Dictionary of Biological Psychology
(from Greek, proteios: primary) A protein is a complex MOLECULE, composed of various combinations of any of the twenty AMINO ACIDS (each made of carbon, hydrogen, oxygen and nitrogen) with a side chain, usually containing sulphur and often phosphorous. Approximately half the dry weight of any animal CELL is made of proteins, which are critical for a range of functions including structure, transport and signalling—a neurotransmitter RECEPTOR for example consists of protein molecules embedded in a neuronal MEMBRANE.
Proteins are the product of GENE activity (see DNA).
Proteins are a class of nutrients, separate from CARBOHYDRATES and FATS or LIPIDS, which consist mainly of amino acids. Many of the twenty amino acids in humans can be produced by the body itself out of other compounds. However, nine amino acids cannot be manufactured by the human body. These types must be obtained in food, and are called ESSENTIAL AMINO ACIDS for that reason: they are essential in any diet.
See also: peptides; polypeptides
KENT C.BERRIDGE
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