Match List-I with List-II :
| List-I | List-II |
| (A) Amino acids linked in a specific sequence | (I) Primary structure of proteins |
| (B) Regular folding of a specific sequence of amino acids due to H-bonding | (II) Secondary structure of proteins |
| (C) Fibrous proteins | (III) Quaternary structure of proteins |
| (D) Spatial arrangement of two or more polypeptide chains | (IV) Tertiary structure of proteins |
Choose the correct answer from the options given below :
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A) - (I), (B) - (II), (C) - (IV), (D) - (III)
The structure of a protein is described at four levels, each built on the previous one: the sequence of amino acids, the regular folding of the chain by hydrogen bonds, the folding of the whole chain, and the arrangement of several chains.
(A) Amino acids linked in a specific sequence — This matches (I) Primary structure of proteins. The sequence of amino acids in each polypeptide chain is its primary structure; any change in it creates a different protein.
(B) Regular folding of a specific sequence of amino acids due to H-bonding — This matches (II) Secondary structure of proteins. Hydrogen bonds between the >C=O and –NH– groups of the peptide bonds fold the chain into the α-helix or the β-pleated sheet.
(C) Fibrous proteins — This matches (IV) Tertiary structure of proteins. The tertiary structure is the folding of the whole chain, and it gives the two main molecular shapes, fibrous and globular.
(D) Spatial arrangement of two or more polypeptide chains — This matches (III) Quaternary structure of proteins. A protein made of two or more chains (sub-units) has a quaternary structure, which is the arrangement of these sub-units with respect to each other.
Shortcut: The pair (C)–(IV) appears only in Option (3).