This amino acid residue disrupts the or helix because its si

This amino acid residue disrupts the or helix because its side chain contains a unique ring structure that restricts bond rotations, Pro Phi Tarp His

Solution

ANSWER : The correct answer is A (Pro/Proline)

Explanation : In proline, the nitrogen atom is part of a rigid ring and rotation about the N-C alpha bond is not possible. Thus, a Proline residue introduces a destabilizing kink in an alpha helix. In addition, the nitrogen atom of a Proline residue in peptide linkage has no substituent hydrogen to participate in hydrogen bonds with other residues. For these reasons, proline is only rarely found within an alpha helix.