Like sugars, fatty acid molecules are composed of carbon, hydrogen and oxygen atoms. Fatty acid molecules have chains of carbon and hydrogen. These molecules are lipophilic, meaning that they will only mix with other fatty molecules and do not mix with water.
Figure 3.15 Palmitic acid, a fatty acid that has 16 carbon atoms, with associated hydrogen atoms, attached to oxygen atoms. Like the name suggests, this fatty acid is a major component of palm oil, but it also makes up large portions of human fat and breast milk.
Fatty acids can react with other small molecules to form triglycerides or phospholipids. Triglyceride and phospholipid molecules and other derivatives of fatty acids are used in organisms for energy storage. Another function of phospholipids is to form membranes that enclose cells and organelles within the cells.