Stability of α-Helix structure of proteins depends upon

Solution

Chemistry ma’am · 4 steps

In an α-helix, each C=O hydrogen-bonds to the N–H four residues ahead; those bonds hold the coil tight.

1. What the helix is. The α-helix is a secondary structure. The polypeptide backbone coils into a right-handed spiral, with about 3.6 amino acid residues per turn.
2. What holds it. The C=O of each peptide bond forms a hydrogen bond with the N-H of the residue four places further along the same chain. These bonds run roughly parallel to the helix axis and lock each turn to the next.
3. Why not the others. van der Waals forces and dipolar interactions are present but weak and non-specific, so they cannot fix a regular repeating shape. π-stacking needs aromatic rings, and the backbone has none.
4. So. The stability of the α-helix comes from intramolecular hydrogen bonding, which is option (b).

The idea to keep. Secondary structures (α-helix and β-pleated sheet) are held by hydrogen bonds between backbone C=O and N-H groups. In the helix they lie within one chain; in the sheet they lie between chains.

Answer from the NTA final answer key. Solution by PrepWiser.