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Longman Dictionary of Contemporary English
amino acid
noun
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▪ Tryptophan is a naturally occurring amino acid.
Wiktionary
amino acid

n. 1 (context organic chemistry English) Any organic compound containing both an amine and a carboxylic acid functional group. 2 (context biochemistry English) Any of the twenty naturally occurring α-amino acids (having the amino, and carboxylic acid groups on the same carbon atom), and a variety of side chains, that combine, via peptide bonds, to form proteins.

WordNet
amino acid

n. organic compounds containing an amino group and a carboxylic acid group; "proteins are composed of various proportions of about 20 common amino acids" [syn: aminoalkanoic acid]

Wikipedia
Amino acid

thumb|upright=2.0|right|alt=Table of Amino Acids.|The 21 proteinogenic α-amino acids found in eukaryotes, grouped according to their side-chains' pK values and charges carried at physiological pH 7.4

Amino acids are biologically important organic compounds containing amine (-NH) and carboxylic acid (-COOH) functional groups, usually along with a side-chain (R group) specific to each amino acid. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen, though other elements are found in the side-chains of certain amino acids. About 500 amino acids are known (though only 20 appear in the genetic code) and can be classified in many ways. They can be classified according to the core structural functional groups' locations as alpha- (α-), beta- (β-), gamma- (γ-) or delta- (δ-) amino acids; other categories relate to polarity, pH level, and side-chain group type ( aliphatic, acyclic, aromatic, containing hydroxyl or sulfur, etc.). In the form of proteins, amino acids comprise the second-largest component (water is the largest) of human muscles, cells and other tissues. Outside proteins, amino acids perform critical roles in processes such as neurotransmitter transport and biosynthesis.

In biochemistry, amino acids having both the amine and the carboxylic acid groups attached to the first (alpha-) carbon atom have particular importance. They are known as 2-, alpha-, or α-amino acids (generic formula HNCHRCOOH in most cases, where R is an organic substituent known as a " side-chain"); often the term "amino acid" is used to refer specifically to these. They include the 23 proteinogenic ("protein-building") amino acids, which combine into peptide chains ("polypeptides") to form the building-blocks of a vast array of proteins. These are all L- stereoisomers (" left-handed" isomers), although a few D-amino acids ("right-handed") occur in bacterial envelopes, as a neuromodulator (D- serine), and in some antibiotics. Twenty of the proteinogenic amino acids are encoded directly by triplet codons in the genetic code and are known as "standard" amino acids. The other three ("non-standard" or "non-canonical") are selenocysteine (present in many noneukaryotes as well as most eukaryotes, but not coded directly by DNA), pyrrolysine (found only in some archea and one bacterium) and N-formylmethionine (which is often the initial amino acid of proteins in bacteria, mitochondria, and chloroplasts). Pyrrolysine and selenocysteine are encoded via variant codons; for example, selenocysteine is encoded by stop codon and SECIS element. Codon– tRNA combinations not found in nature can also be used to "expand" the genetic code and create novel proteins known as alloproteins incorporating non-proteinogenic amino acids.

Many important proteinogenic and non-proteinogenic amino acids also play critical non-protein roles within the body. For example, in the human brain, glutamate (standard glutamic acid) and gamma-amino-butyric acid ("GABA", non-standard gamma-amino acid) are, respectively, the main excitatory and inhibitory neurotransmitters; hydroxyproline (a major component of the connective tissue collagen) is synthesised from proline; the standard amino acid glycine is used to synthesise porphyrins used in red blood cells; and the non-standard carnitine is used in lipid transport.

Nine proteinogenic amino acids are called "essential" for humans because they cannot be created from other compounds by the human body and so must be taken in as food. Others may be conditionally essential for certain ages or medical conditions. Essential amino acids may also differ between species.

Because of their biological significance, amino acids are important in nutrition and are commonly used in nutritional supplements, fertilizers, and food technology. Industrial uses include the production of drugs, biodegradable plastics, and chiral catalysts.

Usage examples of "amino acid".

He needed a nonhistone fraction whose amino acid sequence would bridge the gap between plant and animal species.

The method used was to break down the amino acid chains only partway by the use of acid or of various enzymes.

He thought of the chilly gun in his belt, under the untucked shirt, and knew he wouldn't be able to drag it free before the Amino Acid had time for at least two shots.

The problem is that words in the amino acid alphabet are often exceedingly long.

A vitamin and mineral tablet, Amino Acid Complex, zinc tablets, and Evening Primrose Oil (500 mg to be taken orally), have been found beneficial in counteracting this complaint.

We're particularly interested because the absence of an enzyme can lead to the absence of a particular amino acid, and a change in one amino acid out of some three hundred of them can result in a fatal condition.

Through a bit of luck I was able to identify the stimulator of the red tide as a most unusual organometallic compound, a combination of a synthetic amino acid and cobalt.

Instead of having one word for each amino acid, you could have three words that mean the same thing.

The best way to insure the body has enough amino acid material to make the globulins is to eat foods high in globulin proteins.