The very basis of life can now be created in the laboratory and it’s not unique. What more this artificial genetic material can mingle easily with the real thing, even evolving as the real thing does. The creation of artificial DNA and RNA strands have been reported by Pinheiro et al. They have even observed their evolution.
A new class of molecules, very similar, but not quite
Till now, the only molecules known to be capable of undergoing Darwinian evolution were RNA and DNA, but this discovery suggests that there might be a lot more candidates that fit the bill. There is really no “Goldilocks solution”.
DNA (or RNA) has a double helical structure, meaning that it looks like two strips of paper wound around each other in a helical fashion. The structure is ladder like – with each rung consisting of two nucleotide bases held together by sugar molecules.
Pinheiro’s group retained the nucleotides of DNA – the Adenine, Guanine, Cytosine and Thymine (or Uracil, in case of RNA) – but altered the sugars that bind these nucleotides together. In this way, he created XNA, with the ‘X’ standing for the sugar used. DNA, or deoxyribonucleic acid, uses deoxyribose as the sugar, while RNA, or ribonucleic acid, uses ribose as the sugar. But these use different sugars, thus giving them different names. For example, arabinose is the sugar in ANA, flourarabinose in FANA, threose in TNA, a “locked” ribose in LNA and a cyclohexane in CeNA.
Retention and copying of information
Here is the crucial bit: Even though the sugar bases were changed, the nucleobases being the same meant that these artificial XNA’s behaved exactly like the DNA found naturally. They could even pair up with the naturally found DNA.
Here is another crucial bit of the story: When DNA or RNA create copies of themselves, they use helper molecules called polymerases. These polymerases separate the two chains of the double helix structure, read the sequence of letters, helps in the formation of a similar chain, zips the whole thing back again and creates a new DNA molecule, all in this process called transcription. Evolution – or small genetic changes in the DNA structure – happens the copy of the DNA is not exactly like its parent. Environmental factors then ‘selects’ the more competitive versions of these modified DNA molecules and this helps them create more copies of themselves. Thus, a trait is acquired and another is lost.
Building your own genetic copy machines
The team had to build separate polymerase molecules to help transcribe the XNA’s. They were able to, thus, transcribe the code of the synthetic DNA to natural DNA and then back to the synthetic DNA. The XNA’s thus formed are just as immune or vulnerable to the original DNA. XNA’s must also be able to proliferate just like DNA does without any external help, in a process called amplification. Amplification was noticed with the artificial polymerases and the XNA’s. This is important, otherwise the XNA’s won’t be able to undergo Darwinian evolution like DNA.
In one of the experiments, a control was set up. The factors were controlled such that if the XNA did not ‘cling on’ to a particular protein, it would be washed away. Pretty soon more and more XNAs began developing this trait. This again proves that the two very important traits of inheritance through genetics and selection – information storage with high fidelity of copying and propagation of mutations – are not characteristics of just DNA or RNA. This gives the grand possibility of finding a whole new structure of biochemistry.
Maybe novel forms of life are not that far away in the future!