Most educational stores sell foam ball model kits because they are easy to assemble, reusable and replaceable. These kits are not unique, but they are effective. The size of the balls allows you to build a large model with very few components creating a visual illustration easily seen in the last row of the classroom. While purchasing enough for groups of students to work with in class may be expensive, the durability of such models will ensure the expense only occurs every five to 10 years. If you are a crafty educator, you can purchase poster paints and foam balls at a craft store and paint the balls yourself.
Paperclips have two useful qualities: they come in a variety of colors and they can be assembled easily. In addition, the school accountant would not blink at purchasing enough paperclips for a class of 30 students. Use the assembly of a paperclip model as a pop quiz. Supply each student with more than enough of each colored paperclip and a key assigning a color to each DNA component. It will allow you to test their ability to apply the concepts they have learned. Give students extra points for twisting their model into a double helix when they display their work for grading.
If you need to fill a lab period, fall back on elementary school art class and assign a cut and paste model. Use an illustration as a guide to design your own. Most word processing programs come with clip art or drawing programs containing basic shapes like triangles, squares, circles and stars. Those with artistic talents may want to draw careful puzzle pieces and print several of each component on a single sheet. Print your designs on construction paper of various colors or break out the crayons or markers and have the students color each symbol.
Candy rich holidays like Halloween, Christmas and Valentine’s Day provide an excuse for a sweet DNA model. Gummy candies and jelly beans make the best building blocks. Chocolate without a candy coating can work well, though the students may find themselves covered in sticky, melted chocolate. Red or black rope licorice works well as the backbone for the DNA molecule if you do not insist on differentiation between the phosphates and ribose sugars of the backbone. Assemble the model with toothpicks and advise the students to snack after the model is complete. The inevitable sugar high will make you less popular with the other teachers, but remember, you can indulge your sweet tooth too.