What is Lipids? eExplain its functions?
Lipids are a group of molecules that are insoluble in polar solvents such as water but soluble in non-polar solvents such as benzene and ether. Lipids contain relatively long hydrocarbon chains that are non-polar and thus hydrophobic. They are divided into three types- simple, compound and derived.
Simple lipids are esters of fatty acids with certain alcohols. They are further of two types - neutral or true fats and waxes.
Neutral or true fats are composed of carbon, hydrogen, and oxygen. A fat molecule consists of two components - one a molecule of glycerol and one to three molecules of long-chain fatty acids.
A glycerol molecule has 3 carbons, each bearing a hydroxyl group (—OH). Fatty acids may be saturated and unsaturated. Saturated fatty acids have higher melting points and are solid at normal temperature. While unsaturated fatty acids have lower melting points and are liquid at normal temperature.
Waxes are lipids composed of long-chain saturated fatty acids and a long chain saturated alcohol of high molecular weight instead of glycerol, e.g., beewax, lanolin, etc.
Complex lipids are derivatives of simple lipids containing additional groups such as phosphate, a nitrogenous base, protein, etc.
They are further divided into the following types :
- Phospholipids: They contain phosphoric acid and frequently a nitrogenous group, in addition to alcohol and fatty acids.
- Glycolipids: These lipids contain a fatty acid, carbohydrate, and nitrogenous base.
- Lipoproteins: These are macromolecular complexes of lipids with proteins.
- Other complex lipids: Sulfolipids, amino lipids, and lipopolysaccharides.
Derived lipids are the derivatives obtained on the hydrolysis of group 1 and group 2 lipids, e.g., steroids, prostaglandins, etc.
Functions of Lipids
Fats serve as food reserves in both plants and animals.
In seeds and spores, lipids help in thermal insulation, protection from ultraviolet radiations and loss of water.