Fig. 1

Structural classification of lipids in biological systems. Presented here are the broad lipid classes of fatty acids, glycerolipids, glycerophospholipids, sphingolipids and sterols, and their main sub-classes, along with representative structures. Fatty acids (shown in blue) form the core of most lipid classes and are highly variable with differing chain lengths and saturation. Fatty acids with no double bonds, one double bond and multiple double bonds are further classified into saturated fatty acids, monounsaturated fatty acids, and polyunsaturated fatty acids, respectively. Glycerolipids are formed on addition of fatty acids to a glycerol backbone, while glycerophospholipids have additional phosphate and head groups added. Sphingolipids contain a sphingosine backbone attached with a fatty acid chain. Sterols are tetracyclic ring structures. Glycerol backbone, sphingosine backbone, phosphate group, glycerophospholipid head groups and sterol rings are colored orange, black, light green, purple, and dark green, respectively