The question of what 'life' means is open to argument, but Dr Liu believes that four crucial systems, working together, make up what we know today as 'life'. These four systems are membranes, nucleic acids, proteins and metabolism. "What we are thinking is that if modern life needs these four systems together, prebiotic chemistry should also have a synergic system including all four systems at the same time."
Dr Liu explains what he means by a synergic system. "Imagine there is a car on a hill, but there is no brake fluid in the car – it rolls downhill spontaneously. Now imagine that the car has a special braking system, whereby it uses the fuel waste as brake fluid. This means that after the car is driven up the hill, consuming fuel, it can remain there thanks to the useful fuel waste."
In their paper the group has looked at a prebiotic synergic system – the conversion of phosphate to cyclic phosphate. The reaction uses copper cations (Cu2+) as a catalyst. However the copper cations also catalyse the conversion of cyclic phosphate back to phosphate. To stop this from happening, a second molecule, a nitrile, is added. During the reaction, the copper cation converts the nitrile to an amino acid. The amino acid – effectively the waste-product of the reaction – then inhibits the cyclic phosphate from converting back to a phosphate.
To use the car analogy, the copper cation is the engine, the nitrile is the fuel, and the amino acid is the fuel waste, which also doubles as braking fluid.
"We have reused the byproduct of the activating system and established a protecting system in situ", says Dr Liu.
The two systems of copper–nitrile and copper–amino acid reinforce each other and work together to make the reaction go forward. This is the sort of reaction that Dr Liu’s group believes must have existed in the transition period from prebiotic chemistry to biology. They hope to develop further synergic systems that could eventually give us clues as to the origins of life.
This article is free to read in our open access, flagship journal Chemical Science: Ziwei Liu et al., Chem. Sci., 2018, Accepted Manuscript. DOI: 10.1039/C8SC002513D. You can access all of our ChemSci Picks in this article collection. Read more like this