"Paul P." <nomail@nomail> wrote in message 
news:web.43fb41c589e84e74d937d540@news.povray.org...
> "Bob Hughes" <omniverse@charter%net> wrote:
>> The period (second number after x,y,z) can be negative to turn it the 
>> other
>> direction. Could also use just one f_helix1 by specifying 2 as the first
>> number to double the strand.
>
> Thanks! I thought I tried putting negatives everywhere, but that certainly
> works. The only issue with using the 2 in the fhelix1 function for the two
> strand is that there doesn't appear to be a way to change phase of the
> strands. For biological correctness, DNA has alternating major and minor
> grooves (see my first example). It was simple enough to make two identical
> backbones and rotate one 120 degrees to set the proper phase.

Glad to have helped any at all.

I had a feeling it shouldn't be so symmetrical, especially after seeing all 
the variations I could find through internet searching for a picture of one. 
I chose the easiest route. Biology wasn't my favorite subject in school, 
chemistry was.  :)

Bob H

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