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Cool Tool: Rubber Tubing Model of Supercoiled DNA
Type: Model
Topic: Supercoiling of DNA
Grade Level: High School
Contributor: Don Lightfoot
School: Eastern Washington University, Cheney, WA
Purpose: To explain one aspect of DNA structure, supercoiling.
Materials: A piece of rubber tubing 1-4 feet long, a short stick or rod to connect the two ends of the tubing.
Methods: The tubing represents a double-stranded length of DNA. Draw two lines along the length of the tubing on opposite sides to represent the backbones of the two DNA strands. Draw base pairs as short, perpendicular lines all along the length of the tubing. Place a short stick or rod into one end of the tubing. Taking care not to introduce any twists into the tubing, place the rod into the other end of the tubing to connect it into a (flat) circle. The closed circle made by the tubing represents relaxed/non-supercoiled DNA, such as a nicked plasmid.
Disconnect the ends and twist one end on its axis several revolutions until the tubing curls up on itself. Then reconnect the ends. This is supercoiled DNAóthe only biologically active form. Additional details about supercoiling can be given depending on the sophistication and background of the class.
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last updated 06/15/04