Amino acids are composed primarily of carbon, hydrogen, oxygen and nitrogen. These acids form amine and carboxylic acid functional groups and a side-chain unique to each amino acid.
Amino acids are building blocks of proteins. Initially discovered in the 19th century, the majority of our current knowledge of amino acids was discovered in 1902, with the proposition that amino acid chains, joined at the carboxyl groups, result in the formation of proteins. These linear chains were named peptides, a term still used today.
The most common amino acids found in nature are alpha amino acids. Each amino acid features a carbon atom adjacent to the carboxyl group, which is referred to as the α–carbon. Alpha amino acids are characterized by an amino group directly bonded to the α–carbon. Amino acids are typically broken up into four groups: weak acid, weak base, hydrophile or hydrophobe. The group an amino acid belongs to is determined by the structure of its side chain.
Amino acids are further classified as being canonical or non-canonical. Canonical amino acids are the 20 encoded directly in the universal genetic code. Non-canonical amino acids are primarily non-proteinogenic, meaning that they cannot form proteins. There are however, three non-canonical amino acids that are capable of creating proteins with information not in the universal genetic code.