Concepts

X-ray diffraction, DNA structure

Overview

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.

Details

Equipment

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

Important Notes

• Lasers can cause blindness. Use with caution.
• The associated booklet contains background information on DNA structure.
  

Script

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