Lipids Lecture IV 2022 .pptx

Biochemistry I BCHM101 Lipids Lecture IV 1  Lipids Lipids : The word lipid comes from the Greek lipos, which means “fat.” Lipids are naturally occurring organic compounds. Lipids are a heterogeneous group of organic compounds. They are insoluble in water and soluble in...

Biochemistry I BCHM101 Lipids Lecture IV 1  Lipids Lipids : The word lipid comes from the Greek lipos, which means “fat.” Lipids are naturally occurring organic compounds. Lipids are a heterogeneous group of organic compounds. They are insoluble in water and soluble in organic solvents such as ether and cholorform, benzene..etc. 2  Lipids  Because Compounds are classified as lipids on the basis of a physical property— their solubility—rather than on the basis of their structures, lipids have a variety of structures and functions. 3  Lipids Bloor’s criteria : Lipids are compounds having the following characteristics : They are insoluble in water.  Solubility in one or more organic solvents, Such as ether , choloroform , benzene , acetone ( fat solvents).  Some relationships to the fatty acids as esters either actual or potential.  Possibility of utilization by living organisms. 4  Lipids Biological significance /functions of lipids: They provide energy as diet lipids supply 20-25% of the caloric requirements. It yields more energy than carbohydrates : 9.5 Calorie/g compared to 4 calorie /g for carbohydrates. Lipids play an important role in the diet by helping the absorption of fat soluble vitamins i.e. A,D,E,K. They contain essential fatty acids which maintains normal growth. Lipids present in subcutaneous tissue and around certain organs act as insulating material thus preserving body 5  Lipids ological significance /functions of lipids:  Lipids around internal organs like kidney , etc. may provide padding and protect organs.  Lipids are found in nervous tissue and represents important structural constituents of the nervous tissue.  Lipids in the form of lipoproteins are important cellular constituents occurring in the cell membrane.  Lipoproteins also help in the transportation of lipids in blood such as triacylglycerols, cholesterol and phospholipids. 6  Lipids Classification of lipids: Lipids Compound or conjugated Simple lipids Derived lipids lipids (Esters of fatty acids Fatty acids, alcohols with Various alcohols) Glycerol, sterols Waxes Phospholipids Glycolipids sulpholipids Lipoproteins Fats and (esters of fatty Acids with long chain Oils Aliphatic alcohols (Esters of fatty Cerbrosides Gangliosides Cytolipins acid And glycerol Phosphatidic Lecithins Cephalins Plasmalogens Sphingomyelins acids 7 Lipids Simple lipids 8 Lipids I. Simple lipids: These are esters of fatty acids with various alcohols. a. Neutral fats (Triacylglycerol, TG): are triesters of fatty acids with glycerol. b. Waxes: are esters of fatty acids with monohydroxy aliphatic alcohols other than glycerol. c. True waxes are esters of higher fatty acids with cetyl alcohol (C16H33OH) or other higher straight chain alcohols. d. Cholesterol esters are esters of fatty acid with cholesterol. e. Vitamin A and vitamin D esters are palmitic or stearic acid esters of vitamin A (retinol) or vitamin D respectively. 9 Lipids 10  Lipids II-Compound lipids:  These are the esters of fatty acids with certain other compounds (groups) in addition to glycerol and fatty acids. These include : Phospholipids :lipids +phosphate groups Glycolipids : lipids+carbohydrates Sulpholipids: lipid+ sulphate 11  Lipids 2- Glycolipids : They are lipid containing carbohydrate moiety. They contain a special alcohol called sphingosine and nitrogenous base in addition to fatty acids but does not contain phosphoric acid or glycerol. Their types: a- cerebrosides b-gangliosides c-cytolipins 12  Lipids 3- Sulpholipids: they are lipids characterized by possessing sulphate groups. 4- Lipoproteins: These are complex compounds made up of two moieties i.e. lipids and proteins 13 Lipids Phospholipi ds 14  Lipids Phospholipids :lipids +phosphate groups b- Functions of phospholipids: 1- Structural: Phopspholipids participate in the lipoprotein complexes which are thought to constitute the matrix of cell walls and membranes , the myelin sheath and such structure as mitochondria. 2- Role in enzyme action : certain enzymes require tightly bound phospholipids for their action. Eg. Mitochondrial enzyme system involved in oxidative phosphorylation. 3- Role in blood coagulation: phopholipids play an essential role in blood coagulation process. 15  Lipids 4- Role in lipid absorption in intestine: lecithin lowers the surface tension of water and aids in emulsification of lipid mixtures, a prerequisite in digestion and absorption of lipids from gastrointestinal tract. 5- Role in transport of lipids from intestine: Exogenous triacylglycerol (TG) is carried as lipopreotien complex ,chylomicrons in which Phospholipids (PL) takes active part. 16 Lipids 6. Role in transport of lipids from the liver: Endogenous TG is carried from liver to various tissues as lipoprotein complex VLDL, and PL is required for the formation of this lipoprotein complex. 7. Lipotrophic action of lecithin: Choline acts as a lipotrophic agent as it prevents formation of fatty liver. As lecithin can provide choline it acts as a lipotrophic agent. 8. Role in the mechanism of secretion : phospholipids , especially phosphatidic acid and phosphoinositides turnover is proportional to the rate of secretion of cells liberating such products as hormones, enzymes, mucins and other proteins. 17 Lipids 10- Membrane phospholipids as a source of arachidonic acid: phospholipids of the cell membrane are hydrolysed by the enzyme phospholipase A2 and provide the unsaturated fatty acid arachidonic acid which is utilized for the synthesis of prostaglandins and and leukotrines. 11- insulation : phospholipids of the myelin sheaths provide the insulation around the nerve fibers. 12- Cofactor: Phospholipids are required as a cofactor for the activity of the enzyme lipoprotein lipase and triacylglycerol lipase. 18  Lipids 1) Phospholipids: A) Lecithins:  (Glycerol, saturated fatty acid, unsaturated fatty acid, phosphoric acid, choline).  Lecithins (phosphatidyl cholines) are widely distributed in brain, liver, cardiac muscles 19  Lipids B) Cephalin: These phospholipids contains : 1-Glycerol 2-Saturated fatty acid (R1) 3-Unsaturated fatty acid (R2) 4- Phosphoric acid 5- ethanolamine (CH2 CH2 NH2) Cephalins are present in brain, erythrocytes and many other tissues 20 Lipids C) Plasmalogens A plasminogen molecule is formed of: 1- Glycerol 2-Unstaurated aldehyde 3- Unsaturated fatty acid 4- Ethanolamine (or Choline) 5- Phosphoric acid Plasmalogens are present in large quantities in the skeletal and cardiac muscles 21  Lipids D) Sphingomyelines: They do not contain glycerol but sphingosine 1-They also contain Choline 2-One fatty acid 3-Phosphoric acid 4-Fatty acids usually found in sphingomyelins are palmitic, stearic, lignoceric or nervonic acid 4-They are found in brain, liver, blood and cardiac muscles. 22 23