Final answer:
a) Clockwise. A and B form DNA twist in a clockwise direction, while Z-DNA twists in a counterclockwise direction.
Step-by-step explanation:
A and B form DNA twist in a clockwise direction. This is because DNA is a right-handed double helix, with the strands coiled around each other in a spiral staircase-like structure. The direction of the twist is determined by the arrangement of the sugar-phosphate backbone and the nitrogenous bases.
On the other hand, Z-DNA is a left-handed double helix, which means that it twists in a counterclockwise direction. Z-DNA forms under certain conditions, such as high salt concentrations or alternating purine-pyrimidine sequences.
In summary, A and B form DNA twist in a clockwise direction, whereas Z-DNA twists in a counterclockwise direction.