Lipids are a varied group of molecules most of which are insoluble in water. Like carbohydrates, carbon, hydrogen, and oxygen are the principal elements of lipids although the oxygen content is much reduced. Fats, phospholipids, steroids, carotenoids, and waxes are lipids. Fats are the most abundant group of lipids in the biological world. Fats are composed of three fatty acid molecules bonded to a molecule of the alcohol glycerol.
Fats have at least twice the energy ,storing capacity per unit weight as carbohydrates do.
Cholesterol is an important steroid that is a part of some hormones. Steroids differ from most other lipids by virtue of the structure of steroids consisting of carbon rings instead of chains. As a result of this they tend to be non-polar and do not dissolve into polar solvents such as water. The fat we will use, like that shown in figure 1A, is a typical fat with three fatty acid chains. Another group of important lipids are the phospholipids.