Lipids

LIPIDS Lipids are a large and diverse group of naturally occurring organic compounds that are related by their solubility in nonpolar organic solvents and general insolubility in water. They are formed by condensation reaction between fatty acids and alcohols. Lipids are esters of moderate to long chain fatty acids with alcohols The main biological functions of lipids include energy storage, as structural components of cell membranes, and as important signalling molecules. Lipids are non-polar (hydrophobic) compounds, soluble in organic solvents such as chloroform, methanol.

FATTY ACIDS The lipid building blocks. Fatty acids consist of a hydrocarbon chain with a carboxylic acid at one end. The fatty acid chains are usually between 10 and 20 Carbon atoms long. The fatty "tail" is non-polar (Hydrophobic) while the Carboxyl "head" is a little polar (Hydrophillic). Eg: A 16-C fatty acid: CH 3 (CH 2 ) 14 -COO - Non-polar polar

Fatty Acids The carbon chain of fatty acids may be saturated or unsaturated. Where a double bond exists, there is the possibility of either a cis or a trans geometric isomerism. Most naturally occurring fatty acids are of the cis configuration. Cis and trans-2-butene

Fatty acids Fatty acids are of two types: Saturated : only single bonds between Carbon atoms Unsaturated : contain one or more double bonds. The double bond gives unsaturated fatty acids a bend in the chain. This bend affects the chemical characteristics of unsaturated fatty acids.

Saturated FattyAcids Contain only single C–C bonds Closely packed Strong attractions between chains High melting points Solids at room temperature Eg: Butter, 6

Unsaturated Fatty Acids Contain one or more double C=C bonds Nonlinear chains do not allow molecules to pack closely Few interactions between chains Low melting points Liquids at room temperature Eg: Vegetable oils 7

Some fatty acids and their common names: 14:0 myristic acid 16:0 palmitic acid 18:0 stearic acid 18:1 cis  9 oleic acid 18:2 cis  9,12 linoleic acid 18:3 cis  9,12,15  -linolenic acid 20:4 cis  5,8,11,14 arachidonic acid Most naturally occurring fatty acids have an even number of carbon atoms. Examples of Fatty Acids Naming a Fatty Acid: First digit: No of Carbon atoms Second Digit: No of double bonds    Position of Double bond

Classification of Lipids Based on their functions lipids are classified as Storage Lipids: Triglycerides Membrane Lipids: Phospholipids, Glycolipids

Storage Lipids: Triglycerides The triesters of fatty acids with glycerol compose the class of lipids known as fats and oils. These triglycerides are found in both plants and animals.- they are the simplest lipids Triglycerides that are solid or semisolid at room temperature are classified as fats, and occur predominantly in animals. Those triglycerides that are liquid are called oils and originate chiefly in plants.

Storage Lipids: Triglycerides Triglycerides are Energy-storage molecules. They are formed by connecting three fatty acids to a molecule Glycerol.

Storage Lipids :Waxes Biological waxes are esters of long-chain (C14 to C36) saturated and unsaturated fatty acids with long-chain (C16 to C30) alcohols. In addition to being storage form of metabolic fuel, waxes have other diverse roles: as water- repellent, coating on leave surface to prevent excess evaporation

Membrane Lipids: Phospholipids This class of lipids are really derivatives of triglycerides. They are composed of a glycerol molecule with two fatty acids (a diglyceride). The third carbon contains a phosphate group and usually some added polar molecule (such as ethanolamine, serine or choline)

Membrane Lipids :Phospholipids Major component of all cell membranes as they can form lipid bilayers.

Membrane Lipids:Glycolipids Glycolipids are composed of lipids that are covalently bonded to monosaccharides or polysaccharides. Their role is to provide energy and also serve as markers for cellular recognition.

Sphingolipids Are a class of lipids which are composed of one molecule of long chain alcohol called sphingosine. Instead of glycerol these lipids have Sphingosine. These compounds play important roles in signal transmission and cell recognition

Membrane Lipids: Cholesterol Cholesterol, an important constituent of cell membranes, has a rigid ring system and a short branched hydrocarbon tail. Cholesterol is largely hydrophobic. But it has one polar group, a hydroxyl, making it amphipathic.

SUMMARY