Suppose you have a 20-residue polypeptide in an alpha-helical conformation and a 20 base pair double-helical piece of DNA. Compare the two structures in terms of
(a) the units that repeat in the backbone of the polymer chain
(b) the projection in space of substituents along the backbone (R-groups in the polypeptide and bases in the DNA) relative to the axis of the helix
(c) the type of covalent bond joining the monomers