The other three are derivatives of stearic acid. There are several regularities in the chemistry of these unsaturated fatty acids. First, they contain cis double bonds. Second, the double bonds are always isolated from each other by a CH 2 group. These lipids have been known by a variety of names, including fat , neutral fat , glyceride , triglyceride , and triacylglycerol .
Most animal fats are complex mixtures of different triglycerides.
As the percentage of unsaturated fatty acids increases, the melting point of these triesters decreases until they eventually become an oil at room temperature. Beef fat, which is roughly one-third unsaturated fatty acids, is a solid. Thus, the introduction of unsaturated fatty acids into a triglyceride increases the fluidity of the lipid. They are a far more efficient storage system than carbohydrates such as glycogen or starch because they give off between two and three times as much energy when they are burned. This explains why the seeds of many plants are relatively rich in oils, which provide the energy the seed needs to grow until the leaves can begin to produce energy by photosynthesis.