What is the shape of the DNA molecule described by Watson and Crick?

Watson and Crick described DNA as a double helix: two complementary strands twisted around a common axis. The shape is often compared with a twisted ladder, with the sugar-phosphate backbones forming the sides and paired bases forming the rungs, but the canonical scientific answer is double helix.

The model, published in 1953, explained how DNA could both store biological information and be copied. Bases pair specifically: adenine with thymine, and guanine with cytosine. Because each strand carries complementary information, the strands can separate and serve as templates during replication.

The discovery depended on evidence from several researchers. Rosalind Franklin and Raymond Gosling produced important X-ray diffraction data, including Photo 51, while Maurice Wilkins contributed additional experimental evidence. Erwin Chargaff’s base-composition findings also helped constrain the model. DNA is not generally a single or triple helix in cells. The familiar cellular form is B-DNA, a right-handed double helix with roughly 10 base pairs per turn, although other helical forms can occur under different conditions.