Talk:two-start

Tea room discussion

Note: the below discussion was moved from the Wiktionary:Tea room.

These two adjectives seem to have a mathematical (topological?) meaning, but because the words themselves are very common I am having difficulty in researching them. I have added the same citation for them in the meantime (see e.g. Citations:two-start). Help from a mathematician would be appreciated. SemperBlotto 09:59, 20 May 2008 (UTC)

Looking over the hits for "two-start helix", I thought I was beginning to understand the basic concept, but then I found this and was back in the dark again. -- Visviva 10:46, 20 May 2008 (UTC)

This fairly lucid explanation may be helpful. Anyway, I'm not a mathematician, so that's as far as I go. -- Visviva 11:06, 20 May 2008 (UTC)

Judging from this or this it appears to be about the number of interlocking helices, in that a n-start helix would consist of n separate helical curves which twist around the same cylinder. If so, a two-start helix would (in an abstract sense) be the same as double helix, but then as our entry on the latter claims, if this in molecular biology is restricted to the actual DNA helix, well, then another word would have to be used for arbitrary "double helices"... \Mike 13:01, 20 May 2008 (UTC)

Re: "a two-start helix would (in an abstract sense) be the same as double helix": I don't think so, no. You're thinking that DNA is a double helix because it has two parallel strands; but I don't think that's what "double helix" means. I think DNA is a double helix because it's a helix (specifically, apparently, a two-start helix) around a center-line that is itself, in turn, a helix. So the whole thing is very twisty. —Ruakh_TALK 18:50, 20 May 2008 (UTC)

I do not agree, mainly based on the first of the links :). There, the figures A and B both depicts a helix which is in itself twisted into a larger helix, but A is specifically called "one-start" (actually "one-start solenoidal") while B is called "two-start", which would fit with my interpretation. According to wp, "supercoiling" seems to denote the very same phenomenon you described. \Mike 19:09, 20 May 2008 (UTC)

I'm not disagreeing with your interpretation of "one-start" and "two-start", only with your interpretation of "double helix". However, w:Double helix suggests that I'm wrong anyway, so I guess it's moot. :-)   —Ruakh_TALK 21:13, 20 May 2008 (UTC)

Thanks. I've had a go. SemperBlotto 13:48, 20 May 2008 (UTC)