Question

Which bonds in the backbone of a peptide can rotate freely?

Short answer

The partial double-bond character prevents free rotation about the peptide bond, so the carbon and nitrogen atoms of the peptide bond and the two atoms to which each is attached are held rigidly in a plane. This regional planarity affects the way a chain of amino acids can fold.

Step-by-step solution

Step-by-step-solutionStep 1: Rotation around peptide bond

The partial double-bond character prevents free rotation about the peptide bond, so the carbon and nitrogen atoms of the peptide bond and the two atoms to which each is attached are held rigidly in a plane. This regional planarity affects the way a chain of amino acids can fold.

Backbone of a peptide

The alpha carbon (α-carbon or Cα) is what connects the amino group to the acid carboxyl group. The bonds on either side of the $\mathrm{\alpha }$-carbon in the backbone of a peptide can freely rotate.

Backbone of a peptide