Chemistry of Compound Lipids PDF

Prof.Dr/ Doaa Mostafa Gharib Assistant professor of Medical Biochemistry – Faculty of Medicine- Cairo University  Lipids These are organic compounds characterized by being: 1- Esters of fatty acids Or substances associated with them in nature. 2- Insoluble in H2O...

Prof.Dr/ Doaa Mostafa Gharib Assistant professor of Medical Biochemistry – Faculty of Medicine- Cairo University  Lipids These are organic compounds characterized by being: 1- Esters of fatty acids Or substances associated with them in nature. 2- Insoluble in H2O but soluble in fat solvents Lipid = fatty acids + alcohol  Classification Simple lipids Compound lipids Derived lipids (conjugated lipids) FA + Alcohol - hydrolysis FA + Alcohol + other group of First two groups  Subclassified according to the type of prosthetic group Phospholipids Glycolipids Proteolipids CHO Phosphate Protein radical FA + ALCOHOL + PHOSPHATE A L C O H O L Phospholipids classified on the basis of the type of alcohol present A. Glycerophospholipids B. Sphingophospholipids ✓ Phosphatidic acid ✓ Phosphatidylcholine ✓ Phosphatidyl ✓ Sphingomyelin ethanolamine ✓ Phosphatidyl serine ✓ Phosphatidyl inositol ✓ Lysophospholipids  A. Glycerophospholipids Derivatives of Phosphatidic acid ?  Phosphatidic acid The precursor (mother substance) of all phospholipids containing glycerol. On hydrolysis, it gives glycerol + 2 F.A. + phosphate.  Phosphatidyl Serine Serine P G Serine 2 F A  Phosphatidyl-Serine Hydrolytic products: - One glycerol - Two FA - Phosphate - Serine  Phosphatidylcholine ( Lecithin) Hydrolytic products: - One glycerol - Two FA - Phosphate - Choline  Phosphatidyl ethanolamine ( Cephalin) Hydrolytic products: - One glycerol - Two FA - Phosphate - Ethanolamine  Phosphatidyl-inositol Hydrolytic products: - One glycerol - Two FA - Phosphate - Inositol Hydrolysis of glycerophospholipids They are hydrolyzed by a group of enzymes termed phospholipases (PLA1, PLA2, PLC and PLD). Phospholipase D is not present in humans, but present only in plants.  Compound Lipids Snake venom toxins Contain lecithinase enzyme with PLA2 activity, when injected into blood, it converts phospholipids present in cell membranes of RBCs into lysophospholipids. Therefore, snake venom toxins produce hemolysis of RBCs, which causes death if not treated by antitoxins. A. Glycerophospholipids B. Sphingophospholipids ✓ Phosphatidic acid ✓ Phosphatidylcholine ✓ Phosphatidyl ✓ Sphingomyelin ethanolamine ✓ Phosphatidyl serine ✓ Phosphatidyl inositol ✓ Lysophospholipids  B. Sphingomyelin Presenst in cell membranes specially of the lungs and brain mainly in the myelin sheath. It contains sphingosine (sphingol) which is an 18 carbon amino alcohol. Fatty acid are linked to sphingosine by an amide bond to form ceramide. When connected to phoshocholine it forms sphingomyelin. B. Sphingomyelin Importance and Functions of Phospholipids 1. They are amphipathic molecules contain non-polar groups (fatty acid side chains) and polar groups (glycerol, phosphate, serine, ethanolamine, choline and inositol) and form micelles in water. 2. Help digestion and absorption of fats (emulsifying factors). 3.They prevent deposition of cholesterol as cholesterol stones (biliarycalculi) (hydrotropic substances). 4. Important constituents of cell membrane (lipid bilayer). 5. Important constituents of plasma lipoproteins. 6. They provide arachidonic acid for synthesis of eicosanoids (hormone like substances). 7. Essential for blood clotting factors as they provide platelet activating factor (PAF). 8. Form lung surfactant (dipalmitoyl-lecithin) and its deficiency causes respiratory distress syndrome in premature infants.. Dipalmityl Phosphatidyl choline = Dipalmityl lecithin LUNG SURFACTANT It decrease the surface tension in the lung alveoli. So, it prevent adherence of the inner surfaces of the lung. At, birth if decrease----- it leads to “RDS” respiratory distress syndrome 9- Sphingomyline is present in cell membranes of the lungs and brain mainly in the myelin sheath.