Lipids are important constituents of our diet because of their high energy value. In the body, fats serve as efficient source of energy which is stored in adipose tissues. They also serve as an insulating material in sub¬cutaneous tissues and around certain organs. Fats in combination with proteins are important constituents of cell membranes and mitochondria.
Lipids are a group of organic compounds including fats and fat-like substances. For the first time the term 'lipid' was used by a German biochemist, Bloor, in the year 1943, for a major class of tissue components and foodstuffs. Lipids are widely disseminated throughout the plant and animal kingdom. In plants, they occur in seeds, nuts and fruits; and in animals, they are stored in adipose tissues, bone marrow and nervous tissues. Many substances which we come across in our daily life like cooking oil, butter, ghee, waxes, natural rubber and cholesterol are either lipids or rich in lipids.
In general, lipids comprise a heterogeneous group of compounds which are sparingly soluble in water but show considerable solubility in organic solvents like ether, chloroform, benzene, petroleum ether. On hydrolysis, they yield fatty acids which are utilised by the living organisms. Lipids are the compounds of carbon, hydrogen and oxygen. The number of oxygen atoms in a lipid molecule is always less than the number of carbon atoms. That is why they require more oxygen for their oxidation and release more energy in comparison to carbohydrates. Some lipids also contain small amounts of phosphorus, nitrogen and sulphur.
Lipids are esters of fatty acids. An ester is an organic compound formed of an alcohol and an acid by removal of water, corresponding to salts in inorganic chemistry. Lipids are composed of C, H and O mainly but some of them may also contain phosphorus (P), Sulphur (S) and Nitrogen (N). However, they contain much less Oxygen than carbohydrates. A lipid molecule is basically made up of an alcohol (such as glycerol, cholesterol spyngosine etc.) with the fatty acids. Some of the lipids contain certain oyher constituents to make their molecules more complex.
Chemically, fats are the esters of glycerol and fatty acids or triglycerides of fatty acids as 3 molecules of fatty acids condense with one mole of glycerol to form fat. For example, 3 molecules of palmitic acid on condensation with one molecule of glycerol yield a fat known as tripalmitin.
In general the lipids are of two classes, those are simple lipids and the complex lipids.
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