In chemistry, an amino acid is a molecule that contains both amine and carboxyl functional groups. In biochemistry, this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent.[1] In the alpha amino acids, the amino and carboxylate groups are attached to the same carbon, which is called the ?-carbon. . Amino acids combine in a condensation reaction that releases water and the new 'amino acid residue' that is held together by a peptide bond. Proteins are defined by their unique sequence of amino acid residues; this sequence is the primary structure of the protein. Twenty standard amino acids are used by cells in protein biosynthesis, and these are specified by the general genetic code. These 20 amino acids are biosynthesized from other molecules, but organisms differ in which ones they can synthesize and which ones must be provided in their diet. The ones that cannot be synthesized by an organism are called essential amino acidschemical industries as well as agriculture and environmental engineering