amino acid

noun Biochemistry.
any of a class of organic compounds that contains at least one amino group, –NH 2 , and one carboxyl group, –COOH: the alpha-amino acids, RCH(NH 2 )COOH, are the building blocks from which proteins are constructed.


Origin:
1895–1900

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World English Dictionary
amino acid
 
n
any of a group of organic compounds containing one or more amino groups, -NH2, and one or more carboxyl groups, -COOH. The alpha-amino acids RCH(NH2)COOH (where R is either hydrogen or an organic group) are the component molecules of proteins; some can be synthesized in the body (nonessential amino acids) and others cannot and are thus essential components of the diet (essential amino acids)

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American Heritage
Medical Dictionary

amino acid n.
Abbr. AA
Any of various organic acids containing both an amino group and a carboxyl group, especially any of the 20 or more compounds that link together to form proteins.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
amino acid  
Any of a large number of compounds found in living cells that contain carbon, oxygen, hydrogen, and nitrogen, and join together to form proteins. Amino acids contain a basic amino group (NH2) and an acidic carboxyl group (COOH), both attached to the same carbon atom. Since the carboxyl group has a proton available for binding with the electrons of another atom, and the amino group has electrons available for binding with a proton from another atom, the amino acid behaves as an acid and a base simultaneously. Twenty of the naturally occurring amino acids are the building blocks of proteins, which they form by being connected to each other in chains. Eight of those twenty, called essential amino acids, cannot be synthesized in the cells of humans and must be consumed as part of the diet. The remaining twelve are nonessential amino acids.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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American Heritage
Cultural Dictionary
amino acids [(uh-mee-noh)]

Basic organic molecules that combine to form proteins. Amino acids are made up of hydrogen, carbon, oxygen, and nitrogen. Some examples of amino acids are lysine, phenylalanine, and tryptophan.

Note: Amino acids are the basic molecular building blocks of proteins.
The American Heritage® New Dictionary of Cultural Literacy, Third Edition
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Published by Houghton Mifflin Company. All rights reserved.
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Example sentences
Because amino acids have a slight electrical charge, they are pulled through
  the tube.
Proteins are made up of amino acids, some that are attracted to water, others
  that are repelled by water.
They re-supply the body with carbohydrates, usually antioxidants and sometimes
  amino acids and caffeine.
Amino acids are the key building blocks of proteins.
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