPIDS CHEMISTRY  Outline  Overview of Lipids  Classification  Functions & Clinical Significance  Chemistry and properties  Fatty Acids, TGs, PLPs, Waxes, & PGs  Lipid micelles, monolayers & bilayers  Sterols  Lipoprotein system  LIPIDS  Lipids...

LIPIDS LIPIDS CHEMISTRY  Outline  Overview of Lipids  Classification  Functions & Clinical Significance  Chemistry and properties  Fatty Acids, TGs, PLPs, Waxes, & PGs  Lipid micelles, monolayers & bilayers  Sterols  Lipoprotein system  LIPIDS  Lipids are heterogeneous organic substances that are relatively insoluble in water (hydrophobic) but soluble in organic solvents (benzene, chloroform, ethanol, ether, CCL4, acetone, etc)  Lipids consist of alcohol and fatty acids joined together by ester linkage  Functions of lipids 1. Reservoir of energy e.g. Triglycerides - 9 Kcal/g; supplies 60% of body’s energy need 2. Important constituents of cell membrane e.g. phospholipids, cholesterol 3. As insulators on the neurons e.g. myelin sheath 4. Protect internal organs by cushioning effect 5. Provide shape and contour to the body 6. Act as surfactants, detergents and emulsifying agents e.g. lecithin, sphingomyelin, bile acid, e.t.c. 7. Helps in the regulation of metabolic processes. e.g. steroid hormones, prostaglandins 8. Contributes flavor, aroma and palatability of foods 9. Protects against changes due to external heat e.g. 10. subcutaneous fat 10.Helps in the absorption of fat soluble vitamins  Clinical significance of lipids To know the diseases associated with abnormal metabolism of lipids such as:  Obesity  Atherosclerosis  Hyperlipidemia/Hypercholesterolemia  Diabetes mellitus  Fatty liver  Lipid storage diseases e.g. Gauchers, Niemann- Pick, Fabry’s & Tay-Sach’s diseases  CLASSIFICATION OF LIPIDS TGs & Phospholipids, steroids, cholesterol, waxes glycolipids (cerebroside, PGs, globoside, ganglioside), leukotrienes sulpholipids & lipoproteins I. Simple lipids a. Triacylglycerol/triglycerides/neutral fats b. Waxes: esters of FA with alcohol II. Compound 1. lipids Phospholipids a. Nitrogen containing phospholipids: lecithin, cephaline, phosphatidyl serine b. Non-nitrogen containing phospholipids: phosphatidyl inositol, phosphatidyl glycerol, cardiolipin (diphosphatidyl glycerol)  c. Plasmalogens: lipids with long chain alcohol. e.g. choline & ethanolamine. d. Phosphosphingosides: e.g. sphingomyelin 2. Non-phosphorylated lipids. Examples a. Glycolipids: e.g. cerebrosides, globosides, gangliosides b. Sulpholipids: e.g. Sulphated glycolipids III. Examples: steroids including cholesterol, prostaglandins, leukotrienes, terpenes, etc IV. Lipids conjugated with other compounds: e.g. lipoproteins, glycolipids, etc  EXAMPLES OF LIPIDS 1. Triglycerides 2. Phospholipids 3. Steroids (cholesterol & others) TRIGLYCERIDE S  TRIGLYCERIDES Esters of FAs with alcohol Predominant form of fat in foods and major fuel store in the body Sources – exogenous ie. Dietary (90% of 60 -150g adult lipid intake per day), and endogenous (mainly by liver & adipose tissue) Structure – composed of 3 fatty acids + glycerol Structure of a Triglyceride  Fatty Acids Organic acids (chain of carbons with hydrogen attached) that have acid group at one end & a methyl group at the other end  Fatty Acids Most common components of lipids Exist as esters on different classes of lipids In humans FFAs are formed only during metabolism FAs are aliphatic carboxylic acids with general structure of R--COOH  Hydrogenation: UFA can be converted,. to SFA Halogenation:UFA react with halogens such as l2 3. Melting point: increases with increase in chain length. Short and medium chain have lower melting point than long chain f Salt formation: UFA & SFA can form salts (soaps) with Na ,K, Ca or Mg  Ester formation: UFA & SFA react with alcohol especially glycerol to form esters Glycerol + FA - monoacyl glycerol Monoacyl glycerol + FA - diacyl glycerol Diacyl glycerol + FA - triacy!glycerol 6. Oxidatio FA undergo oxidation to n: can generat in ~-oxidation. But UFA e energ y can.