This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
None Not seen in alpha helix ? 
Select and explain. 
A. Alanine, B. Leucine, C. Proline, D. Isoleucine
C: Proline
Answer: C: Proline 
Explanation: Ans. is 'c' i.e., Proline Proline is never found in a-helix as it has imino group (-NH) not amino (-N112).Thus it cannot provide hydrogen for hydrogen bonding, the major stabilizing force of a-helix.Glycine also tends to disrupt a-helix; because of its high flexibility and small size it often induces bends in a-helix.