Match List-I with List-II.
| List-I (Term) | List-II (Description) |
|---|---|
| (A) Zwitter ion | (I) Reacts both with acids and with bases |
| (B) Amphoteric behaviour | (II) The specific sequence in which amino acids are linked in a polypeptide |
| (C) Peptide linkage | (III) A dipolar ion that is neutral but contains both positive and negative charges |
| (D) Primary structure of a protein | (IV) An amide formed between a –COOH group and an –NH2 group |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A-III, B-I, C-IV, D-II
The first two terms describe a single amino acid in water; the last two describe how amino acids are joined in a protein.
(A) Zwitter ion — This matches (III) A dipolar ion that is neutral but contains both positive and negative charges. In water the –COOH group loses a proton and the –NH2 group accepts one, giving \( \ce{H3N^+-CH(R)-COO^-} \).
(B) Amphoteric behaviour — This matches (I) Reacts both with acids and with bases. It is what the zwitter ion does: the –COO− end takes up H+ from an acid, and the –NH3+ end gives H+ to a base.
(C) Peptide linkage — This matches (IV) An amide formed between a –COOH group and an –NH2 group, the –CO–NH– bond formed with loss of water.
(D) Primary structure of a protein — This matches (II) The specific sequence in which amino acids are linked in a polypeptide. Any change in this sequence creates a different protein.
NCERT (2026-27 edition):
10.2.2 Classification of Amino Acids – “…In aqueous solution, the carboxyl group can lose a proton and amino group can accept a proton, giving rise to a dipolar ion known as zwitter ion. This is neutral but contains both positive and negative charges.”
“In zwitter ionic form, amino acids show amphoteric behaviour as they react both with acids and bases.”
10.2.3 Structure of Proteins – “…Chemically, peptide linkage is an amide formed between –COOH group and –NH2 group.”
“(i) Primary structure of proteins: …Each polypeptide in a protein has amino acids linked with each other in a specific sequence and it is this sequence of amino acids that is said to be the primary structure of that protein.”