what are peptide backbones
A protein is a polypeptide, a linear polymer of many amino acids, linked by peptide bonds. The peptide linkages, along with the a-carbon atoms to which R-groups are attached, form the protein backbone, with sequence NCCNCCNCCNCC...n an a-helix, the amino acid R-groups protrude out from the helically coiled polypeptide backbone. The surface of an a-helix largely consists of the R-groups of amino acid residues. At right, an a-helix is shown end-on and from the side.