In a Ramachandran Diagram the Region Representing the Angles Of \phi

Multiple Choice

In a Ramachandran diagram the region representing the angles of $\phi$ and $\varPsi$ that correspond to those commonly made by an amino acid that favors a left-handed $\alpha$ helix are different from those angles commonly made by an amino acid that favors right-handed $\alpha$ helix formation.Which of the following statements provides a plausible explanation for this difference?

A) Groups which would normally undergo high steric hindrance in the right-handed arrangement are separated maximally in the left-handed arrangement.
B) Left-handed helices have smaller pitch than right-handed helices.
C) The peptide backbone can coil tighter in the left-handed helices than in the right-handed helices.
D) Left-handed helices exhibit cyclic symmetry,while righthanded helices are asymmetric.
E) All of the above are plausible explanations.