Proteins perform nearly every function carried out by the body on a cellular level. All proteins are built from the same 20 amino acids, and the function of the protein derives from is physical shape in three dimensions. According to About.com, most proteins act in one of seven ways: as antibodies, contractors, enzymes, hormones, storage, structural supports and transporters.
Antibodies and hormones exert a direct chemical influence over the way the body works. Antibodies act against invasive organisms. Hormones, such as testosterone and adrenaline, carry messages throughout the body. Contractile and structural proteins, such as myelin and elastin, build structures in the body and perform work by changing their shape in response to alterations in the surrounding chemical environment. Enzymes work as catalysts to inhibit or accelerate chemical reactions inside cells. Some, such as pepsin, aid digestion. According to About.com, storage proteins such as ovalbumin, which is found in egg whites, collect and keep amino acids by working like microscopic baskets or cages. Transport proteins carry necessary chemicals around the body. Hemoglobin, for example, carries oxygen from high-concentration areas in the lungs to the low-oxygen cell beds. Other transport proteins, such as cytochromes, are crucial to the body's metabolism and act as electron carriers.