Lipids are very chemically diverse compunds which all share one common trait -- hydrophobia.
They possess little or no affinity to water because of their molecular structure - mostly hydrocarbon
regions with nonpolar bonds. There are three major categories of lipids:
-large molecules composed of the two smaller molecules glycerol and fatty acids. When these two combine,
the product is a triacylglycerol (or tryglyceride). The major function of fat is to supply a reserve
of energy which is stored in adipose cells.
-similar to fats, but contain two fatty acids and a phosphate group which attaches to the glycerol molecule.
The phosphate group is hydrophilic while the hydrocarbons remain hydrophobic. This structure allows phospholipids
to act as cell membranes inside the body.
-consist of four interconnected carbon rings. Cholesterol, an important steroid, is also a part of cell membranes.