Final answer:
B-DNA has 10.5 base pairs per turn and is most stable under physiological conditions. Z-DNA has 12 base pairs per turn and is doubtful to exist in physiological states. The helical structures differ in spatial relationships and grooves, influencing protein interactions.
Step-by-step explanation:
Common B-DNA has 10.5 base pairs (bp) per turn with each turn of the helix spanning approximately 3.6 nm. This form of DNA is the most stable under physiological conditions. On the other hand, Z-DNA, which has a more zigzagged shape and is a less common form of DNA, characteristically has 12 base pairs per turn and the distance between each turn is 3.8 nm. However, its existence in a physiological state is doubtful. In DNA structure, the spatial relationship between the two strands creates major and minor grooves, which are important for protein interactions.
In contrast to B-DNA, Z-DNA is left-handed and its unusual structure is characterized by a more elongated and slim helix. While B-DNA's right-handed helix is the biological norm, Z-DNA could potentially play a role in certain biological processes, although it is not well understood.