Create the "Backbone"

• 1). On the first piece of fishing line, string alternating pieces of pinwheel and ziti pasta, starting and ending with a pinwheel. Make sure the pinwheels on the ends are tightly tied so they do not slip off.
  
  
• 2). Repeat with the second piece of fishing line, constructing a second strand that is identical to the first.
  
  
• 3). Examine your model. The two types of pasta represent the two alternating molecules of the DNA "backbone"--a phosphoric acid and a sugar (deoxyribose).
  
  

Assemble the Base Pairs

• 1). Assign one pipe cleaner color to represent each of the four organic bases present in DNA. For instance, you might make red represent adenine; yellow, thymine; blue, cytosine; and green, guanine.
  
  
• 2). Because these organic bases only bond to each other in prescribed combinations, twist each adenine segment together with one thymine segment, and each cytosine with a guanine. These would correspond to red-yellow and blue-green pairs in this example. You will need the same number of total pipe cleaner pairs as you have ziti on each backbone strand.
  
  
• 3). Line up your two backbone strands so they are parallel. Attach one base pair to each pair of ziti, so that the model forms a ladder shape with the pipe cleaners as the rungs. The order of the base pairs does not matter and should be random; the colors need not alternate.
  
  To construct an accurate model, be sure to pair adenine only with thymine, cytosine only with guanine, as these are the only combinations that occur in nature.
  
  
• 4). Twist your ladder so that it resembles a corkscrew. This shape is called a double helix and is the natural conformation of a DNA molecule.