H-bond does not exist in :

Answer & explanation

Correct answer: option 4

The correct answer is Option (4) → Primary structure of proteins

The structure of a protein is described at four levels:

Primary structure: the sequence of amino acids in the polypeptide chain, held together by covalent peptide bonds (−CO−NH−). No hydrogen bonds are involved in defining it.
Secondary structure: the shape of the chain, the α-helix or β-pleated sheet, produced by hydrogen bonds between the >C=O and −NH− groups of the peptide bonds.
Tertiary structure: the folding of the whole chain (fibrous or globular), stabilised by hydrogen bonds, disulphide links, van der Waals and electrostatic forces.
Quaternary structure: the arrangement of two or more polypeptide subunits.

Option (1) tertiary structure of proteins — H-bonds exist in it. Hydrogen bonds are among the forces, with disulphide links, van der Waals and electrostatic forces, that hold the folded tertiary structure together.
Option (2) α-helix structure of proteins — H-bonds exist in it. The helix is held by hydrogen bonds between the −NH group of one amino acid residue and the C=O of an adjacent turn.
Option (3) β-pleated structure of proteins — H-bonds exist in it. The stretched chains lying side by side are held together by intermolecular hydrogen bonds.
Option (4) Primary structure of proteins — H-bond does not exist in it. The primary structure is only the sequence of amino acids, fixed by covalent peptide bonds; hydrogen bonds play no part in it.

NCERT (2026-27 edition):
Primary Structure of Proteins – “Proteins may have one or more polypeptide chains. 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.”

Secondary Structure of Proteins – “The secondary structure of protein refers to the shape in which a long polypeptide chain can exist. They are found to exist in two different types of structures viz. α-helix and β-pleated sheet structure. These structures arise due to the regular folding of the backbone of the polypeptide chain due to hydrogen bonding between >C=O and –NH– groups of the peptide bond.”

H-bond does not exist in :

Answer & explanation

Correct answer: option 4

The correct answer is Option (4) → Primary structure of proteins

The structure of a protein is described at four levels:

Primary structure: the sequence of amino acids in the polypeptide chain, held together by covalent peptide bonds (−CO−NH−). No hydrogen bonds are involved in defining it.
Secondary structure: the shape of the chain, the α-helix or β-pleated sheet, produced by hydrogen bonds between the >C=O and −NH− groups of the peptide bonds.
Tertiary structure: the folding of the whole chain (fibrous or globular), stabilised by hydrogen bonds, disulphide links, van der Waals and electrostatic forces.
Quaternary structure: the arrangement of two or more polypeptide subunits.

Option (1) tertiary structure of proteins — H-bonds exist in it. Hydrogen bonds are among the forces, with disulphide links, van der Waals and electrostatic forces, that hold the folded tertiary structure together.
Option (2) α-helix structure of proteins — H-bonds exist in it. The helix is held by hydrogen bonds between the −NH group of one amino acid residue and the C=O of an adjacent turn.
Option (3) β-pleated structure of proteins — H-bonds exist in it. The stretched chains lying side by side are held together by intermolecular hydrogen bonds.
Option (4) Primary structure of proteins — H-bond does not exist in it. The primary structure is only the sequence of amino acids, fixed by covalent peptide bonds; hydrogen bonds play no part in it.