So a single DNA molecule consists of two individual nucleic acid chains that wind about a common axis and these two polynucleotide chains run in opposite directions. So although they are parallel, they run in opposite directions. B, the backbone of. So if we examine the following diagram, these are the backbones and these are the nitrogenous bases. And remember, in our study on the backbone we said that a backbone consists of these repeating units of sugar phosphate groups. So we have sugar phosphate, sugar phosphate, sugar phosphate, and that runs along the entire backbone.