Rainbow Electrophoresis

Sandy Collins and Theresa Knapp
1993 Woodrow Wilson Biology Institute

This module introduces students to the principles of gel electrophoresis and also provides an opportunity for students to practice loading gels and pipetting. In this laboratory activity, food color will be separated into constituent pigments. The lab can be run with standard electrophoresis equipment or with inexpensive homemade electrophoresis equipment. (See Desktop Electrophoresis by Addie Jackson.)

TARGET AGE/ ABILITY GROUP

Grades 7-12. We recommend that students be familiar with micropipetting techniques.

STUDENT/CLASS TIME REQUIRED:

1 period (45 minutes)

MATERIALS

• electrophoresis chamber
• 1% agarose gel
• TRIS/Borate/EDTA (TBE) buffer (1X concentration)
• power source
• 4 test tubes or microcentrifuge tubes, each containing a pure food color
• 1 test tube or microcentrifuge tube containing a mixture of 4 food colors
• 5 micropipets, 1 for each test tube or microcentrifuge tube
• paper towels
• plastic sandwich bag
• student instruction handout for each student
  

TEACHER'S GUIDE FOR PREPARATION OF MATERIALS

Total preparation time: 45 minutes

We suggest that teachers prepare the gels prior to the lab. This will allow more time for discussion and avoid a step that is not critical in understanding the principles of electrophoresis. If adequate time and equipment are available, a teacher might demonstrate gel preparation.

Running gels at approximately 95 V resulted in clear separations of the pigments in the food color within 30 minutes. Green food color produces dark blue and yellow bands; red food color produces pink and red/orange bands; yellow food color produces pink, orange and yellow bands; blue food color produces light blue, dark blue, and dark red bands.

Food Color Preparation

MIx 1 drop of food color with 1 drop of water to provide enough dye solution (of that color) for 7 groups. We found that the food color solution will sink into the wells. If this is not the case with the brand you use, add 1 drop of glycerol or a few grains of table sugar to weight the food color. The multi-colored mixture can serve as a standard or unknown for the experiment.

Buffer may be flushed down the sink and gels discarded in the trash. Students may save the gels in plastic bags for later discussion, completion of analysis, or to share with parents. After 24 hours, the colors will remain vivid but the bands will no longer be discrete.

Safety

Follow all guidelines for safe use of electrophoresis equipment.

RAINBOW ELECTROPHORESIS

Adapted from an activity by Laura Cox, Glenbard South H.S.,Glen Ellyn, IL

Electophoresis is a technique used by scientists to separate compounds such as DNA and protein. When an electrical current is applied, the molecules will move through a gel. The direction and distance that the molecules migrate is related to the size and charge. In todayÌs lab, you will use electrophoresis to separate food color into its component pigments.

Materials: (per group)

• electrophoresis chamber and power source
• 5 test tubes with various food colors
• 5 pipets, one for each color (Be sure to keep
• these separate!)
• plastic sandwich bag
  

INSTRUCTIONS:

1. Orient your gel with the wells on the left side. The top well is number 1.
   
   
   
   
   
2. Complete the diagram above to assign colors and wells to each member of your group. Some colors may be repeated, but be sure each color is used at least once.
   
3. Fill the pipet with 10 microliters of food color.
   
4. Carefully place the tip of the pipet into the well. Keep the pipet steady so that you donÌt poke a hole through the well! Slowly fill the well with all the food color in your pipet.
   
5. Make sure the area around the electrophoresis chamber and power source is completely dry.
   
6. Follow your teacherÌs instructions for starting the electrophoresis.
   
7. When the electrophoresis is complete, carefully remove the gel and place in a plastic bag labeled with your name.
   

ANALYSIS OF RESULTS NAME____________________

1. Prepare a sketch of your gel. Use colored pencils to show the colors of the samples as originally loaded, and the bands that resulted after electrophoresis. Be sure to show each band in its proper position. COLORED SKETCH REQUIRED. STAPLE TO THIS PAGE.
   
   
2. How does electrophoresis separate the dye pigments?
   
   
   
   
   
3. What charge is carried by the pigments in this separation? Support your answer.
   
   
   
   
   
   
   
4. Suppose a dye separated into 4 distinct bands. Would you expect these bands to migrate further from the origin than in this separation, or less far? Explain your prediction.
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   

FOR FURTHER INFORMATION:

STAINING AND VISUALIZING THE GEL

This is normally the next step after the electrophoresis of DNA. It is necessary because DNA is not normally visible in the gel. The gel must be soaked in a staining solution that binds to the DNA fragments in the gel. The stained gel is then exposed to light, and the separated DNA fragments are seen as visible bands. (These are the bands that you may have seen in examples of DNA fingerprinting.) Each band represents pieces of DNA of different sizes. After staining, the gel can be photographed for a permanent record.

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