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. classification classification of lipids Simple Lipids Conjugated Lipids Derived Lipids Natural fatswaxes Phospholipids Galactolipids lipoproteins Substances obtained by hydrolysis of lipids

4. Natural fats or: (Triglycerides, Triacylglycerols) Simple lipids Natural fats or: (Triglycerides, Triacylglycerols) 3fatty acids glycerol They are esters of 3 fatty acids with the tri-hydroxy alcohol glycerol They include two types: FATs Solid at ordinary temperature: FATs OILs Liquid at ordinary temperature: OILs Occurrence of neutral fat: plants 1- in plants: e.g. oils of cotton seed, olive, lin seed, palm oil, coconut ….etc animals 2- in animals: e.g. butter, lard etc marin oils 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 fatty acids & glycerol CH2R1-COCH2-C-R1 CH2- OH R1-COOH CH2-C-R1 I I -3 H2O I CH2R2-COCH - C - R2 CH2 – OH + R2-COOH CH - C - R2 I I I CH2R3-COCH- C- R3 CH2 – OH R3-COOH CH- C- R3 Triacylglycerol GLYCEROL + 3 molecules of fatty acids Triacylglycerol O O O

6. Chemistry of Fatty Acids monocarboxylic acids (R- COOH) They are monocarboxylic acids (R- COOH) with: Hydrocarbon chain (R): hydrophobic 1- Hydrocarbon chain (R): hydrophobic Carboxyl group (–COOH ): (hydrophilic) 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 i.e. it have both hydrophilic & hydrophobic regions on the same molecule

7. Saturated Fatty Acids 1- Saturated Fatty Acids: contain even number of carbon atoms with no double bonds general formula Cn H2n+1 COOH important examples : Butyric acid4C Butyric acid: (4C): CH 3 - CH 2 - CH 2 - COOH 4:0 Palmitic acid 16 C Palmitic acid (16 C): CH 3 - (CH 2 ) 14 – COOH 16:0 Stearic acid 18C Stearic acid (18C): CH 3 - (CH 2 ) 16 - COOH 18:0 Classification of Fatty Acids in Nature (according to saturation)

8. 2- Unsaturated Fatty Acids: 2- Unsaturated Fatty Acids: They contain even number of carbon atoms and one or more double bonds The most important: Oleic acid 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 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 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) Classification of Fatty Acids according to saturation (cont.)

9. Essential fatty acids Essential fatty acids: can NOT be synthesized in human body can NOT be synthesized in human body. MUST be supplied with food. So, MUST be supplied with food. Two fatty acids are dietary essential in humans: Linoleic acid Linoleic acid: precursor of arachidonic acid which is important for prostaglandin synthesis  -Linolenic acid  -Linolenic acid : precursor for other w3 (omega3) fatty acids which are important for growth and development Essential Fatty Acids

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

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 A hydrophilic head Long hydrophobic Tail

12. Phospholipids & Glycolipids

13. Cholesterol

14. It is the major sterol in animal tissues cells of the body blood It is available in cells of the body and in blood esterified form Most plasma cholesterol is in esterified form (bound with a fatty acid attached to C-3). Free cholesterol & esterified cholesterol liopoproteins Free cholesterol & esterified cholesterol in blood is transported with a protein in liopoproteins 150-250 mg/dl Blood cholesterol level is normally 150-250 mg/dl HYPERCHOLESTEROLEMIA ATHEROSCLEROSIS High cholesterol levels in blood (HYPERCHOLESTEROLEMIA) may lead to ATHEROSCLEROSIS (i.e. deposition of cholesterol on inner walls of blood vessels) Cholesterol Cholesterol (cont.)

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

16. Functions of Cholesterol structure 1- Cholesterol enters in the structure of cell membrane, brain, liver & other organs vitamin D3 2- Cholesterol is the precursor for vitamin D3 steroid hormones 3- Cholesterol is the precursor of steroid hormones source of bile acids & salts 4- Cholesterol is the source of bile acids & salts which 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 lipids proteins lipids and proteins (apoproteins, apolipoproteins) They include: chylomicrons, very low density lipoproteins (VLDL), very low density lipoproteins (VLDL), low density lipoproteins (LDL) low density lipoproteins (LDL) high density lipoproteins (HDL) 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. lipoproteins are composed of lipids & proteins: a neutral lipid core of hydrophobic lipid 1 - a neutral lipid core of hydrophobic lipid (containing triacylglycerol and cholesterol esters) surrounded by a shell of amphipathic lipids 2 - surrounded by a shell of amphipathic lipids (phospholipids & nonesterified cholesterol) Then, the outermost layer is amphipathic apolipoprotein (protein) 3 - Then, the outermost layer is amphipathic apolipoprotein (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) Structure of Plasma Lipoproteins

20. Size & Density of Plasma Lipoprotein Particles Chylomicrons 1- Chylomicrons lowest in density & largest size of all lipoproteins contains the highest percentage of lipid & the lowest percentage of protein VLDLs & LDLs 2- VLDLs & LDLs are denser, having higher ratios of protein to lipid than chylomicrons HDL 3- HDL the densest as it contains the highest level of protein to lipid in all lipoproteind Plasma lipoproteins can be separated lipoprotein electrophoresis - on the basis of their electrophoretic mobility (lipoprotein electrophoresis)

21. Plasma Lipoprotein Electrophoresis

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