Question on Amino Acids

What is isoelectric point for an amino acid?

Answer:

Amino Acids exists in the dipolar ionic form known as the “Zwitter” ions. This dipolar ionic form can behave as a base as well as an acid.

In the above reaction scheme (B) is the dipolar ion, (A) is the conjugate acid of the dipolar ion and (B) is the conjugate base of the dipolar ion. In an solution of amino acids all the three forms will be existing.

It is evident that as the solution becomes basic the equilibrium will shift forward and as the solution becomes acidic the equilibrium will shift backward. So, depending on the pH of the solution there will be either an excess concentration of (A) or (B). There will be a particular pH at which the concentrations of both (A) and (B) are equal. That pH is called the isoelectric point for an amino acid.