The code of life turns out to be an enigma


When I get the opportunity, I love spending time in local schools talking about science and trying to get young people engaged. Inevitably, one of the questions I get a lot is ‘Why did you pick biology?’ There are many answers to that question, but one of the silliest sounding is probably ‘I wanted to know the truth’. 

The biology teacher I had from Year 10 until I took my A-levels was a formidable woman, and an amazing teacher. She always hated giving us the simplified version of a biological concept and would tell us what the syllabus said before proceeding to tell us what actually happened. The result was that I spent four years being more and more excited by how much there was that I wasn’t being told. Somewhere in my head I thought that if I studied biology for undergrad I would finally find out what was really going on.

Of course nothing is that simple. For one thing, scientific dogma is being overturned and rewritten all the time. This is old news (nearly 6 months old to be exact) but it excites me because it is contrary to an immovable fact that I was taught from a young age.

As we’re taught at school, our bodies – and that of every other living organism – contain all of the information we need to build a new human in two forms of genetic molecule: DNA and RNA. Four different bases (well, five if you consider them together) form a code for twenty different amino acids, and these make up all of the proteins we need. This code is very well preserved between organisms, such that you can take a human gene and express it in a mouse. With virtually no exceptions, all living organisms use DNA to pass on the handbook of life from one generation to the next. Other nucleic acids have been made in the past, but just didn’t function the same. Until now…

In April the MRC Laboratory of Molecular Biology at the University of Cambridge made six different nucleic acids that replaced ribose or deoxyribose with a different sugar or even a non-sugar molecule. These include LNAs (which you might have encountered while doing really specific PCR), HNAs, CeNAs, ANAs, FANAs and TNAs. Of course, a normal DNA polymerase won’t copy information from DNA into one of these new nucleic acids (collectively called XNAs or xeno-nucleic acids by the group), so a key first step was engineering an enzyme that could. The original XNAs copied information back and forth via DNA in much the same way in which a retrovirus like HIV transcribes it’s genetic information into DNA and then back to RNA. 

This work is particularly interesting because of its implications for the various theories of abiogenesis (the origins of life). If other nucleic acids can function in the same way as DNA and RNA it makes it more likely that RNA was simply the first nucleic acid to arise, rather than the ‘optimal’ choice. It suggests that the use of RNA and DNA is an artefact of the evolutionary path we have taken, rather than a functional constraint.

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Pinheiro, V.B. et al (2012)
Synthetic Genetic Polymers Capable of Heredity and Evolution
DOI: 10.1126/science.1217622

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