Lipid Chemistry PDF

Lipid Chemistry Heba Marey Lecturer of Medical Biochemistry Faculty of Medicine, Minia University  Simple Lipids They are called simple because they are formed only from alcohols and Fatty acids. There are two classes of simple lipids (according t...

Lipid Chemistry Heba Marey Lecturer of Medical Biochemistry Faculty of Medicine, Minia University  Simple Lipids They are called simple because they are formed only from alcohols and Fatty acids. There are two classes of simple lipids (according to the type of alcohol): Acylglycerols are esters of one, two or three fatty acids with glycerol. Waxes are esters of fatty acids with monohydric alcohol higher than glycerol.  Triacylglycerols Waxes These are esters of fatty acids They are called neutral fat because with long chain alcohol other than glycerol. they carry no charge. These alcohols contain one They are stored mainly in (OH) group, i.e., monohydric alcohols e.g. bee wax. cytoplasm of adipose tissue cells They are excreted (which is located subcutaneously extracellularly in some plants and around kidney and other and animals and has a protective function as in Bee wax and organs). Sebaceous secretions.  Complex (Compound) Lipids These are esters of fatty acids with alcohol and an extra group I. Phospholipids: They contain phosphoric acid residues. They are classified into glycerophospholipids (contain glycerol) and sphingophospholipids (contain sphingosine). a) Phosphatidic acid (diacylglycerolphosphate): Structure: Glycerol + Saturated fatty acid attached to position 1, Unsaturated fatty acid attached to position 2 + phosphoric acid residue at position 3. b) Cardiolipin (diphosphatidylglycerol): ✓ It is formed of two phosphatidic acids linked together by glycerol. ✓ It is the major lipid in mitochondrial membrane. ✓ It stimulates antibody formation i.e. antigenic c) Lecithin (phosphatidyl choline): It is formed of Glycerol + Saturated fatty acid attached to 1 position + Unsaturated fatty acid attached to 2 position + Phosphoric acid attached to 3 position + Choline base (attached to phosphoric acid). 1) Lecithin enters in the structure of cell membrane. It is the most abundant phospholipid in cell membrane. 2) Lecithin acts as lipotropic factor i.e. prevent accumulation of fat in liver (fatty liver) and gall cholesterol stones. 3) Dipalmityl lecithin (I.e. lecithin which contains 2 palmitic acid residues) acts as a surfactant in the lung. Respiratory distress syndrome (hyaline membrane disease): In premature babies, lungs do not secrete enough surfactant. This leads to lung collapse and death from respiratory failure. Treatment of this case needs putting the premature babies in Incubator and administration of surfactant locally in the lung. d) Sphingomyelins: It is formed of Sphingosine + Fatty acid (attached to at position 2) + Phosphoric acid residue (attached to 3 position) + Choline base (attached to phosphoric acid). Function: It is present in high concentrations in brain and nerve tissue. Niemann Pick's disease: It is accumulation of large amounts of sphingomyelin in liver due to deficiency of sphingomyelinase enzyme. It leads to mental retardation and death in early life. II. Glycolipids: These are complex lipids containing carbohydrate. They also contain sphingosine (therefore, glycolipids together with sphingomyelin may be classified as sphingolipids). Glycolipids include: Cerebrosides (simple glycolipids): contain sugar usually galactose. They act as insulator for nerve impulse. Ganglioside (complex glycolipids): because they contain in addition to hexose, one or more sialic acid molecules. III. Lipoproteins: These are complex lipids formed of lipids conjugated with protein. They are present in cell membrane, mitochondria and plasma (plasma lipoproteins). Plasma lipoproteins convert water insoluble lipids into water soluble complexes. This facilitates transport of lipids between blood and different tissues.  Derived Lipids Substances which are insoluble in water but soluble in nonpolar solvents. They include: 1. Steroids and sterols. 2. Carotenoids 3. Ketone bodies. 4. Fatty acids.  Steroids Types of steroids and sterols are: 1. Cholesterol (animal origin). 6. Steroid hormones: 2. Ergosterol (plant origin). a) Male sex hormones. 3. Vitamin D group (D2 and D3). b) Female sex hormones. 4. Bile salts. c) Adrenocortical hormones. 5. Digitalis glycosides. 7. Some carcinogenic substances. Cholesterol: It is formed from activated acetate. It acts as a precursor of all steroids in animal body. It is present in every body cell (cell membrane) especially in: 1)Adrenal cortex. 2) Gonads. 3) Liver and kidney. 4) Brain and nerve tissue. 5) Skin and adipose tissue. It is mainly excreted from the body in bile in the form of bile salts, less amounts as cholesterol, cholesteryl esters and dehydrocholesterol. In large intestine, it is reduced by bacteria to give corpostanol.  It occurs in the blood in 2 forms: free form (30%) and esterified form (70%) (combined to fatty acids to form ester). The level of blood cholesterol is normally less than 220 mg/dl. Any increase above this level is called: hypercholesterolemia predisposes to atherosclerosis which leads to hypertension. Function: It is important for: a)It enters in the structure of every body cell particularly cell membranes & in nervous tissue. b)Synthesis of steroid hormones. c)Synthesis of bile salts. d)Synthesis of vitamin D3.