|Electron microscope image of a liposome - a circular membrane automatically formed by the simple act of dropping a fatty lipid into water. Image: NOC Corporation, 2014.|
Organic molecules in modern living cells aren't capable of doing much by themselves, but the simple act of adding lipids to water automatically forms circular fatty droplets - which function as primitive cell membranes - and the organic chemicals trapped within can react in amazing ways, automatically organizing themselves into functioning biological factories.
Dr. Pasquale Stano and a research team at the University of Roma Tre use this approach to study how life may have first emerged. In a 2014 experiment, they selected a simple assembly of 83 different molecules which produce proteins. Among these was a string of DNA programmed to synthesize a green fluorescent protein (GFP) that could be seen under a microscope.
Living cells tend to be tightly packed, dense with molecular machines; this is because such assemblies can only function (i.e. produce proteins) when their molecules are in close enough proximity to react with one another. Dilute the assemblies with water, and they can no longer function.
To artificially bring about the necessary molecular density, Dr. Stano's team added a fatty molecule called POPC to the mixture. Because it doesn't mix with water, POPC automatically forms a bubble-like enclosure called a liposome, similar in structure to a living cell membrane. Such tiny naturally-occurring formations are used widely in research into the origins of life.
In Dr. Stano's experiments, some of the assembly molecules were randomly trapped within the liposomes. Among them, five out of every 1,000 liposomes contained all 83 of the molecules necessary to synthesize a protein, which they did in large amounts, until the solution began to glow green under a microscope. According to computer calculations, this is impossible. In fact, the chance of even a single liposome containing just the right combination of all 83 necessary molecules is virtually zero. The fact that they formed correctly in such great numbers to produce the target protein is indicative of an astounding possibility: that the self-assembly of molecular machines into simple cells may be an inevitable process of nature.
Source: "Chemists show life on Earth was not a fluke", October 24, 2013, The Conversation, Andrew Bissette, University of Oxford
This is an excerpt from the upcoming revised edition of The Path Book I: Origins.