Amino acids can act as acids and bases

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An amino acid contains an amino group (-NH2) as well as a carboxyl group (-COOH). The carboxyl group is acidic (proton donor) and amino group is basic (proton acceptor). Therefore amino acids are amphoteric in nature. (Amphoteric compounds are those compounds which can act both as an acid or a base). 
  • At low pH the carboxyl group accepts a proton and becomes uncharged so the overall charge on the molecule is positive. 
  • At high pH the amino group loses its proton and becomes uncharged so the overall charge on molecule is negative.
  • The pH at which the molecule carries no electrical charge is called the isoelectric point. At this point the amino acids exist as a dipolar ion or Zwitterion. A Zwitterion is a molecule with no electrical charge because it contains equal number of both positively and negatively charged ions.
                       Low pH                                                                                                           High pH


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