The human body uses proteins for many things, including repairing and building tissues, acting as enzymes, aiding the immune system, and serving as hormones. Each of these important functions requires a slightly different form of protein. In spite of their differences in structure, all proteins contain the same basic sub-components. 

Proteins are one of the four different types of macromolecules, in addition to carbohydrates, lipids, or fats, and nucleic acids, such as DNA and RNA. Macromolecules are large molecules that perform specialized functions inside living organisms. The structural arrangement of a protein molecule will differ in accordance with its function.