amino acid 1

Structure of amino acids
The natural amino acid s are mainly ?-amino acids, All except glycine contain asymmetric or chiral carbon atom. It is a carbon atom that is attached to four different chemical groups (four different substituted groups)
There are 20 amino acids commonly found in proteins and these differ from each other in the nature of the R-groups attached to the alpha carbon.
Amino acid has an optical activity in solution and can be present in two isomers; The (dextrarotatory) (+) isomer which has the ability to rotate the plane of polarized light to the right.
The (laevorotatory) (-) isomer which has the ability to rotate the plane of polarized light to the left.
So both isomers can rotate the plane of polarized light by the same magnitude but in opposite directions.
•Amphoteric properties of amino acids: that is they have both basic and acidic groups and so can act as base or acid.
• Neutral amino acids (monobasic, monocarboxylic) exist in aqueous solution as “ Zwitter ion” i.e. contain both positive and negative charge. Zwitter ion is electrically neutral and can’t migrate into electric field.
• The isoelectric point (IEP) of an amino acid is the pH at which the amino acid has a neutral charge (i.e. is the pH at which the zwitter ion is
formed. e.g IEP of alanine is 6)

At physiological pH (7.4), -COOH group is dissociated forming a negatively charged carboxylate ion (COO-) and amino group is protonated forming positively charged ion (NH3+) forming Zwitter ion.