Biological functions

Proteins have several functions. Some of them are structural components (e.g. keratin in hair, actin, and myosin in muscle, etc.). Many proteins are enzymes. They catalyze various biochemical reactions and therefore are essential to metabolism. Other vital roles of proteins in biological systems are as follows: as transporters (e.g. hemoglobin), as antibodies, and as regulators of gene expression. Not all proteins are biosynthesized de novo. They may be acquired through diet. In fact, animals require a protein diet to obtain the essential amino acids that they cannot synthesize on their own. Thus, in this regard, dietary proteins serve as a food source.