1.1.2 The structure of dna Table l1 features of different conformations of the dna double helix Feature B-DNA A-DNA Z-DNA Type of helⅸx Right-handed Right-handed Left-handed Helical diameter (nm) 2.37 2.55 1.84 Rise per base pair(nm) 0.34 0.29 Distance per complete turn(pitch)(nm) 3.4 3.2 4.5 Number of base pairs per complete turn Topology of major groove Wide, deep Narrow, deep Topology of minor groove Narrow, shallow Broad shallo Narrow. de1.1.2 The structure of DNA