Which amino acid is not commonly found in an alpha helix?

Correct Answer: (C) Proline

Explanation:

• Proline: It is called a "helix breaker" because its rigid cyclic structure disrupts the hydrogen bonding and flexibility required for alpha-helix formation.
• Glutamine: Frequently found in alpha helices due to its side chain's ability to form hydrogen bonds.
• Arginine: Found in helices, as its positively charged side chain interacts with other residues.
• Tryptophan: Can stabilize helices due to its bulky, aromatic side chain that participates in hydrophobic interactions.