Lipids
Fats, oils, waxes, cholesterol, steroid hormones and Vitamins A and D – all of these
natural products belong to the diverse class of biological compounds called lipids. The
biological functions of lipids are as diverse as their structures. Fats and oils, for
example, are used to store energy within cells and organisms. In addition to acting as
energy sources, fats accumulate in adipose tissue that insulates and protects internal
organs. Phospholipids are responsible for the “lipid bilayer” structures that form
protective membranes around cells. The steroid hormones, which are synthesized in the
body from cholesterol, act as chemical messengers, carrying signals from one part of
the body to another.
Fats and oils – referred to collectively as triglycerides – have the same basic structure.
Triglycerides consist of a glycerol backbone and three attached fatty acid residues.
Fatty acids are long-chain carboxylic acids, consisting of a long hydrocarbon “tail” with a
carboxyl group at one end. Fatty acids range in length from 10 to 20 carbon atoms and
always contain an even number of carbon atoms. The hydrocarbon chains in fatty acids
can be saturated with hydrogen atoms or unsaturated (monounsaturated or
polyunsaturated). Fats are solids and are primarily obtained from animal tissue. Oils are
liquids and are primarily obtained from plants. Olive oil is an example of an oil, while
lard is an example of a fat.
glycerol
+
3 fatty acids

triglyceride
Saturated fatty acid
Monounsaturated fatty acid
Polyunsaturated fatty acid
cis-configuration
trans-configuration