Chemical Structure of Fats.

http://en.wikipedia.org/wiki/Fat

There are many different kinds of fats, but each is a variation on the same chemical structure. All fats are derivatives of fatty acids and glycerol. The molecules are called triglycerides, which are triesters of glycerol and with two carbon chains (one bonded to the single-bonded oxygen and the other to the main carbon), often formed from the reaction of the carboxylic acid and an organic alcohol). As a simple visual illustration, if the kinks and angles of these chains were straightened out, the molecule would have the shape of a capital letter E. The fatty acids would each be a horizontal line; the glycerol "backbone" would be the vertical line that joins the horizontal lines. Fats therefore have "ester" bonds.

The properties of any specific fat molecule depend on the particular fatty acids that constitute it. Different fatty acids are composed of different numbers of carbon and hydrogen atoms. The carbon atoms, each bonded to two neighboring carbon atoms, form a zigzagging chain; the more carbon atoms there are in any fatty acid, the longer its chain will be. Fatty acids with long chains are more susceptible to intermolecular forces of attraction (in this case, van der Waals forces), raising their melting point. Long chains also yield more energy per molecule when metabolized.

A triglyceride molecule

Example of a natural triglyceride with three different fatty acids. One fatty acids is saturated (blue highlighted), another contains one double bond within the carbon chain (greenhighlighted). The third fatty acid (a polyunsaturated fatty acid, highlighted in red) contains three double bonds within the carbon chain. All carbon-carbon double bonds are cis isomers.