XNA - expanding problems

July 2012
DNA double helix Image by By National Human Genome Research Institute (http://www.genome.gov/pressDisplay.cfm?photoID=96)
[Public domain], via Wikimedia Commons 
Not content with exploring the vast world of DNA and the even more vast world of the RNA molecules produced by DNA, scientists have now taken to engineering their own weird analogues.

The data of the 'genetic code' are enciphered by DNA in sequences of four 'nucleic acid base' molecules. These four bases pair up with each other in specific ways to form the 'rungs' of the famous double-helix DNA 'ladder'. It's the bases which provide the template from which the cell's movers and shakers, the RNA molecules, are reeled off.

Up until now, Biotechnology has busied itself by playing around with the base-pairs to instill its own, commercially useful, features into cells.

But DNA and RNA have more to their structure than the bases. The 'D' bit of DNA and 'R' bit of RNA refer to the backbone of the molecules to which the bases are attached. The backbone is a chain of 'D' or 'R' sugar molecules.

Besides anchoring the bases in line, the chain of sugars provides DNA and RNA with their extreme flexibility, 3-dimensional structure, and ability to link up with the enzymes involved in their function.

What better fun that to engineer novel sugars (let's call them X) and build them into a chain with bases attached (let's call it XNA). Molecular scientists were delighted to discover that, not only could XNAs be made from several weird sugars, but that these could mimic DNA: they can store and reproduce genetic information, evolve, and stick to specific proteins. New weird bases have even been added to the old code.

XNAs have many qualities very different from DNA and RNA. They're invulnerable to enzymes extreme acids and alkalis: they're “tough as nails”, “bullet-proof”. And, presumably they've already been tested on life because they “have low toxicity and low immunogenicity”(Hollinger). Further chemical modification promises to further improve their stability and the way the body handles them.

By now, you might be asking why anyone would want XNAs?

Well, the published paper describing how XNAs are created, notes in its introduction that they “would open up applications ranging from biotechnology to materials science” which expands in its conclusion to “tailor-made chemistries for applications in biotechnology and medicine”.

Because of their ability to bind very specifically to proteins and their small size which will allow increased tissue penetration, plus their invisibility to the body's defense mechanisms, XNAs are expected to have exciting diagnostic, therapeutic and analytical applications.

More imaginative scientists suggest XNAs may ultimately lead to the synthesis of novel forms of life.

This research isn't an outrageous Craig Venter baby (see CRAIG VENTER'S WEIRD WORLD - July 2012). It was funded by the Medical Research Council, the European Framework Programme, and the European Science Foundation.


Nature has limited herself to DNA and RNA for a reason: these molecules form part of the interconnected and coherent wholeness within the organism, between organisms, within ecosystems and throughout the world. This is the way, Nature has created a healthy, evolving system. Anything which doesn't mesh with the whole is a disease.

Put another way, Nature is purposeful, not an ego-driven smarty-pants doing things just because it can.

The research of XNAs is described in lyrical terms by one blogger as expanding the chemistry of life in new uncharted directions and expanding the palette of molecules that carry genetic information. Since we can't get our heads round DNA, and RNA is proving even more mind-blowing, why expand the problem?

It seems we are unable to learn from experience. XNAs are being promoted as the ultimate biosafety tool: they are, we are assured, unable to go feral and run amoke through wild populations because they will sit invisibly behind a firewall in a world ruled by DNA and RNA, unable to exchange their genetic information with the living things around them.

Remember the characteristics of XNAs described above: they can evolve ... reproduce ... stick to living proteins ... avoid immune-system detection ... avoid natural decomposition ... Oh, and another thing, XNAs are produced by using rounds of DNA-to-XNA and XNA-to-DNA synthesis using enzymes discovered by random mutation. The potential for interaction with and disruption of the natural world is plainly there.

If you believe XNAs will be safe to have inside you, in your food, in your environment, in microbial life, in viruses, and anywhere else you can think of with all those features, you'll believe anything.

  • Vitor B. Pinheiro, et al., lead scientist Philipp Holliger, 2012, Synthetic Genetic Polymers Capable of Heredity and Evolution, Science 336
  • Synthetic XNA molecules can evolve and store genetic informaiton, just like DNA, http://blogs.discovermagazine.com, 19.04.12
  • Ruth Williams, Synthetic Genetic Evolution, http://richarddawkins.net, 23 04.12
  • Ian Sample, DNA alternative created by scientists, Guardian, 19.04.12

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