Assertion  :     $\mathrm{\alpha } -$amino acids exist as dipolar ions or zwitter ions

Reason     :     $\mathrm{\alpha } -$ amino acids are the building blocks of  proteins

In acidic medium -COOH  group acts as the base and accepts a proton. As a result, $\mathrm{\alpha }$ -amino acids exist as cations in acid  medium and migrate towards cathode under the influence of an electric field.

 In alkaline ·I medium  $N{H}_3$  group acts as the acid and thus loses a proton. As a result, a-amino acids exist as anion and migrate. towards anode under the influence of an electric field. 

However at some intermediate value of pH,  be concentration of cationic form and anionic form will become equal and hence there is no net migration of $\alpha$ - amino  acid under the influence  of an electric field.