All 20 types of amino acids contain the same basic structure and differ only in their R-group. Amino acids are encoded by RNA and are the basic building blocks of proteins.
The skeletal structure of an amino acid is always the same and contains an alpha carbon attached to an amino-group and a carboxyl-group. The R-group, referred to as the side chain, is attached to the alpha carbon and defines the amino acid. Amino acids can be divided into three groups: non-polar, polar uncharged and polar charged. The polar charged group can be further divided into acidic positively charged or basic negatively charged.