Final answer:
The DNA double helix is right-handed, as proposed by Watson and Crick. Its structure resembles a spiral staircase with the steps being the nitrogenous bases.
Step-by-step explanation:
The conventional "handedness" of the spiral in the DNA double helix is right-handed. This means that if you were to follow the curve of the helix with your right hand, your fingers would curl in the direction of the helical twist, and your thumb would point along the axis of the helix. Watson and Crick proposed that DNA is composed of two strands forming a right-handed helix, with the sugar and phosphate groups creating the backbone on the outside, while the nitrogenous bases are paired in the interior. The structure of DNA is often compared to a spiral staircase, with the steps representing the paired bases.