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Q. phi, psi angles of a peptide segment adopting alpha helical conformation would be around

(1)-78, +59

(2) +49,+26

(3)-57,-78

(4)-60,-40

The alpha helix is characterized by backbone dihedral angles (φ and ψ) that typically fall within a narrow range. For a right-handed alpha helix, the commonly accepted values are approximately:

• φ (phi) ≈ –57° to –60°
• ψ (psi) ≈ –47° to –40°

Among the options provided:

1. (–78, +59) – The ψ angle is positive, which is not typical for an alpha helix.
2. (+49, +26) – Both angles are positive, which does not match the typical negative angles of an alpha helix.
3. (–57, –78) – While the φ angle is in the acceptable range, the ψ angle is too negative compared to the typical values.
4. (–60, –40) – Both angles fall within the expected range for an alpha helical conformation.

Thus, the correct answer is:

(4) –60, –40.