LIPIDS

Lipids are the main way that animals store energy. Lipids release more energy per gram than any other class of biological compounds. Fatty acids are basic building blocks of lipids. They are a chain of carbon atoms with a special chemical structure, called a carboxyl group (abbreviated as -COOH) at one end.

Fatty acids are either saturated or unsaturated. Unsaturated fatty acids are liquids (or oils) at room temperature (like Canola oil or corn oil). They also have double bonds rather than single bonds between carbon atoms. Saturated fatty acids have only single carbon to carbon bonds and they are solids at room temperature (like butter, or bacon grease). The lipids that animals use to store energy are called triglycerides. They contain three fatty acids joined to one glycerol (has only 3 carbon atoms plus 5 hydrogen and 3 oxygen atoms) molecule.

This animation (Audio - Important) illustrates triglyceride formation.

Moving up one step in complexity, we have the phospholipids. They are composed of two fatty acids, a phosphate group, and a glycerol molecule. Phospholipids are very important in the formation of the lipid bilayer cell membrane that we will discuss in the next lecture. The cell membrane consists of two layers of phospholipids plus protein. A phosphate group is another example of what is called a functional group. It consists of a phosphorus atom and four oxygen atoms. One end of a phospholipid is hydrophobic (doesn't like water). The other end is hydrophilic (water-loving).

Steroids are an even more complex type of lipid. They have four rings of carbon to which are attached other atoms. Cholesterol (forms plaque on the walls of your arteries), sex hormones (such as testosterone ), and corticosteroids (such as the anti-itch cortisone creme you can buy at the drugstore) are examples of steroids.

REVIEW: Triglycerides are
Answer fats