Life as we know it is possible thanks to the existence of a code, an alphabet, made up of only four letters called nucleotides. When these letters combine, the renowned DNA and RNA macromolecules are formed. In DNA, nucleotides comprise a phosphate group, the bases adenine, cytosine, guanine, and thymine, and the sugar deoxyribose. In RNA, thymine is replaced by uracil and the sugar is ribose.
It is possible to simplistically think about these genetic codes as the information storage books of life. The chapters of these books are the genes. All living things on this planet (from bacteria to plants, to humans) use the same genetic material, the same four letters based code.
It is therefore not hard to imagine how the study of these codes deeply fascinates scientists. Understanding their structure and function, not only allows for a deeper understanding of life, but it can also bring to important discoveries with practical applicability.
In this post, I would like to expand on the first purpose, probably more academically oriented, but so incredibly charming.
One of the characteristics of DNA and RNA is their ability to store and propagate information. The colour of my hair, my eyes or my skin are genetic traits. This sort of information is stored in the form of genetic material (DNA) in our genes, and it is passed over from one generation to another. This is an example of the most evident and macroscopic effect of genetic information transfer, but it is just a consequence of information transfer at a molecular level.
In a recent paper, Dr. Pinheiro and colleagues proved that it is possible to store and recover genetic information from 6 alternative synthetic genetic molecules. These polymers (just another way to call long sequences of repeating units such as our four letters) are referred to as xeno nucleic acids (XNAs). XNAs are very similar to DNA or RNA but carry small modifications in the sugar part of the molecule and are not present in nature.
XNAs demonstrated to be capable of heredity (passing down of their genetic information) and also and foremost of evolution, features that were believed to be prerogatives of DNA and RNA.
It is therefore now conceivable that heredity and evolution themselves are likely to emerge in other polymers providing that they are capable of information storage.
The discovery of this “synthetic DNA” opens a whole new chapter in the study of Darwinian evolution. It is long believed that DNA might not be the very first genetic material existed on earth. The proof that polymers other than DNA are capable of similar behaviour corroborates the hypothesis of the existence of a different (maybe simpler) genetic material pre-dating DNA. These molecules have the potential to bring us closer to solve the mystery of the origin of life.
Biological systems are nothing but very complex machines able to recognise and work with DNA and RNA as their genetic material. If we could re-engineer our natural machinery to recognise XNA instead, we would be one step closer to the creation of an exotic (and completely synthetic) form of life. There are teams of scientists (such as the lab of Dr. Romesberg at the Scripps Institute in California) already working on this and they are getting every day a step closer.
Xenobiology is the name given to this branch of science. It is indeed very exciting, and I cannot wait to hear about future discoveries and applications involving XNA!
Pinheiro, V. B. et al. Synthetic genetic polymers capable of heredity and evolution. Science 336, 341–344 (2012)
Malyshev, D. A. et al. A semi-synthetic organism with an expanded genetic alphabet. Nature 509, 385–388 (2014)