The 20 Standard Amino Acids

The standard 20 amino acids only differ in the structure of the side-chain or 'R' group. They can be subdivided into smaller groupings in the properties of their side-chains on the basis of similarities. They display different physicochemical properties based on the nature of their side-chain.  Some are acidic, others are basic.  Some have small side-chains, others big, bulky side-chains. Some have aromatic side-chains, others have polar. Some confer conformational inflexible, others may participate either in hydrogen bonding or covalent bonding. Some are reactive chemically.