What Is True About the Rotation About Bonds in a Protein

Multiple Choice

What is true about the rotation about bonds in a protein backbone?

A) The rotation is free about all bonds in the backbone,except for the bond between the nitrogen and the alpha carbon in proline residues.
B) The bond between the carbonyl carbon and nitrogen is restricted.Other bonds are free to rotate depending only on steric hindrance or the presence of proline residues.
C) All bonds in the backbone have restricted rotation and partial double-bond character.
D) The rotation is free only about the peptide bond.The other bonds are restricted by steric hindrance and the presence of proline residues.