(Molecular biology) Describes the familiar structure of double-stranded DNA, which has now become an icon of pop culture. Perhaps best described as a steep spiral staircase, with the backbone of each strand of DNA (composed of repeating ribose and phosphate groups) serving as the framework of the staircase, while the individual steps are base pairs. The double helix structure of DNA was first elucidated by Watson and Crick (with more than a little help from the crystallographer Rosalind Franklin) in 1953.