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:

(1) Set up the obstacle course on a playing field, gym or in a large classroom prior to class.

(2) 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
  

(3) 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.

(4) Perform the activity.

(5) 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:

• "A DNA Agarose Gel" - Overhead
• "Gel Electrophoresis and Analysis" - Lab Sheet
• "Gel Electrophoresis and Analysis" - Answer Key
  
  
  
  

Science Education Connection Department of Biochemistry The University of Arizona May 1, 1997 warder@u.arizona.edu http://biology.arizona.edu/sciconn/lessons/alongi/ All contents copyright ©1997. All rights reserved.