Which of the following amino acids have the least and most favorable phi and psi angle on the Ramachandran plot?
Select one: a. Proline and Alanine b. Proline and Glycine c. Histidine and Glycine d. Tryptophan and Alanine
Ans.b) Proline and Glycine
Proline has restrictions in phi-psi space that arise from the 5-membered ring. Phi is restricted to approxamatly -60 by the ring and psi angles fall into two groupings near -45 and +135 in the helical and sheet regions of the Ramachandran plot.
In glycine, the ψ angle is typically clustered at ψ = 180° and ψ = 0°.
They(proline and glycine) exist at the two extreme ends of the spectrum in terms of phi/psi rotation. Gly is the least restricted, Pro is the most restricted. Thus Gly can appear anywhere & Pro only in certain places.
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