Final answer:
The spiral in the DNA double helix is conventionally right-handed, consisting of two antiparallel strands formed by nucleotides with a sugar-phosphate backbone.
Step-by-step explanation:
The conventional direction of the spiral in the DNA double helix is right-handed. DNA is composed of two helical chains that coil around the same axis, forming this right-handed double helix. These two strands of DNA consist of nucleotides, with the sugar and phosphate molecules forming the exterior 'backbone' of the helix and the nitrogenous bases, A (adenine) pairing with T (thymine) and C (cytosine) pairing with G (guanine), located on the inside. Each strand runs anti-parallel to the other; this means that the 5' end of one strand is aligned with the 3' end of the opposing strand.
Furthermore, Watson and Crick's discovery underscores the antiparallel nature of the two DNA strands, a crucial aspect for the function and replication of DNA. The antiparallel orientation and right-handed coiling facilitate accurate DNA replication and the vital genetic information is carried in the sequence of these nitrogenous bases, which are often compared to the steps of a spiral staircase.