# The double-helix structure of DNA? **URL:** \ **Category:** Factual Questions\ **Created:** [March 8, 2011, 7:33pm UTC](https://boards.straightdope.com/t/the-double-helix-structure-of-dna/573957 "2011-03-08T19:33:05Z")\ **Posts on this page:** 6\ **Page:** 2
**Author:** ![lazybratsche](https://avatars.discourse-cdn.com/v4/letter/l/ba8739/32.png) [@lazybratsche](https://boards.straightdope.com/u/lazybratsche)\ **Post date:** [March 8, 2011, 9:59pm UTC](https://boards.straightdope.com/t/the-double-helix-structure-of-dna/573957/21 "2011-03-08T21:59:12Z")
I’m not entirely sure I follow the double/single helix debate here. But for potential clarification, and to add some more types of illustration, here are some models of A- B- and Z- dna in spacefill and wireframe, both from the [side](http://web.virginia.edu/Heidi/chapter12/Images/8883n12_13_a.jpg)and from the [http://web.virginia.edu/Heidi/chapter12/Images/8883n12\_13\_b.jpg](http://web.virginia.edu/Heidi/chapter12/Images/8883n12_13_b.jpg). ETA: Unfortunately, **Punoqllads** , it looks like google led you to a crank. That whole article seems to be by a guy who doesn’t like the fact that DNA doesn’t have the structure he thinks it should. Well, that’s nice, but he needs a hell of a lot more than that to refute decades of crystal structure determinations. ---
**Author:** ![thelabdude](https://avatars.discourse-cdn.com/v4/letter/t/dc4da7/32.png) [@thelabdude](https://boards.straightdope.com/u/thelabdude)\ **Post date:** [March 8, 2011, 10:31pm UTC](https://boards.straightdope.com/t/the-double-helix-structure-of-dna/573957/22 "2011-03-08T22:31:17Z")
> [@Sitnam](#): > > I’ll concede the double helix is called that because there are two edges, but I’m still absolutely convinced that the axis itself rotates around a second axis. Wasn’t the double helix about DNA being composed of 2 helical strands of RNA? ---
**Author:** ![Shmendrik](https://avatars.discourse-cdn.com/v4/letter/s/ee7513/32.png) [@Shmendrik](https://boards.straightdope.com/u/Shmendrik)\ **Post date:** [March 8, 2011, 10:55pm UTC](https://boards.straightdope.com/t/the-double-helix-structure-of-dna/573957/23 "2011-03-08T22:55:14Z")
> [@thelabdude](#): > > Wasn’t the double helix about DNA being composed of 2 helical strands of RNA? No, they’re different molecules. Specifically, the DNA backbone is made of phosphate and deoxyribose, while the RNA backbone is phosphate and ribose. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [March 8, 2011, 10:58pm UTC](https://boards.straightdope.com/t/the-double-helix-structure-of-dna/573957/24 "2011-03-08T22:58:41Z")
You can describe the different pictures by the difference in angle between the two strands. In the OP, the first has them arranged symmetrically, 180 degrees from each other. In the second, the angle difference is only 90 degrees, or maybe less. In **Terminus Est** ’s B-DNA link, they look like they’re maybe 120 degrees apart. The A-DNA looks closer to 180. It seems like this angle should be able to be determined from the data in the table in the A-DNA link. ETA: Interesting about the A-DNA, B-DNA and Z-DNA forms. Never came across that before. ---
**Author:** ![FluffyBob](https://avatars.discourse-cdn.com/v4/letter/f/ecb155/32.png) [@FluffyBob](https://boards.straightdope.com/u/FluffyBob)\ **Post date:** [March 9, 2011, 12:38pm UTC](https://boards.straightdope.com/t/the-double-helix-structure-of-dna/573957/25 "2011-03-09T12:38:41Z")
I have always wondered this also. lazybratsche’s illustrations seem to show the Z DNA with the ‘spokes crossed at the central axis’ version of the double helix. The two versions of double helix seem to be merely an issue of phase. Sitnam would it be possible for you to explain or find an illustration of what you mean by a second axis? It seems to me that in both versions, both helix are twisting around the same axis. Looking down on a double helix from the top we see a circle with spokes. In one version the spokes cross at the axis or center of the circle. In the other extreme (ladder wrapped around a cylinder) the spokes do not cross at the central axis and the double helix is hollow. The difference between the A DNA and the B DNA helix seems to be the extent of the center hollow. If there were two axis would we not see two circles looking down from the top? Is there another configuration I am not visualizing? ---
**Author:** ![Sitnam](https://avatars.discourse-cdn.com/v4/letter/s/6a8cbe/32.png) [@Sitnam](https://boards.straightdope.com/u/Sitnam)\ **Post date:** [March 9, 2011, 5:55pm UTC](https://boards.straightdope.com/t/the-double-helix-structure-of-dna/573957/26 "2011-03-09T17:55:50Z")
> [@RadicalPi](#): > > Are you suggesting that if you look at DNA from the top down, so that the perimeter that you see is mostly a circle, there would be no central “atrium” in DNA? Yes, but more precisely there ‘is’ an atrium because the center is empty. [Previous page](https://boards.straightdope.com/t/the-double-helix-structure-of-dna/573957.md?page=1)