Final answer:
DNA's double helix structure is due to bonds between sugar and phosphate groups forming two strands with interior nitrogenous bases paired and held together by hydrogen bonds, resembling a spiral staircase.
Step-by-step explanation:
The Double Helix Structure of DNA
The famous double helix structure of DNA, resembling a spiral staircase, comes from the way its components interact with each other. The structure consists of two strands formed by bonds between phosphate and sugar groups of nucleotides. The rungs of the staircase are comprised of nitrogenous base pairs; adenine pairs with thymine and guanine pairs with cytosine. These base pairs are bonded together by hydrogen bonds. The entire structure coils around itself due to the nature of these interactions, making the double-stranded DNA very stable and difficult to break apart. James Watson and Francis Crick, building on the X-ray crystallography work of Rosalind Franklin and others, proposed this double helix model.
The sugar-phosphate backbone serves as the outer structure of the DNA double helix, while the base pairs form the interior, connected by hydrogen bonds every 0.34 nm. This assembly allows DNA to maintain its shape, necessary for replication and numerous nucleic acid interactions. The strands are antiparallel, highlighting their opposite orientations important for biological functions.