A Hands-on Approach to Teaching about DNA Structure and Function

Abstract

In light of the ever-increasing importance of genetic research to the ordinary citizen as well as to the biologist, it seems imperative to ensure that our biology students gain a thorough understanding of the structure and function of DNA. This instruction should include the way in which DNA replicates and the process of transcription in which the codes for various proteins are passed on to the ribosomes by the mRNA. We became dissatisfied with the laboratory activities available at the high school level for developing concepts in molecular genetics. The students who appeared not yet able to carry out formal operational thought were having a particularly difficult time conceptualizing the structure of DNA. We thought that a more concrete activity would allow our students to meaningfully visualize the structure and function of DNA. The laboratory investigations illustrated here seemed to accomplish these goals. Our goal was to develop a manipulative activity using inexpensive but graphic materials. The materials used were two sizes of paper clips, an assortment of colored pipe cleaners, and flat styrofoam sheeting, such as that used for building insulation. Advance preparation consisted only of cutting the pipe cleaners into approximately 5 cm lengths, spray-painting part of the paper clips, and cutting the 2-cm-thick styrofoam sheeting into pieces approximately 3 cm by 7 cm. Be sure to have plenty of paper clips available for each student. The investigations can be used before or after class discussion of DNA structure, as all the information needed is included in the Background section of the paper supplied to the student. The format of the investigations was patterned after the Extending Discretion Approach (Leonard, 1980; 1981), but the steps are very specific in order to make sure the desired results are obtained. Allowing the students to watch what happens with the models appears to aid in their understanding of both replication and transcription. The first part of the investigation has the student make model nucleotides and then form them into a model of DNA to show how the nucleotides act as building blocks. Students demonstrate replication using the flat DNA model and free nucleotides and make a somewhat three-dimensional model to visualize the double helix. The flat and twisted DNA models are shown in Photo 1 and Photo 2 respectively. The second part of the lab deals with mRNA and has the students again form nucleotides and make a model using slightly different materials, thus demonstrating the differences between mRNA and DNA. They demonstrate transcription using the flat DNA model and the mRNA nucleotides. Each part of the investigation may take a full class period, so they are separate activities. After completing the investigation, the students write a report summarizing what they have learned about the structure and function of the two compounds. The actual printed laboratory procedures given to the students are shown in Boxes 1 and 2. In working with the student during Photo 1. The flat model of DNA creates a concrete visual aid for understanding DNA structure. Photo 2. With a twist of the wrist, an idea of the double helix is suggested.