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Any of a group of complex organic macromolecules that contain carbon, hydrogen, oxygen, nitrogen, and usually sulfur and are composed of one or more chains of amino acids. Proteins are fundamental components of all living cells and include many substances, such as enzymes, hormones, and antibodies, that are necessary for the proper functioning of an organism. They are essential in the diet of animals for the growth and repair of tissue and can be obtained from foods such as meat, fish, eggs, milk, and legumes.
[French protéine, from Late Greek prōteios, of the first quality, from Greek prōtos, first; see per in Indo-European roots.]
pro′tein·a′ceous (prōt′n-ā′shəs, prō′tē-nā′-), pro·tein′ic (prō-tē′nĭk), pro·tein′ous (prō-tē′nəs) adj.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.