Proteins serve as indispensable constituents of every living cell. They participate in every aspect of cell metabolism. They function in growth, maintenance and repair of cells by their action as enzymes catalyzing metabolic reactions, as structural proteins maintaining the shape of the cell, as hormones regulating cell activities, as antibodies providing a defense mechanism, and as contractile proteins, transport proteins, toxins and components of intracellular structures.
Digestive processes depend upon enzymes from the stomach, intestinal glands and pancreas. Cooking of proteins can also assist is the digestion of proteins.