Question

Amino acids are amphoteric in nature. This means that
A.They behaves as a base in acidic medium and as an acid in alkaline medium
B.They behaves as an acid in acidic medium and as a base in alkaline medium
C.They behaves as an acid in acidic medium or alkaline medium
D.They behaves as a base in acidic medium or alkaline medium

Answer 1

Amino acids can also act as zwitterions. There are various amino acids, out of which only 20 take part in the synthesis of proteins.

Complete answer: Amino acids are the compounds that have a minimum one -$NH_2$group and one -$COOH$group and show both acidic and basic properties. Amino acids join together to form proteins. Nearly 200-300 amino acids occur in nature, but there are only 20 amino acids that form the normal components of proteins while the rest of the amino acids do not participate in protein formation and are called Non-protein amino acids or non-standard amino acids.
Since amino acids have at least one -$NH_2$group and one -$COOH$group. They are amphoteric in nature i.e., show both acidic and basic properties. A free amino group is basic and a free carboxyl group is acidic.
Amino acids of proteins can rotate the plane of polarized light towards the left whereas non-protein amino acids rotate it either left or right side due to the presence of chiral carbon atoms. Amino acids are crystalline, organic compounds soluble in water. They can act as a Zwitterion- can carry both positive and negative charges simultaneously.
So, the correct answer is option A. They behave as a base in an acidic medium and as an acid in an alkaline medium.

Note: All the proteins except glycine possess asymmetrical alpha-carbon which makes them optically active or chiral. Glycine is the simplest amino acid having hydrogen at the R-group position.
Proline and hydroxyproline have an imine group, so are called imino acids.