The shape of a DNA molecule is usually referred to by a two-word phrase, one of whose words refers to its three-dimensional spiral shape. What is this phrase?

This famous two-word phrase perfectly captures the elegant structure of our genetic blueprint. The "double" part of the term refers to the two long, complementary strands that make up the molecule. The word "helix" is a geometric term for a three-dimensional spiral, describing the corkscrew-like twist that these two strands take as they wind around a central axis. This creates an iconic shape often compared to a twisted ladder, where the sides are made of sugar-phosphate backbones and the rungs consist of paired nucleotide bases.

The discovery of this structure in 1953 by scientists James Watson and Francis Crick was a landmark moment in biology. Their model was revolutionary because it immediately suggested how DNA could both store vast amounts of genetic information and be faithfully copied for new cells. Their breakthrough, however, was heavily reliant on the work of chemist Rosalind Franklin. Her groundbreaking X-ray diffraction image, known as Photo 51, provided the critical evidence that confirmed the molecule's helical nature and was essential for developing the final, correct model.