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Lipids are a heterogenous group of organic compounds which include fats and their derivatives. The main components of lipid are carbon, hydrogen and oxygen compounds are insoluble in water, contain large proportion of carbon-hydrogen bonds and release maximum energy when break down.Fatty acids are organic acids made up of long hydrocarbon chain with a terminal carboxyl group (-COOH). These acids are represented chemically as R- COOH where R may be simple or complex hydrocarbon chain represented as CH3 (CH2) n –COOH. Further, fatty acids may be saturated or unsaturated depending on absence or presence of one or more double bonds between the carbon atoms of hydrocarbon chain. In higher plants the fatty acids present in the fats contain 12 to 26 carbon atoms.

During fat synthesis, three molecules of same or different fatty acids unite with a molecule of glycerol to form a molecule of fat or triglyceride. Hydroxyl groups of glycerol react with carboxyl group of fatty acids and form ester bond by releasing three water molecules.Although there is no single common structure for lipids, the most commonly occurring class of lipids are triglycerides, which are fats and oils. Trigylcerides have a glycerol backbone bonded to three fatty acids. If the three fatty acids are identical then the triglyceride is termed a simple triglyceride. Otherwise, the triglyceride is called a mixed triglyceride.

The second most abundant class of lipids are the phospholipids, which are found in animal and plant cell membranes. Phospholipids also contain glycerol and fatty acids, plus the contain phosphoric acid and a low-molecular-weight alcohol. Common phospholipids include lecithins and cephalins.


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