Though it took decades of careful research to discover the exact components and shape of the DNA molecule, it is possibly the easiest genetic concept to learn. The DNA molecule is orderly, pairing its nucleotides according to specific rules and twisting into a distinctive double helical shape. This project tests students' ability to problem solve to make a correct DNA model. Instruct students to build a model based on the following rules: Phosphates connect only to ribose sugars. Ribose sugars connect to two phosphates and a single nucleotide. The nucleotide guanine only connects to cytosine. The nucleotide adenine only connects to thymine. The completed DNA molecule resembles a ladder with nucleotide pairs making up the rungs.
When building a DNA model, many teachers and students simply twist the final product into a double helical shape. In reality, the exact angle of binding and the number of base pairs required to make a single turn are fixed. For this project, a toothpick-and-foam-ball model will allow the students the greatest amount of control. When originally researching the DNA molecule, Rosalind Franklin and Raymond Gosling discovered that each base pair rises at a 36-degree angle to make a 360-degree turn every 10 base pairs. Do not tell the students how to build the model; only indicate that it should be precise. Combine the mathematical precision of this project with the problem solving directions in the above project to create a complex project for a final exam.
Test the students' understanding of DNA structure and nucleotide pairing by providing them with half of a DNA code. The students must assemble the phosphate/ribose backbone and the nucleotide sequence they have been assigned. In addition, they must construct the mirror side of the DNA molecule, making correct nucleotide base pairs. Where the above projects allow them to construct the code at random, this project requires them to replicate the code exactly. This project is useful as a hands-on exam.
DNA replication is known as a semi-conservative process because one side of the parent DNA molecule goes to each daughter DNA molecule. The students should assemble a DNA molecule at least 30 base pairs tall and then “unzip” the bottom 10 base pairs and the top 10 base pairs. By attaching a new set of nucleotides on a phosphate/sugar backbone to the top right leg and the bottom left leg of the DNA model, the students will be replicating the path of DNA replication. This project tests the students' understanding of replication and reinforces nucleotide pairings.