# [Avogadro-Discuss] Right-Handed Z-DNA?

Hi,

We are using Avogadro version 1.2.0 to build a single-stranded adenine-adenine Z-DNA dinucleotide with the Build extension.

Our preliminary understanding is that the Z-DNA generated by Avogadro has a right-handed conformation. However, Z-DNA is generally described as having a left-handed structure. So, we find it curious that Avogadro builds a right-handed DNA strand by default. Appended, you will find our simple criteria to determine if the Z-DNA from Avogadro is right-handed.

Does anybody know about the handedness of the Z-DNA generated by Avogadro?

Thanks,

Eric Beyerle

P.S., Here is our criteria to determine right- and left-handed DNA:

It is pedagogical and useful to visualize the coordinate system using the traditional mnemonic of the right-hand rule. When viewing the single-stranded dinucleotide with the 3' base on the top and the 5$’$ base on the bottom, one may take one’s index finger as pointing along the in-plane vector of the 5’ nucleotide base as described above and the other three fingers as pointing along the in-plane vector of the 3’ nucleotide: considering one’s thumb points upward, the conformation is right-handed if the index finger rotates counter clock-wise to align the three other fingers.

Otherwise, the conformation is left-handed (\\varphi < 0). These definitions agree with the usual right- and left-handed conventions used to classify biological forms of single- and double-stranded DNA (A-, B-, and Z-DNA, specifically).​

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It is almost certainly a bug.

You’ll note that the A/B/Z popup only changes the number of bases per turn. Certainly other differences (sugar pucker, etc.) will also be incorrect for Z.