Lipids are a group of organic compounds found in living organisms. They vary in their structures and functions. Because of their hydrophobic and non-polar nature, lipids are soluble in organic solvents. Lipids are primarily made up of hydrocarbon chains connected to glycerol via ester linkage.

Lipids broadly classify  into two categories–simple lipids and compound lipids. 

Various types of lipids are included within these two major categories of lipids. These include fats, triacylglycerols, wax, phospholipids, steroids, etc. Fatty acids are obtained as a result of hydrolysis of fats. Naturally occurring fatty acids are generally synthesised from two carbon units and hence, contain even number of carbon atoms. Synthesised from 2 carbon units, fatty acid chains may be saturated (having no double bonds) or unsaturated (having one or more double bonds)

Fatty acids are denoted by total number of carbon followed by colon (:) and then total number of double bonds with (delta) having superscript number defining the position of the double bond in parenthesis. For example a fatty acid with 18 carbon with two double bonds between C-9 and C-10 and C-12 and C-13 will be denoted as 18:2 (Δ9,12). 

Unsaturated fatty acids are of two types based on the degree of unsaturation as follows: Monounsaturated fatty acids: ‘Mono’ means single. Therefore, monounsaturated fatty acid contains only a single double bond. for example, oleic acid

Polyunsaturated fatty acids: As the name suggests, these fatty acids contain more than one double bond. e.g., Linoleic acid contains two double bonds, Linolenic acid contains three double bonds; and Arachidonic acid contains four double bonds.

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