Bubble Gum Mystery

Name:

Period:

The Scenario:

Last week your teacher found a big wad of gum on her chair. Who put the gum on the chair?
She has three very adamant gum chewers in his class. Having asked them numerous times to spit out their gum, she suspects that the gum belonged to one of them. But how can we tell whose gum it is? You can help figure out this mystery.

Some questions to get you thinking about today's lab:

What is DNA and what does it do?

What are some characteristics or properties of DNA?

How can we take advantage of these properties to help us figure out whose gum was on the chair?

What tricks can we use to see DNA?

Materials

• DNA from three suspects labeled 1, 2, 3, and the GUM (G)
• agarose
• Tris-acetate/EDTA solution (TAE)
• micropipette/tips
• electrophoresis apparatus

Procedure:

1. Get your electrophoresis apparatus. Make sure the comb is placed closest to the black electrode and that there are stoppers at both ends of the gel space.

2. Pour hot agarose into the gel space until it reaches the top of the gel box. Let the agarose harden, which should take about 10 minutes. Don't touch/move your gel until it's hard. Why not?
   
   Draw a picture of your gel and label which samples will be added to which wells before you add DNA.
   
   
   
   
   
   
   
   
   
   
   
   

3. Load your DNA SAMPLES into the wells near the BLACK ELECTRODE. Why near the black electrode? Be sure to keep track of which samples you loaded in which lanes.

4. Now pour TAE solution over your gel CAREFULLY so that is it completely covered plus a little more. What do you think the TAE solution is for?
   

5. Run that gel!! Plug the electrodes into your gel box (red to red, black to black), being careful not to bump your gel too much. Plug the power source into an outlet and set to 100 V. How can you tell your gel is running? If time permits, you will run the gel for about 30 minutes.
   
   
   

Analyzing Your DNA Data

Plug in your gel electrophoresis tray, and after 3 minutes draw another picture.










After 15 minutes draw another picture.











Once the purple dye has migrated approximately 2/3 of the gel, turn off the power and carefully remove the gel. The gel is very fragile, take care to not break it. You can remove the tray that you poured agarose on to and gently slide the gel into the staining tray. At this point you cannot see the DNA, what can you see and how do the four different lanes compare?

Once you have placed your gel into the staining tray bring it to the staining station. Completely cover the gel with methylene blue and cover try with saran wrap. Stain overnight.

Next day--Viewing the gel: Pour the methylene blue back into the bottle and carefully place the gel onto a white light box. The gel is very fragile so take care to not break it. Draw a picture of your stained gel, be as accurate as possible in drawing the bands:

What can your data tell you about who put their gum on the teacher's chair? Wouldn't be better to put the gum on the bedpost overnight...???

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BIOTECH Project Department of Molecular and Cellular Biology The University of Arizona September 18, 2000 Nadja Anderson, PhD Last Modified March 1, 2002 http://biotech.biology.arizona.edu