Name of the scientist whose X-ray photographs of the DNA molecule provided clues needed to solve its structure?

• A. James Watson
• B. Francis Crick
• C. Rosalind Franklin
• D. Linus Pauling

Answer: (C)

X-ray diffraction data reveal the overall geometry of a molecule. Rosalind Franklin's DNA fiber diffraction images, especially the high-quality photographs she produced, showed an X-shaped pattern consistent with a helical structure. The pattern indicated a uniform diameter and a regular rise per base pair, pointing to a right-handed double helix with two sugar-phosphate backbones on the outside and paired bases inside. This concrete structural information, together with Chargaff's rules, allowed Watson and Crick to assemble the correct double-helix model. Linus Pauling proposed a different arrangement and didn't provide the diffraction evidence that resolved DNA's structure, so his model did not match the actual molecule. Thus, the scientist whose X-ray photographs provided the essential clues is Rosalind Franklin.