Subject: Why does DNA have an helicoidal shape ?

Hi ! I am a secondary school student in Portugal. My school is specialized 
in biology, having a garden with squite a number of exotic spieces, and 
has cooperation agreements with various portuguese science institutes. So, 
I am, wether I like it or not, immersed in biology and genetics. My father 
is a math teacher at the same school. Recently he and my biology teacher 
have had a discussion as to the reason DNA is helicoidal in shape. My 
teacher says its because of the different weights of each of the bases, 
while my father sees in it a manifestation of a deeper principle, 
involving the golden mean and the Fibonacci sequence. I have been assigned 
an investigation work about this. Are you able to help me, please ? You 
would be of great assistance.

Re: Why does DNA have an helicoidal shape ?