2. The α-helix in proteins is formed due to
a. Intramolecular hydrogen bonds
b. Intermolecular hydrogen bonds
c. van der Waals interactions between amino acids
d. Ionic interactions

α-Helix Formation in Proteins: Intramolecular Hydrogen Bonds Explained

The correct answer is a. Intramolecular hydrogen bonds. These bonds stabilize the α-helix by linking the carbonyl oxygen (C=O) of one amino acid to the amide hydrogen (N-H) of the amino acid four residues ahead within the same polypeptide chain.​

Option Analysis

• a. Intramolecular hydrogen bonds: Correct. In the right-handed α-helix, hydrogen bonds form intra-chain between the backbone N-H of residue i and C=O of residue i-4, creating 3.6 residues per turn and stabilizing the coil.​

• b. Intermolecular hydrogen bonds: Incorrect. These occur between separate polypeptide chains, as in β-sheets, not within a single chain of the α-helix.​

• c. van der Waals interactions between amino acids: Incorrect. While van der Waals forces contribute to side-chain packing, they do not primarily form or stabilize the α-helix backbone.​

• d. Ionic interactions: Incorrect. Salt bridges from charged side chains may support helices secondarily, but the core structure relies on hydrogen bonds, not ionic forces.​

The α-helix in proteins is formed by intramolecular hydrogen bonds, a key concept for CSIR NET Life Sciences aspirants studying protein secondary structure. This right-handed coil features hydrogen bonds between the N-H group of one amino acid and the C=O group four residues earlier, ensuring structural rigidity with 3.6 residues per turn.​

Structural Features

Hydrogen bonds align parallel to the helix axis, while side chains project outward, avoiding steric clashes. Proline disrupts helices due to its rigid ring, whereas alanine favors formation.​

Comparison with β-Sheet