Polar, Charged Amino Acids

Remaining all amino acids has polar, hydrophilic side-chains, some of which are charged at neutral pH. On the side-chains the amino groups of the basic amino acids arginine (Arg or R) and lysine (Lys or K) are protonated and therefore positively charged at neutral pH.  The side-chain of histidine (H or His) may be either positively uncharged or charged at neutral pH. on the contrary,  the carboxyl  groups  on the side-chains  of the acidic amino acids aspartic  acid (aspartate;  Asp or D) and glutamic  acid (glutamate; Glu or E) are de-protonated  and possess a negative charge at neutral  pH.