Chemistry of Lipids PDF

Lipid are insoluble in water but soluble in fat solvents (non polar solvents) e.g. benzene, chloroform, acetone and ether) The lipids of physiological importance for humans have four major functions: 1. They serve as structural components of biological membranes. 2. They provide energy reserves, mai...

Lipid are insoluble in water but soluble in fat solvents (non polar solvents) e.g. benzene, chloroform, acetone and ether) The lipids of physiological importance for humans have four major functions: 1. They serve as structural components of biological membranes. 2. They provide energy reserves, mainly in the form of triacylglycerols. 3. Both lipids and lipid derivatives serve as vitamins and hormones. 4. Bile acids and bile salts help in fat emulsification.  Fatty acids are long-chain hydrocarbon molecules containing a carboxylic acid moiety at one end. They have the general formula of R─COOH:  -R: is a hydrocarbon chain which makes fatty acids hydrophobic.  -COOH: this group gives the fatty acids the hydrophilic properties.  amphipathic nature  (i.e. having both a hydrophilic and a hydrophobic region).  According to the presence or absence of double bond, fatty acids are classified into:  Saturated fatty acids  Unsaturated fatty acids  According to the length of the chain, they are either short-chain (from C2 – C10) or long-chain (> C10) fatty acids.  Butyric acid: CH3.CH2.CH2.COOH (C4)(butter)  Palmitic acid: CH3.(CH2)14.COOH (C16)(animal fat)  Stearic acid: CH3.(CH2)16.COOH (C18)(animal fat) Saturated fatty acids of less than eight carbon atoms are liquid at physiological temperature, whereas those containing more than ten are solid. Oleic acid: CH3.(CH2)7.CH═CH.(CH2)7.COOH (C18:1) Linoleic acid: CH3(CH2)3(CH2.CH═CH)2(CH2)7COOH (C18:2) Linolenic acid: CH3(CH2.CH═CH)3(CH2)7COOH (C18:3) Arachidonic acid: CH3(CH2)3(CH2.CH═CH)4(CH2)3COOH (C20:4) - USFA which contain two or more double bonds in their structure are termed PUFA: polyunsaturated fatty acids - In contrast to most fatty acids, linoleic and linolenic acids cannot be synthesized inside the human body, and must be supplied by the diet. Thus, they are termed essential fatty acids.   - Eicosanoids include different groups of powerful hormone like molecules that are produced by most mammalian tissues.  -They are collectively known as eicosanoids to reflect their origin from polyunsaturated fatty acids with 20 (eicosa) carbon atoms, e.g., arachidonic acid.  - Eicosanoids act locally within the cells in which they are produced or on adjacent cells. A- CYCLIC COMPOUNDS ACYCLIC COMPOUNDS -  Prostaglandins (PG)  - Leukotrienes (LT).  - Prostacyclins (PGI)  - Lipoxins (LX)  - Thromboxanes (TX)  1. Prostaglandins - Synthesis: produced by most tissues. - Functions: 1-Promote imflammation. 2-Promote uterine contractions. 3-Produce inhibition of gastric secretion. Some prostaglandins produce vasodilatation (eg. PGE2) while other produce vasoconstriction (eg. PGF2). 2. Prostacyclins - Synthesis: produced by the endothelium of blood vessels. - Functions: produce vasodilatation and inhibits platelet aggregation. 3. Thromboxanes - Synthesis: produced by the platelets. - Functions: produce vasoconstriction and platelet aggregation.  1. Leukotrienes  - Synthesis: produced by the leukocytes, platelets and mast  cells. - They are released during severe allergic reactions.  - Functions: increase vascular permeability and produce  bronchospasm. 