A Hands-On Approach to Teaching the DNA Structure and FUNCTIONReturn to Biology Index
Carter, Linda DuSable High School
Objective: To understand the structure of DNA and the way in which DNA duplicates by building simple models of DNA and its components. Apparatus Needed: Large and small paper clips, 5 cm lengths of colored pipe cleaners, styrofoam blocks. Recommended Strategy: 1. Suggested use of materials: Large paper clip to represent deoxyribose sugar Small paper clip to represent phosphate group Yellow pipe cleaner - adenine base White pipe cleaner - thymine base Red pipe cleaner - guanine base Orange pipe cleaner - cytosine base 2. To form a nucleotide, hook a large paper clip to a small paper clip. Then take a short piece of pipe cleaner and fasten it to the center of the large paper clip. Remember what each of these represents. 3. Put half of your nucleotides to one side (two of each color). These will be used later as your free nucleotides. Line up the remaining nucleotides in one row and write down their order, then determine what the other side of the ladder would have to be to match. Do this about three times to familarize yourself with the order in which the bases pair. 4. Make a flat model of DNA, using the nucleotides you have before you, hook half the clips together (using one of each color), making sure the large and small clips alternate to form one side of the ladder. Using the four remaining nucleotides, match the bases in proper order, hook the pipe cleaners together and then hook the clips together to form the sides. 5. To show replication, unhook the pipe cleaner bases from each other to form two chains. Now using your free nucleotides that you put to the side, match them in their proper order and fasten the bases and paper clips together to form two DNA molecules. 6. To make a three-D model, use two pieces of styrofoam and one of the flat DNA models. Straighten out the two paper clips at each end and press them into the styrofoam strips. Hold a styrofoam strip in each hand, stretch out the model, and twist slightly to give a spiral staircase effect. Part II: mRNA STRUCTURE and TRANSCRIPTION Objective To use the DNA model to build a model of mRNA which will demonstrate its structure and the way it is formed by transcription. Apparatus Needed: Models from Part 1, the same materials, plus large colored paper clips to represent ribose, and green pipe cleaners to represent the uracil base. Recommended Strategy: 1. Use the materials to form nucleotides of mRNA, at least two of each of the four bases. 2. Use the flat model of DNA from Part 1 and your mRNA nucleotides to demonstrate transcription. Unhook your flat molecule at its bases. Match the mRNA nucleotides in their proper order (keep in mind that thymine is replaced by uracil). Evaluation For a follow up assignment write a report describing the structures of DNA and mRNA and the processes of replication and transcription.