DNA is the fundamental building block of genetics. There are several ways students can go about building models of DNA. The double helix structure of DNA can be modeled with materials ranging from toothpicks and paper to licorice and gumdrops. The key components of a DNA model are the long strands on the side, made of sugars and phosphate groups, and the bases which connect the strands. Students can choose to create a model that demonstrates the shape of DNA simply or opt for more complexity with a model that resembles paired bases that encode the DNA information.
One relatively simple and informative science fair project is the extraction of DNA from plants. An onion works well to demonstrate simple DNA extraction procedures. DNA is located in the nucleus of the onion cells so to isolate it, the cells must be broken open. Using detergent, salt and meat tenderizer, students can break down the cell membrane and the nucleus. Adding rubbing alcohol makes the DNA stick together, which leaves sticky white strands of DNA that students can extract.
Extracting DNA from a student's own cheek cell is a bit more complex than using an onion, but it can be a great way to demonstrate how DNA is present in all living things. Students swish water inside their mouths to collect cheek cells and spit the mixture into a small dish or cup. They can then use detergent to break down the cell membranes and release the DNA into the solution. Similar to the onion project, alcohol is then used to make the DNA “gel” together so it can be removed.
Gel electrophoresis is a tool used by scientists to separate DNA from other parts of the cell so it can be studied. Electrophoresis is accomplished by sending a current through a gel solution. Charged molecules will move with the current and different-sized molecules will move at different speeds. To model this scientific procedure, students can use food coloring and batteries. The different dyes will separate out as the current is sent through the gel.