Structure and Classification of Lipids

Lipid: A naturally occurring molecule from a plant or animal
soluble in nonpolar organic solvents.
• Fatty acid: A long-chain carboxylic acid; those in animal fats
and vegetable oils often have 12–22 carbon atoms.
• Waxes are carboxylic acid esters, RCOOR’ ,with long, straight
hydrocarbon chains in both R groups; they are secreted by
sebaceous glands in the skin of animals and perform mostly
external protective functions.
Triacylglycerols are carboxylic acid triesters of glycerol, a
three-carbon trialcohol. They make up the fats stored in our
bodies and most dietary fats and oils. They are a major source
of biochemical energy.
Glycerophospholipids are triesters of glycerol that contain
charged phosphate diester groups and are abundant in cell
membranes. Together with other lipids, they help to control the
flow of molecules into and out of cells.
• Sphingomyelins, amides derived from an amino alcohol
(sphingosine), also contain charged phosphate diester groups;
they are essential to the structure of cell membranes and are
abundant in nerve cell membranes.
• Glycolipids, different amides derived from sphingosine, contain
polar carbohydrate groups; on cell surfaces the carbohydrate
portion is recognized by and connects to intracellular
messengers.