West Junior High School
Lawrence, KS 66049
Stevenson High School
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 (per group)
- 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.
Follow all guidelines for safe use of 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
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
- Orient your gel with the wells on the left side.
The top well is number 1.
- 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.
- Fill the pipet with 10 microliters of food color.
- 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.
- Make sure the area around the electrophoresis
chamber and power source is completely dry.
- Follow your teacherÌs instructions for
starting the electrophoresis.
- When the electrophoresis is complete, carefully
remove the gel and place in a plastic bag labeled with your name.
ANALYSIS OF RESULTS NAME____________________
- 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.
- How does electrophoresis separate the dye pigments?
- What charge is carried by the pigments in this
separation? Support your answer.
- 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: If
the samples were DNA instead of food color, what would be done
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.