Elementary plant Biochemistry and Biotechnology (2+1)

Amphoteric nature of amino acids

 
• Amino acids are amphoteric compounds, as they contain both acidic (COOH) and basic (NH2) groups.
• They can react with both alkalies and acids to form salts.
  
• In acid solution amino acids carry positive charges and hence they move towards cathode in an electric field.
• In alkaline solution, the amino acids carry negative charges and therefore move towards anode.When an amino acid is dissolved in water, it exists as inner salt carrying both positive and negative charges.
• This occurs as a result of dissociation of carboxyl group to release the H+ ion, which passes from the carboxyl to the amino group.
• The amino acids possessing both positive and negative charges are called zwitterions.
• The zwitterion reacts as an acid with a base by liberating a proton (H+) from the NH3+ group and as a result possesses a net negative charge.
  
• On the other hand, zwitterions reacts with an acid as base, combining with the proton (H+) of the acid resulting in the formation of a compound having a net positive charge. These reactions are reversible.
• The p^H at which the amino acid has no tendency to move either towards positive or negative electrode is called isoelectric pH or isoelectric point .
  
• At isoelectric pH, the amino acid molecule bears a net charge of zero.