Dangerous Curves

Published in Protocols & Methods

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I’m a sucker for beauty in science even if the immediate application is a little unclear, and to my mathematically leaning brain the paper1 that has just come out in Nature Nanotechnology is a real beauty.

DNA isn’t just the parchment upon which our genetic information is scribbled but has become over the last decade or so the molecule of choice for those nonotechologists who are interested in creating self assembling molecular systems. It’s just great for it. The complementarity of one strand with another means that you can build double strands of DNA with sticky ends that will assemble themselves into all kinds of shapes. Cubes2, interlocking rings3, even tiles that can be used for computing answers to problems that are ‘difficult’ to do digitally4. There is a serious point behind thee studies but I have to say they are great fun too.

The new Nature Nanotechnology paper from Dongran Han, Suchetan Pal, Yan Liu & Hao Yan of Arizona State University has got DNA assembled into one of the favourite shapes of mathematicians, the Möbius strip. Möbius strips have the exotic property having only one edge and one side and you can make one right now by taking a long thin strip of paper, forming it into a loop but twisting one strand a half turn relative to the other before taping them together.

And that is what the Arizona team has done with a strip made out of 11 double strands of DNA looking for all the World like the data cables that used to be so common but are now being replaced by USBs. And they have the atomic force microscopy pictures to prove it.

Fig 2.jpg

Adapted from Fig. 2 of Han, Pal, Liu & Yan1

That though isn’t enough for these researchers. Because of the way that the DNA strands are constructed they are able to add to the Möbius DNA shorter pieces of DNA which disrupt the lateral interactions of the strand; the equivalent of taking scissors and cutting along the length of a paper strip.

Here things get weird as, just like the paper strip, slicing down the middle of the DNA ribbon result in a DNA loop twice as long as the original Möbius loop but with a double twist instead of the original single. Better yet, disrupting the ribbon a third in from the edge produces two loops, one Möbius and one not, separate but interlinked.

Fig 3.jpg

Adapted from Fig. 3 of Han, Pal, Liu & Yan1

It’s beautiful and delicate science for which I hope some practical application can soon be found so that the protocols of the Arizona group can be taken up more widely.

1 Han, D., Pal, S., Liu, Y. & Yan, H. Folding and cutting DNA into reconfigurable topological nanostructures. Nature Nanotechnology (2010) doi:10.1038/nnano.2010.193

2 Chen, J. & Seeman, N. C. The synthesis from DNA of a molecule with the connectivity of a cube. Nature 350, 631-633 (1991).

3 Mao, C., Sun, W. & Seeman, N. C. "Construction of Borromean rings from DNA. ":http://www.nature.com/nature/journal/v386/n6621/pdf/386137b0.pdf Nature 386, 137-138(1997).

4 Mao, C., LaBean, T. H., Reif, J. H. & Seeman, N.C. Logical computation using algorithmic self-assembly of DNA triple-crossover molecules. Nature 407, 493-496 (2000).

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