X-ray diffraction "photo 51"
shows a 3.4 angstrom periodicity, suggesting a helical structure of DNA B form.
- "X" pattern characteristic of helix.
- Diamonds indicate long molecules.
- Smears show distance between repeating units.
- Missing smears suggest interference from second helix.
This photo was taken by Rosalind Franklin in May 1952, and required 100 hours of exposure.
Reference:
www.pbs.org/wgbh/nova/photo51/anat-flash.html