RNA or DNA sequences may be prefixed with r or d if not understood from context. Features of the Model for B-form DNA Two strands. Strands are antiparallel. Helix rise per base pair is 0.34 nanometers. Ten base pairs per helical turn.
Phosphates are on the outside of the molecule.
Base pairs are in the inside of the molecule stacked close to each other. Inside cells, B-DNA has an average of 10.5 base pairs per helical turn. Some of the parameters describing these structures are summarized in Table 4.3 . Pyrimidines usually cannot adopt the syn -conformation. The conversion of double helical DNA into single strands is called denaturation.