Protein

Protein molecules are chains of amino acids that play many important roles in living systems. As far as is known, proteins have exited as long as life on earth has existed, and are an essential ingredient in all cells. In vertebrates, including humans, proteins are also an important component of the diet. In most animals, whether carnivores, herbivores or omnivores, there are at least some amino acids, usually taken in the form of proteins, that are essential nutrients.