> undergo auto-oxidation due to C=C - rancidity Classification of FAs Common FAs and their characteristics as above as above as above as above as above as as above above as above Common FAs and their characteristics Saturated fatty – Carbon chains acid filled with hydrogen atoms (i.e. no double bond). Saturated fats appear solid at room temperature. Examples: acetic acid, palmitic acid, butyric acid & stearic acid  Saturated FA (SFA) Carbon chains filled with H atoms (i.e. no double bond) Have general formula CH3-(CH2)n-COOH Appear solid at room temperature Examples: Acetic acid CH3-COOH Butyric acid CH3-(CH2)2-COOH Palmitic acid CH3-(CH2)14-COOH Stearic acid CH3-(CH2)16-COOH  Saturated FA (SFA) Acetic and butyric acids are important metabolic intermediates The palmitic and stearic acids are most abundant in body fat Human body fat consists of 50% oleic, 25% palmitic, 10% linoleic and 5% stearic Carbons are numbered 1,2,3… starting from COOH or ω1, ω2, ω3…. Starting from CH3 group  Unsaturated FA (UFA) They have C=C double bond Liquid at room temperature The higher the C=C bonds the more liquid they are Are similar to saturated FAs by reaction at COOH group but exhibit isomerism at C=C Naturally exist as cis isomers, but during metabolism trans isomers may be formed  They could be MUFA or PUFA  Unsaturated FA (UFA) Oleic acid – 18-carbon, monounsaturated Polyunsaturated FA  Location of double bonds Omega number – refers to the position of double bond nearest the methyl (CH3) end of the carbon chain Example is seen in 2 essential PUFAs Omega-3 fatty acid Omega-6 fatty acid FA composition of some common Oils  Omega-3 Vs Omega-6 Fatty Acids Carbons are numbered 1,2,3 starting from COOH end, and Omega 1,2,3 starting from omega carbon (CH3) end  Essential Fatty Acids Linolenic and Linoleic acids are essential FAs because they cannot be synthesized by the body Arachidonic acid – a semi essential FA, becomes essential only when its’ precursor (linoleic acid/Omega-6 FA) is not provided  Functions of essential FAs As components of phospholipids in the cell membrane Synthesis of eicosanoids (potent hormone like chemicals such as PGs & leukotrienes)  Omega-3 produce eicosanoids that lowers  BP by regulating SMs contraction  Omega-3 eicosanoids decreases blood clotting & viscosity, thereby reducing the risk of CHDs,  Arthritis & cancer Copyright 2005 Wadsworth Group, a division of Thomson Learning Hydrogenation of PUFA  Advantag e  Hydrogenation produces more chemically stable fats in food industries that resists oxidation and rancidity (i.e. increase food shelf life). Processing of margarine, peanut butter, baked goods & Snacks  Disadvantag e: - Generation of less healthy trans-fats which LDL-C raises (bad cholesterol) possibly by decreasing the LDL receptor activity thereby increasing the risk of developing CHDx  Cis Vs Trans Fats In nature, most double bonds are cis; meaning that hydrogens next to the double bonds are on the same side of the carbon chain When a fat is partially hydrogenated, some of the double bonds change from cis to trans Cis Vs Trans Fats Copyright 2005 Wadsworth Group, a division of Thomson Learning Copyright 2005 Wadsworth Group, a division of Thomson Learning Comparing Butter & Margarine Labels Cutting Fat Cuts Calories and Saturated Fat Copyright 2005 Wadsworth Group, a division of Thomson Learning Heart-Healthy Choices Copyright 2005 Wadsworth Group, a division of Thomson Learning Dietary Recommendations 1. Use all fats in moderation *1 tsp fat = 5 gm = 45 kcals 2. Beware of “hidden fats” – added to convenience foods, processed foods, & in cooking 3. Choose lean meats, skinless poultry, nonfat dairy products; limit meats to