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Introduction to Lipids

Introduction to Lipids . What are Lipids ??. Lipids are organic compounds which are related to fatty acids Lipids are insoluble in water & soluble in nonpolar solvents (fat solvents) such as alcohol, ether, benzene, acetone, chloroform . classification of lipids . Derived Lipids.

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Introduction to Lipids

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  1. Introduction to Lipids

  2. What are Lipids ?? • Lipids are organic compounds which are related to fatty acids • Lipids are insoluble in water & soluble in nonpolar solvents (fat solvents) such as alcohol, ether, benzene, acetone, chloroform

  3. classificationof lipids Derived Lipids Simple Lipids Conjugated Lipids • Phospholipids • Galactolipids • lipoproteins Substances obtained by hydrolysis of lipids Natural fats waxes

  4. Simple lipidsNatural fats or: (Triglycerides, Triacylglycerols) • They are esters of 3fatty acids with the tri-hydroxy alcohol glycerol • They include two types: Solid at ordinary temperature: FATs Liquid at ordinary temperature: OILs • Occurrence of neutral fat: 1-inplants: e.g. oils of cotton seed, olive, lin seed , palm oil, coconut ….etc 2- in animals: e.g. butter, lard etc 3- in marin oils: e.g. oils of sea animals as cod liver

  5. Chemistry of Triacylglycerols Triacylglycerols are esters resulting from the reaction of fatty acids & glycerol CH2- OHR1-COOHCH2-C-R1 I -3 H2O I CH2 – OH + R2-COOHCH - C - R2 II CH2 – OHR3-COOHCH- C- R3 GLYCEROL+3 molecules of fatty acids Triacylglycerol O O O

  6. Chemistry of 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

  7. Classification of Fatty Acids in Nature (according to saturation) 1- Saturated Fatty Acids: contain even number of carbon atoms with no double bonds general formula Cn H2n+1 COOH 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

  8. Classification of Fatty Acids according to saturation (cont.) 2- 2-Unsaturated Fatty Acids: They contain even number of carbon atoms and 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) 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) 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 ( from the methyl carbon end)

  9. Essential Fatty Acids Essential fatty acids: canNOT be synthesized in human body. So, MUSTbe supplied with food. Two fatty acids are dietary essential in humans: Linoleic acid: precursor of arachidonic acid which is important for prostaglandin synthesis a-Linolenic acid: precursor for other w3 (omega3) fatty acids which are important for growth and development

  10. Transport of Fatty Acids in Blood - Fatty acids are highlywater-insoluble - So, a fatty acid must be transported in blood in with a protein 1- Fatty Acid Esters > 90% of blood fatty acids are esters i.e. included in triacylglycerol, in cholesterol esters & in phospholipids that are transported in blood with lipoprotein particles 2- Free Fatty Acids (Unesterified) < 10 of blood fatty acids are free (unesterified) i.e. not bound to any other molecule They are transported in blood with albumin.

  11. Phospholipids PL are conjugated lipids PL are ionic polar structure formed of an alcohol that is attached by bridge to a back bone either diacylglycerol or sphinogosine Long hydrophobic Tail A hydrophilic head

  12. Phospholipids & Glycolipids

  13. Cholesterol

  14. Cholesterol(cont.) • 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 attached to C-3). • Free cholesterol & esterified cholesterol in blood is transported with a protein in liopoproteins • Blood cholesterol level is normally 150-250 mg/dl • High cholesterol levels in blood (HYPERCHOLESTEROLEMIA) may lead to ATHEROSCLEROSIS(i.e. deposition of cholesterol on inner walls of blood vessels)

  15. Cholesterol(cont.) • Sourcesof cholesterol: 1- Diet:in animal sources 2- Synthesis:by liver cells & others • Excretionof cholesterol: cholesterol is excreted in bile BUT NOT excreted in urine

  16. Functions of Cholesterol 1- Cholesterol enters in the structureof cell membrane, brain, liver & other organs 2- Cholesterol is the precursor for vitamin D3 3- Cholesterol is the precursor of steroid hormones 4- Cholesterol is the source of bile acids & saltswhich are secreted with the bile juice & essential for the digestion of lipids in the intestine

  17. Plasma Lipoproteins Plasma lipoproteins are spherical macromolecular complexes of lipidsand proteins(apoproteins, apolipoproteins) They include: • chylomicrons, • very low density lipoproteins (VLDL), • low density lipoproteins (LDL) • high density lipoproteins (HDL) • They differ in lipid & protein composition, in size, density & site of origin • lipoproteins function to keep their component lipids soluble to transport them in plasma

  18. Structure of Plasma Lipoproteins lipoproteins are composed of lipids & proteins: 1 -a neutral lipid core of hydrophobic lipid (containing triacylglycerol and cholesterol esters) 2 - surrounded by a shell of amphipathic lipids (phospholipids & nonesterified cholesterol) 3 - Then, the outermost layer is amphipathicapolipoprotein (protein) • Amphipathic compounds are oriented so that their polar portions are exposed on the surface of the lipoprotein thus making the particle soluble in aqueous solution • The triacylglycerol and cholesterol carried by the lipoproteins are obtained either from the diet (exogenous source) or from de novo synthesis (endogenous source)

  19. Structure of Plasma Lipoproteins

  20. Size & Density of Plasma Lipoprotein Particles 1- Chylomicrons • lowest in density & largest size of all lipoproteins • contains the highest percentage of lipid & the lowest percentage of protein 2- VLDLs & LDLs • are 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 lipoproteind Plasma lipoproteins can be separated - on the basis of their electrophoretic mobility (lipoprotein electrophoresis)

  21. Plasma Lipoprotein Electrophoresis

  22. Functions of plasma lipoproteins • Chylomicrons: They carry dietary lipids (TG & Cholesterol) & fat soluble vitamins to blood. • Very low density lipoproteins (VLDL) is to carry lipid from the liver to tissues. • Low density lipoproteins (LDL) transfers cholesterol from blood to tissues (originated from VLDL in blood). • High density lipoproteins (HDL): HDL takes cholesterol from peripheral tissues and transfers it to liver.

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