The structure of hereditary material
By the middle of the twentieth century, evidence connected DNA with heredity, raising questions about how its structure stored and transmitted information. On 25 April 1953, Nature published James Watson and Francis Crick’s double-helix model alongside experimental studies. Rosalind Franklin and Raymond Gosling reported diffraction observations from DNA fibers. The proposed structure and related experimental work appeared together in the same issue.
Diffraction constrained the model
X-rays passing through oriented DNA fibers produce diffraction patterns related to molecular structure. Franklin and Gosling studied samples under different hydration conditions and examined their configurations and dimensions. Watson and Crick combined chemical constraints, molecular distances and experimental evidence in their model. Sugar and phosphate groups form the outer backbones, with bases inside and two chains arranged around a common axis.
Complementary pairing suggested copying
The model pairs adenine with thymine and guanine with cytosine. The sequence of one strand therefore determines its complement. This arrangement suggested a copying mechanism: separated strands could each guide the formation of a new partner. Storage and replication acquired a concrete molecular explanation, giving researchers questions about pairing, strand separation and synthesis that could be investigated experimentally.
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Replication was tested experimentally
In 1958, Matthew Meselson and Franklin Stahl labeled DNA in Escherichia coli with nitrogen isotopes and examined replicated molecules using density-gradient centrifugation. Their results supported semiconservative replication, in which each new molecule retains one parental strand. The structural model of 1953 thus connected with experiments on cellular processes, becoming a working foundation for understanding the copying of hereditary material.