Amino acids are organic compounds that are the building blocks from which proteins are made. They are common to all living things, but they are not a part of lipids or carbohydrates, and they are not found in inorganic materials such as minerals, water, air and metal.
Amino acids are made up of at least one amino group and one carboxyl group. While there are about 500 known amino acids, only 23 are used for protein building. All of the vast assortment of proteins present in the life forms found on earth are made up of those 23 amino acids. In humans, many non-protein amino acids serve other functions in the body, generally as precursors to neurotransmitters and other types of metabolic intermediates.