Teaching DNA structure

The first class I do with every new batch of M.Sc students is on structure of DNA. Every year I struggle to get the concepts across. Accustomed to memorizing and believing that the DNA, as shown in the text book, is a 2-dimensional rigid structure, it takes a lot of effort to demolish these myths. At the end of it I am not even sure whether I demolished the myths and made them realize that the DNA is a dynamic 3-dimensional structure.
There are two concepts that I find exceptionally difficult to get across:
1. The double-helix is a consequence of polymerization.
2. The major and minor grooves arise as a consequence of inherent asymmetry in the double-helix structure. The glycosidic bonds are at 120 degrees. If they had been at 180 degrees, it would have been a symmetric double-helix and consequently the grooves would have been equal.
I do lot of crochet and decided to use it to illustrate both these points. Anyone who does crochet or knitting will realize that the first two lines are the most difficult to do. In crochet when we make a long chain, it has a tendency to wrap itself into a helix shape. Similarly, in knitting, the first two lines will always wrap themselves in a helix. So here is my model of DNA using crochet.

It is very simple. I made a long chain. Then I started working on the first row using treble crochet (wrap the thread twice around the needle and draw the hook through the chain such that you will have four loops on the hook,  bring the yarn over the hook and draw hook through first 2 loops, yarn over and draw the hook through 2 loops, yarn over and draw the hook through remaining 2 loops), ch, treble crochet till the row ended.  As one does this, the crochet pattern will start forming a helix. And since the stitches are at 90 degrees, the grooves formed will be equal in size.
I used this yesterday to illustrate my point on DNA. I like to think that the students got the point. I will know only when I correct the answer scripts.