Amino Acids, chemical compounds produced by living organisms. Many amino acids are the structural units of proteins. These compounds are called amino acids because each of them contains at least one amino group (an atom of nitrogen and two atoms of hydrogen bonded together chemically).


More than 150 amino acids have been identified; 22 are known to be “building blocks” of proteins. Protein molecules consist of about 50 to more than 3,000 amino acid molecules linked together. When proteins are digested, they are broken down into their constituent amino acids. Proteins differ from one another because of the kinds, number, and arrangement of their amino acids. also Protein.)

Amino acids are used by the body to make tissues, enzymes, hormones, and other vital body substances, and are necessary for the growth, maintenance, and repair of tissues. Most plants are able to produce all the amino acids they need. Animals cannot manufacture all the amino acids they require and must obtain the remainder from their food.

Amino acids that are not produced by animal bodies but that are necessary for proper nutrition are called essential amino acids. Human beings produce 13 of the amino acids they need. The nine essential amino acids required by humans are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Many amino acids can be obtained in pure form, either by isolating them from proteins or by synthesizing them. They are used as dietary supplements and for experimental studies in nutrition.


Amino acids occur principally in chains consisting of amino acid molecules linked together. A short chain is called a peptide; a long chain, a polypeptide. Some amino acid molecules, however, occur singly or attached to other organic molecules, such as carbohydrates. Pure amino acids are usually colorless, water-soluble crystals.

Amino acids have properties of both bases and acids. Each amino acid molecule contains at least one amino group (NH2) and at least one carboxyl group (COOH). The amino group gives the amino acid its basic properties, and the carboxyl group provides the acidic properties. In most amino acids, these two groups are attached to a central carbon atom. In addition, a hydrogen atom (H) and another atom or group of atoms (R), which varies with each amino acid, are attached to the central carbon atom. Thus, zthe generalized formula for an amino acid is RCH (NH2) COOH. For example, glycine, the simplest amino acid, is HCH (NH2) COOH.