def backbone(self):
        """Returns a new `Polymer` containing only the backbone atoms.

        Notes
        -----
        Metadata is not currently preserved from the parent object.
        Sequence data is retained, but only the main chain atoms are retained.

        Returns
        -------
        bb_poly : Polypeptide
            Polymer containing only the backbone atoms of the original
            Polymer.
        """
        bb_poly = Polypeptide([x.backbone for x in self._monomers], self.id)
        return bb_poly
Returns a new `Polymer` containing only the backbone atoms.

        Notes
        -----
        Metadata is not currently preserved from the parent object.
        Sequence data is retained, but only the main chain atoms are retained.

        Returns
        -------
        bb_poly : Polypeptide
            Polymer containing only the backbone atoms of the original
            Polymer.