Amino acid are organic compounds made up of carbon, hydrogen, oxygen and nitrogen. They consist of an amino group and an acidic group attached to the the same carbon called α-carbon. Thus, they are also known as α-amino acids. They are substituted methanes. Four groups occupy the four valency positions. The four groups being an amino group, a hydrogen, A carboxylic group and a variable R group. The R group could be a hydrogen(the amino acid is called glycine), a methyl group (alanine) etc. There are 20 amino acids that occur in proteins.