These two effects can be linked to the distinct helical conformations of B-DNA and A-RNA helices, as the orientation of the phosphate groups strongly differs between the two double helical conformations (Figure ). The phosphate group points away from the helix principal axis in B-DNA, whereas it is more parallel to the axis in A-RNA (see α OP 2 angle in Figure and). This results in different orientations of the phosphate oxygen atoms: