7A60.XX DNA Optical Transform Kit


X-ray diffraction, DNA structure


This kit demonstrates the X-ray diffraction of DNA by using patterns scaled up to diffract using laser pointers. The slide has 12 patterns to contrast between changing amplitude, period, and offset of the sugar-phosphate backbone shapes, as well as seeing only the effect of the base pairs or phosphate groups.



  • [1] DNA optical transform kit
  • [1] Green laser pointer

Important Notes

  • Lasers can cause blindness. Use with caution.


  1. Shine the laser through various patterns as you discuss them.
  2. Slides A, B, and C show that diffraction off of lines gives an array of dots perpendicular to the lines.
  3. Slides D → G and E → H show that the X structure in the DNA diffraction pattern is caused by the helical structure of the sugar-phosphate backbone. The angle the X makes relates to the helix radius.
  4. Slides D → E and G → H show that changing the periodicity of the helix changes the spacing of the horizontal layer lines.
  5. Slides H → I show how having a double helix can make layer lines disappear.
  6. Slides F → I → L show how changing the offset between the two helices makes different layer lines disappear. L has the proper DNA helix offset.
  7. Slide K shows the diffraction pattern of the phosphate groups alone.
  8. Slide J shows the diffraction pattern of the base pairs alone.


Additional Resources



  • Don't attempt this at home!

Last revised

  • 2020


  • Original construction: purchased from the Institute for Chemical Education.

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If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.