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How did James Watson and Francis Crick determine the double-helix structure of DNA?

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Diagram of a DNA double helix showing its twisted ladder structure, with a close-up of the sugar-phosphate backbone, paired nitrogenous bases (adenine, thymine, cytosine, guanine), and labeled nucleotides and hydrogen bonds. — human genome The human genome is made up of approximately three billion base pairs of deoxyribonucleic acid (DNA). The bases of DNA are adenine (A), thymine (T), guanine (G), and cytosine (C).

In 1953, James Watson and Francis Crick determined the double-helix structure of DNA by constructing a molecular model that accounted for known physical and chemical properties of the molecule.12

Their breakthrough relied heavily on X-ray diffraction data produced by Rosalind Franklin and Maurice Wilkins, which provided evidence of the helical structure. Additionally, they utilized biochemist Erwin Chargaff’s findings, which indicated that the amount of adenine always equals thymine and guanine always equals cytosine.123

By creating a wire model, Watson and Crick demonstrated that these base pairs formed a "lock-and-key" fit, allowing the molecule to form a stable, twisted ladder shape. Their model revealed that the two strands are antiparallel and held together by hydrogen bonds. This structure elegantly explained how DNA could serve as a hereditary molecule, as the strands could separate to act as templates for self-replication. It is important to acknowledge that Franklin’s critical contributions, including her X-ray images, were used as evidence in this discovery without her permission.1234