Q29 - Structure of DNA and RNA

The correct answer is C) X-ray crystallography.

Franklin fired X-rays at DNA fibres and recorded the diffraction pattern. Her famous “Photo 51” (1952) showed an X-shaped pattern typical of a helix. Watson and Crick used it to build their double-helix model.

A) Incorrect: Electrophoresis separates DNA fragments by size. It does not reveal the molecule’s structure.

B) Incorrect: Electron microscopy was not the technique Franklin used, and at the time it could not resolve the helix.

C) Correct: Franklin used X-ray diffraction, the basis of X-ray crystallography.

D) Incorrect: Chromatography separates mixtures. Chargaff used it to show A = T and G = C, but it gives no image of DNA.

E) Incorrect: MRI is a medical imaging technique developed in the 1970s.