pro·tein
/'pro?tin, -ti?n/
–noun
1. Biochemistry. any of numerous, highly varied organic molecules constituting a large portion of the mass of every life form and necessary in the diet of all animals and other nonphotosynthesizing organisms, composed of 20 or more amino acids linked in a genetically controlled linear sequence into one or more long polypeptide chains, the final shape and other properties of each protein being determined by the side chains of the amino acids and their chemical attachments: proteins include such specialized forms as collagen for supportive tissue, hemoglobin for transport, antibodies for immune defense, and enzymes for metabolism.
2. the plant or animal tissue rich in such molecules, considered as a food source supplying essential amino acids to the body.
3. (formerly) a substance thought to be the essential nitrogenous component of all organic bodies.