What Did Franklin’s Data Show About the 3 Dimensional Structure of DNA?


Scott Campbell

What Did Franklin’s Data Show About the 3 Dimensional Structure of DNA?

When it comes to the discovery of the structure of DNA, most people often credit James Watson and Francis Crick. However, it is important to acknowledge the significant contributions made by Rosalind Franklin. Franklin’s research and X-ray diffraction data were critical in unraveling the mystery of DNA’s three-dimensional structure.

Rosalind Franklin’s Role

Rosalind Franklin was a brilliant scientist who specialized in X-ray crystallography, a technique used to determine the arrangement of atoms within a crystal. In the early 1950s, she was working at King’s College London when she started studying DNA fibers using this method.

Franklin’s work involved bombarding DNA fibers with X-rays and analyzing the patterns that resulted from their interaction with the crystal lattice. By carefully interpreting these patterns, she could gather valuable information about the structure of DNA.

The X-Ray Diffraction Data

Franklin’s X-ray diffraction images provided crucial insights into DNA’s structure. One of her most famous images, known as Photograph 51, revealed a distinctive pattern that hinted at a helical structure.

Photograph 51

Photograph 51 – Rosalind Franklin’s famous X-ray diffraction image (Source: Public Domain)

The photograph showed a clear cross-shaped pattern, indicating that the molecule had a regular repeating pattern. This suggested that DNA had a helical shape rather than being a random tangle of atoms.

The B Form Conformation

Based on Franklin’s data, scientists were able to deduce that DNA exists in what is known as the B form conformation. This conformation is a right-handed double helix, where two strands are wound around each other in a spiral manner.

The B form conformation has several key features:

  • Base Pairing: Franklin’s data indicated that DNA bases form specific pairs. Adenine always pairs with thymine (A-T), and guanine always pairs with cytosine (G-C).
  • Anti-Parallel Strands: The two strands of DNA run in opposite directions, with one strand oriented in the 5′ to 3′ direction and the other in the 3′ to 5′ direction.
  • Sugar-Phosphate Backbone: The backbone of the DNA molecule is made up of sugar and phosphate molecules, forming a sturdy support structure for the base pairs.

This information was instrumental in helping Watson and Crick develop their famous model of DNA’s structure, which won them the Nobel Prize in Physiology or Medicine in 1962.


Rosalind Franklin’s X-ray diffraction data played a pivotal role in uncovering the three-dimensional structure of DNA. Her work provided crucial evidence for the helical nature of DNA and its base pairing rules. Without her contributions, our understanding of genetics and molecular biology would not be as advanced as it is today.

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