Question

Define isoelectric point of amino acid. The isoelectric point of alanine is 6.1.write the molecular form of alanine at \[pH\] 5.

Answer 1

Hint: The \[pH\] at which there is no net migration of amino acid under the influence of applied electric field is called isoelectric point. \[pH\] 5 that is acidic medium and in acidic medium amino acid goes towards cathode.

Complete step by step answer: Amino acid contains both acidic and basic groups that are carboxyl group and amino group respectively. These two groups interact with each other and there is transfer of proton from carboxyl group to amino group within the molecule.as a result amino acid exists as a dipolar ion. Which is called zwitterion.

In acidic medium amino acids exist as a cation and thus migrate towards cathode under the influence of electric field. On other hand in alkaline medium amino acid exist as anion hence migrate towards anode under the influence of electric field.at some intermediate value of \[pH\]concentration of cationic and anionic form are equal and hence amino acid exist as a dipolar ion that is it contains both cation and anion (zwitter ionic form) at this \[pH\]there is no net migration of amino acid in an electric field. Therefore,That \[pH\]at which there is no net migration of amino acid under the influence of applied electric field is called isoelectric point.
Given: the isoelectric point of alanine is 6.1
So, below isoelectric point i.e. \[pH\]= 5 is the acidic medium and as we discussed above in acidic medium amino acid exists as cation.
Therefore molecular form of alanine at \[pH\]= 5 is

Note:
For neutral amino acid isoelectric point is slightly less than 7
For acidic amino acid isoelectric point is lies between 3 - 5.4
For basic amino acid isoelectric point lies between 7.6 - 10.8.
At isoelectric point amino acid has least solubility in water and hence this property has been used in the separation of different amino acids obtained from hydrolysis of protein.