Lipid Chemistry Lecture Notes PDF

Lipid Chemistry  What are lipids ? Organic compounds insoluble in water (hydrophobic), contain C,H,O but less O2 than in Carbohydrates. Functions :  Mechanical protection  Thermal insulation under skin  Electrical insulation around nerves ...

Lipid Chemistry  What are lipids ? Organic compounds insoluble in water (hydrophobic), contain C,H,O but less O2 than in Carbohydrates. Functions :  Mechanical protection  Thermal insulation under skin  Electrical insulation around nerves  Cell membrane structure  Steroid hormones  Energy storage Classification of Lipids ??  Fatty Acids They are monocarboxylic acids (R- COOH) with: 1- Hydrocarbon chain (R): hydrophobic 2- Carboxyl group (–COOH ): that ionize to –COO- (hydrophilic) so, Fatty acid is an amphipathic molecule i.e. it have both hydrophilic & hydrophobic regions on the same molecule - Long chain Fatty acids are highly water-insoluble. - So, a fatty acid must be transported in blood with a protein ( albumin). - Usually contain even number of carbon atoms.  Classification of Fatty Acids in Nature (according to saturation) 1- Saturated Fatty Acids: no double bonds important examples: Butyric acid: (4C): CH3 - CH2 - CH2 - COOH 4:0 Palmitic acid (16 C): CH3 - (CH2)14 – COOH 16:0 Stearic acid (18C): CH3 - (CH2)16 - COOH 18:0 2- Unsaturated Fatty Acids: They contain one or more double bonds The most important: Oleic acid (18C) : contains one double bond between C9 & C10 in the chain CH3-(CH2)7-CH=CH-(CH2)7-COOH 18:1(9) w9 ( from the methyl carbon end) Linoleic acid (18 C): contains two double bonds between C9 & C10 and C12 & C13 CH3-(CH2)4-CH=CH-CH2-CH=CH-(CH2)7-COOH 18:2(9,12) w6 Linolenic acid (18 C): contains three double bonds between C9-10 , C12-13 & C15-16 CH3-CH2-CH=CH-CH2-CH=CH-CH2-CH=CH-(CH2)7-COOH 18: 3 (9,12,15), w3  Essential Fatty Acids (PUFA) can NOT be synthesized in human body. So, MUST be supplied with food. Two fatty acids are dietary essential in humans: 1- Linoleic acid: w6: precursor of arachidonic acid which is important for prostaglandin synthesis 2- a-Linolenic acid: w3: precursor for other w3 (omega3) fatty acids which are important for growth , development , and protection from heart problems and  1- Simple lipids Natural fats or: (Triglycerides T.G, Triacylglycerols TAG) They are esters of 3 fatty acids with the tri-hydroxy alcohol glycerol = Triacylglycerol They include two types: Solid at ordinary temperature: FATs Liquid at ordinary temperature: OILs Occurrence of neutral fat: 1- in plants: e.g. oils of cotton seed, olive, palm oil, coconut ….etc 2- in animals: e.g. butter, 3- in marine oils: e.g. oils of sea animals as cod liver oil. Conjugated lipids : 1- Phospholipids (PL)  They are important for : 1-Structure of cell membrane 2-Helps triglycerides(TG) absorption in small intestine 3-Lecithin act as lipotropic factor 4-Lecithin is a component of lung surfactant 5-Cardiolipin is used in detection of syphilis. 6-Sphingophospholipids act as electrical insulator (myelin sheath). Conjugated lipids: 2- Glycolipids Conjugated lipids : 3- Plasma Lipoproteins Plasma lipoproteins are spherical macromolecular complexes of lipids and proteins (apoproteins, apolipoproteins) lipoproteins function to transport lipids in plasma They include: chylomicrons, very low density lipoproteins (VLDL), low density lipoproteins (LDL), high density lipoproteins (HDL) 1- Chylomicrons: lowest in density & largest size. highest % of lipid & the lowest % of protein 2- VLDLs & LDLs : denser, having higher ratios of protein to lipid than chylomicrons 3- HDL : the densest as it contains the highest level of protein to lipid in all lipoproteins  Functions of plasma lipoproteins 1. Chylomicrons: They carry exogenous dietary lipids (TG mainly) from intestine to peripheral tissues. 2. Very low density lipoproteins (VLDL): they carry endogenous lipid (TG mainly) from the liver to extrahepatic tissues. 3. Low density lipoproteins (LDL): they transfers cholesterol from blood to tissue (originated from VLDL in blood). 4. High density lipoproteins (HDL): HDL takes cholesterol from peripheral tissues and transfers it to liver. Derived lipid: Steroids: Cholesterol It is the major sterol in animal tissues It is available in cells of the body and in blood Most plasma cholesterol is in esterified form (bound with a fatty acid ). Free cholesterol & esterified cholesterol in blood is transported with a protein in lipoproteins Blood cholesterol level is normally 150-200 mg/dl High cholesterol levels in blood (HYPERCHOLESTEROLEMIA) may lead to ATHEROSCLEROSIS (i.e. deposition of cholesterol on inner walls of blood vessels)  Sources of cholesterol: 1- Diet: in animal sources 2- Synthesis: by liver cells & others Excretion of cholesterol: cholesterol is excreted in bile BUT NOT excreted in urine Functions of Cholesterol 1- Cholesterol enters in the structure of cell membrane, 2- Cholesterol is the precursor for vitamin D3 3- Cholesterol is the precursor of steroid hormones 4- Cholesterol is the source of bile acids & salts which are essential for the digestion and absorption of lipids in the intestine