The DNA must be stained in order to be seen. DNA can be stained with fluorescent or chemical dyes. Research laboratories use ethidium bromide, an ultraviolet (UV) fluorescent stain, because it shows very small amounts of DNA and is faster to use. Ethidium bromide, however, can cause cancer and mutate DNA. We will use methylene blue, a chemical dye, which binds to DNA. Methylene blue may stain your hands and clothes if you spill it, but it is not toxic.
Hint: Wear gloves when working with methylene blue.

1. Place the gel in a petri-dish or plastic container which is a little larger than the gel. Add enough 0.025% methylene blue solution to cover the gel about 1/4". Stain the gel for 20-30 minutes.
   
   
2. Carefully pour off as much of the methylene blue solution as possible into a small beaker. Your entire gel will appear deep blue.
   Hint: Save the methlyene blue solution; it may be reused many times.
   
   
3. Rinse the gel in running tap water. Let gel soak covered with water for 10 minutes. Rock the tray occasionally to help destain the gel. Repeat 3-4 times. The DNA bands will become more distinct as the gel destains.
   Hint: If necessary, you may continue to destain the gel overnight in a small amount of water; the gel will destain too much if left in a large amount of water. Cover the staining tray to prevent evaporation.
   
   
4. Draw the bands on your gel sketch; use rulers to ensure the proper location of the bands.
   
   
5. You may choose to photograph/photocopy your gel or view it on the overhead projector. Gels can be stored in plastic zip lock bags in the refrigerator.
   
   
   
   

Science Education Connection Department of Biochemistry The University of Arizona Tuesday, January 14, 1997 warder@u.arizona.edu http://biology.arizona.edu/sciconn/lessons/vuturo/ All contents copyright © 1997. All rights reserved.