def rise_per_residue(self):
        """The rise per residue at each point on the Primitive.

        Notes
        -----
        Each element of the returned list is the rise per residue,
        at a point on the Primitive. Element i is the distance
        between primitive[i] and primitive[i + 1]. The final value
        is None.
        """
        rprs = [distance(self[i]['CA'], self[i + 1]['CA'])
                for i in range(len(self) - 1)]
        rprs.append(None)
        return rprs