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Wiki Education Foundation-supported course assignment[edit]

This article is or was the subject of a Wiki Education Foundation-supported course assignment. Further details are available on the course page. Student editor(s): Maurogarcia21, Bailey-Raye, Hmw3425.

Above undated message substituted from assignment by PrimeBOT (talk) 05:25, 18 January 2022 (UTC)[reply]


An image of Z-DNA would be nice here, perhaps even a picture comparing all three.

  • Done. I created these images with a fine piece of software in Linux. Feel free to make comments. Thorwald 05:55, 19 Mar 2005 (UTC)
  • The rotating image looks like a right-handed helix to me. 15 Sep 2008 —Preceding unsigned comment added by (talk) 12:01, 15 September 2008 (UTC)[reply]
    • No. It is a left-handed helix. It is just rotating towards the right. Thorwald (talk) 01:09, 16 September 2008 (UTC)[reply]

Citation needed.[edit]

Will some expert kindly provide a source for the sentence quoted below, so that I can reach my goal of paring down the Citation Needed references on the following page?

While no definitive biological significance of Z-DNA has been found, it is commonly believed to provide torsional strain relief while DNA transcription occurs.[citation needed]

Sincerely, GeorgeLouis 06:30, 29 October 2006 (UTC)[reply]

  • A PubMed search for almost any paper published by Alexander Rich or P. Shing Ho should provide you with all the references you need. Dr. Rich "discovered" Z-DNA (in 1979) and is arguably the leading expert on it. He continues to publish to this day. Dr. Ho was Rich's postdoc and is now a professor (and chair) of biochemistry and biophysics. He also actively publishes on DNA to this day.--Thorwald 18:07, 29 October 2006 (UTC)[reply]


Other users tried to use your table with the information of the different DNA-Isoforms in the German Wikipedia but I noticed that there were quite big differences to the values that Voet et al: Fundamentals of Biochemistry (2006) gives. So it would be nice to know where you have the data from before we quote them. I did not find any specific citations. greetings --hroest 14:03, 13 February 2007 (UTC)[reply]

That table has been hanging around on the article for aaages... i have no idea who the original author for it was. While it would be nice to find the original source i would say it would be worthwhile to update the table with a reliable current reference anyway. - Zephyris Talk 15:39, 13 February 2007 (UTC)[reply]

I have the book, DNA Structure and Function by Richard R. Sinden (1994) and chapter 5 ("Left-Handed Z-DNA") has some more tables with references. I will add them once I get a bit more free time. --Thorwald (talk) 09:00, 8 March 2011 (UTC)[reply]

  • Actually, there is quite a bit of information on Z-DNA in that chapter (should be). This article could be expanded quite a bit just from the information in this chapter. I'll get on it. --Thorwald (talk) 09:01, 8 March 2011 (UTC)[reply]

X-ray diffraction vs crystallography[edit]

The following statement in History is a little confusing... "Z-DNA was the first crystal structure of a DNA molecule to be solved (see: x-ray crystallography). It was solved by Alexander Rich and co-workers in 1979 at MIT.[1] "

I've always believed (possibly erroneously) that X-ray crystallography was a more general term. If this is the case, then wouldn't Watson and Crick's analysis of Franklin's X-ray diffraction of a DNA crystal in the 50's be "the first crystal structure of a DNA molecule to be solved"? PS I'm not trying to be smart here, I just want clarification. PRH969 14:14, 22 September 2007 (UTC)[reply]

  • Wasn't the difference that Franklin's structure was from fiber diffraction, whereas, Rich's structure was from a true crystal? Also, the technique of x-ray crystallography produces much higher resolution than the technique of fiber diffraction. I believe that before 1979 all DNA structures had been determined using fiber diffraction; Rich, with Z-DNA, was the first to use x-ray crystallography to determine his structure. I am interested in getting this right and, if need be, clarifying the above sentence. --Thorwald 22:42, 22 September 2007 (UTC)[reply]
    • Actually, I believe my above assumptions were correct. I will be updating the article to reflect that (and include references, of course). --Thorwald (talk) 09:37, 8 March 2011 (UTC)[reply]

Discovery of Z-DNA[edit]

I commented out a sentence that was added today by another user (in the "History" section). The sentence in question reads as follows: "Left handed DNA was discovered by Robert Wells and Charles Cantor in 1970 when they observed that a repeating polymer of d(I-C)-d(I-C) displays an inverted circular dichroism spectrum compared with other sequences". The link the user pointed to (Well & Cantor) was really just a suggestion that this polymer could adopt a left-handed conformation under specific conditions (based on the X-ray diffraction pattern and CD spectra). However, much later, Sutherland and Griffin (1983) found that the polymer actually adopted an unusual non-B-DNA right-handed configuration (called "D-DNA"), not a left-handed configuration. Note also that the idea of a left-handed DNA helix had been around for a long time prior to its discovery. --Thorwald (talk) 19:37, 20 October 2010 (UTC)[reply]

  • After further research, I have concluded that, indeed, the above statement was incorrect and I have removed it altogether from the article. --Thorwald (talk) 09:40, 8 March 2011 (UTC)[reply]

Thorwald: I just wanted to bring to your attention two points. One - you're correct that there was some discussion in the literature about whether d(I-C) adopts left- or right-handed DNA. This issue was brought up by Arnott, S., Chandrasekharan, R., Hukins, D. W. L., Smith, P. J. C. & Watts, L. J. (1974)J. MoL BioL 88, 523-533. However, subsequent work from the Sasisekharan lab (of Ramachandran plot fame) (please see Gupta, G., Bansal, M. & Sasisekharan, V. (1980) Proc. Nati Acad. Sci. USA 77, 6486-6490; Gupta, G., Bansal, M. & Sasisekharan, V. (1980) Int.J. Biol MacromoL 2, 368-380) suggested that the Arnott et al. idea of D-DNA was stereochemically unaccesptable. Sasisekharan and colleagues subsequently examined the inosine-cytosine polymer, and found that it was consistent with left-handed DNA (please see Left-handed helices for DNA: studies on poly[d(I-C)]. Ramaswamy N, Bansal M, Gupta G, Sasisekharan V. Proc Natl Acad Sci U S A. 1982 Oct;79(20):6109-13.) The Sutherland and Griffin paper you mentioned did not actually look at inosine-cytosine; they looked at the CD spectrum of a GC polymer that was found by Pohl and Jovin to be "inverted". In fact Sutherland and Griffin conclude that the CD spectrum inversion is a valid method for examining handed-ness of DNA. Therefore, I think it is fair to state that the Wells work was the first that used experimental data to support the idea of left-handed DNA. I'd like to thank you for your interest in this fascinating subject. Raviriyer (talk) 15:45, 16 February 2015 (UTC)[reply]