by Mike Mongan
The Unit of Universe saddle offers and inexpensive and effective way to demonstrate the form of the DNA (dioxyribonucleic acid) molecule. In several other places in this website, the method of removing the outer edge as a continuous ribbon has been described. The circular ribbon can be twisted into a double helix connected at both ends as shown in the illustration from the Basic UU article.
Figure 8 THE CIRCULAR RIBBON
The method is this. Open up the continuous ribbon as shown. Notice that it is not a Mobius strip. It has two distinct faces, an obverse and a reverse. Pick the part in either your left or right hand as the starting spot and let the rest hang free. Next we will be putting the ribbon face to face. To do this, pick either the obverse or reverse. It may get confusing and you might want to take a marking pen and simply put a line on one side to keep it straight. From the starting spot, put the lined side face to face and gradually work all the way down to the other end. Notice as you go that the ribbon is coiling like a spring or a snake. You may need to untwist the ribbon as you get toward the end to get it to fall into place. When you are finished, you should have a neat double coil of ribbon with loops at either end. Suspend it from either end and you will see the dual helix form used by DNA. Since the ribbon is paper it may tear. Just tape it together again. Be sure to keep from mixing the faces when you do . It is fascinating that in a cell, the DNA molecule can be so twisted up and yet separate for cell division. This demonstrator shows how much of that process is inherent in the nature of this form. It is also interesting to ponder that this demonstrator was serendipitously derived from a saddle used to represent basic atomic processes.
Demonstrating the DNA Molecule