DNA Structure and Supercoiling: Ribbons and a Yo-Yo Model

Abstract

The double-helical structure of DNA is a pop cultural icon. Images of the DNA molecule appear in newspapers, popular journals, and advertisements. In addition to scientific instrument sales, the aura surrounding the central molecule of life has been used to sell everything from perfume to beverages and is the inspiration of items ranging from jewelry to staircases and from paintings to sculpture. The 50th anniversary of the discovery of the structure of DNA (1953–2003) highlighted the dramatic change in both the scientific and public perception of this central biological molecule. The helical structure and physical features of DNA are the topic of classroom instruction from the high school level through post-graduate training. The major structural features of the DNA molecule are presented in a new “model for everyone” based on a printed ribbon. Tertiary and quaternary nucleic acid structure, including supercoiling, are demonstrated using a yo-yo model; the replication fork required for nucleic acid replication and transcription can also be demonstrated using this model. These simple models can be adapted for use in high school classrooms or for university and graduate course instruction.