Final answer:
The DNA component analogous to the spiral staircase's banister is the sugar-phosphate backbone, which forms the structural framework on the outside of the DNA double helix.
Step-by-step explanation:
The component of DNA that is analogous to the banister (side rails) of a spiral staircase is the sugar-phosphate backbone. In the double helix structure of DNA, this backbone forms the structural framework on the outside of the helix, just as the banisters run along the sides of a staircase. The banisters support the structure of the staircase and, similarly, the sugar-phosphate backbone provides support and protection for the DNA molecule.
The strands of DNA are connected by pairs of nitrogenous bases, which are like the steps in the staircase. There are four nitrogenous bases in DNA: adenine (A), thymine (T), guanine (G), and cytosine (C). These bases pair specifically (A with T and G with C) to form the steps that support the twist of the double helix.