There are over 100 amino acids that have been found to occur naturally; each of them differs in R group. Twenty of them are involved in making up a protein, and are classified as whether they are non-essential or essential. Non-essential or dispensable amino acids are synthesized in the body. They are alanine, arginine, aspartic acid, asparagine, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine. Essential or indispensable amino acids cannot be synthesized in the body and can only be obtained through food. They are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.