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The Arizona Hedgehog
Cactus:
Endangered Species or not?
Lesson 5: Electrophoresis
Analogy
Adapted from the Monsanto Biotechnology Education Project
Purpose:
The students will participate in an activity which will demonstrate
visually how DNA electrophoresis through an agarose gel works.
Time:
One 50-60 minute class period
Materials Preparation:
- Campus playing field, gym or large classroom
- Old tires, cones, desks, chairs, etc.
- Candy (reward)
- Overhead transparency of "A DNA Agarose Gel"
- Student copies of "Gel Electrophoresis and Analysis"
Student Objective(s):
- Describe how an agarose gel separates DNA fragments according
to size.
- Explain how differences in DNA sequence result in different patterns
of bands on a DNA electrophoretic gel.
Lesson Plan:
- Set up the obstacle course on a playing field, gym or in a large
classroom prior to class.
- Write the following analogy on the board.
- G, A, T or C = 1 student
- A 3-base fragment = 3 students holding onto each other
- A 15-base fragment = 15 students holding onto each other
- Electric current = Candy reward at finish line (the driving force)
- Gel matrix = Obstacles (tires, desks, chairs, etc.)
- Loading wells = Starting line
- Explain the rules of the activity: Students, in groups of one,
three or fifteen, gather at the starting line and hold on to each
other in a line. They are not to release each other at any time
during the race. They are to move as quickly as possible through
the course and the first group to the finish line gets the candy
reward. The teacher marks the stopping point of each group when
the winning group finishes. These stopping points represent gel
bands.
- Perform the activity.
- Lead a class discussion to develop the following points: DNA is
negatively charged and fragments travel through the agarose gel
from the wells toward the positive end of the gel, driven by electric
current. The DNA fragments must travel through the matrix of tangled,
agarose molecules. Larger fragments move more slowly through the
matrix and so don't move very far from the wells. Smaller fragments
can easily "slither" through the agarose molecules and quickly move
toward the positive end of the gel and are represented as bands
farther from the wells. Show the transparency of "A DNA Agarose
Gel" to explain the length of the fragments in each of the bands
and the distances travelled.
Supporting
Materials:
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