Amino Acids are a class of more than 20 naturally occuring hydrocarbon molecules containing an amine group, a carboxylic acid group and a side chain that varies between different amino acids. These molecules are particularly important in biochemistry. Amino acids combine to form proteins in living things. The so called 'normal' amino acids include: alanine, aspartic acids (also called asparagine), cysteine, glutamic acid (also called glutamine), phenylalanine, glycine, histidine, isoleucine, lysine, leucine, methionine, proline, arginine, serine, threonine, valine, tryptophan and tyrosine. Other amino acids have been synthesized and are used in medicine. They are incorporated into proteins by transfer RNA according to the genetic code.