You will learn more about steroids in the physiology section in the second semester. If all 3 OH 's on the glycerol are substituted with FA's, then we have a triglyceride . This is fat . Fats differ according to the exact nature of the FA's that are present. So here again as in the case of polysaccharides, the 3-dimensional structure of the molecule has a lot to do with its physical properties.
Fats are a good example of hydrophobic forces at work.
Just think of a fatty chicken soup with those globules of fat floating on top, out of solution. Fats serve as a storage form of energy. That is, like glycogen or starch, fats can be broken down and used for energy metabolism, as we will see later. Fats are stored in cells called adipocytes. There is a special class of lipids that are related to the fats, but with a significant difference.