This set contains the four atoms of each amino acid that form the polypeptide N-C-C-O backbone of proteins, and the atoms the sugar phosphate backbone of nucleic acids. Use the RasMol predefined sets protein and nucleic to distinguish between the two forms of backbone. Atoms in nucleic acids and proteins are either backbone or sidechain. This set is equivalent to the RasMol expression "(protein or nucleic) and not sidechain"
The predefined set mainchain is synonymous with the set backbone.