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