How life originated from an inanimate set of chemicals is still a mystery. While we may never be certain about precisely which chemicals existed on prebiotic Earth, we can study the biomolecules we have today to give us clues about what happened three billion years ago.

Now, scientists have used a set of modern biomolecules to show that the formation of larger, more complex groupings of molecules may be inherently favored. They found that when components of the molecular machines that exist in living cells today are mixed with membrane material, functional complexes form more often than you’d expect from chance.

As of now, we don’t know how this form of self-organization takes place. Figuring it out may help us understand life’s origins on Earth and perhaps how it might form on other planets.

The 1987 Nobel Prize in Chemistry was given to chemists for building complex molecules that could bind very specifically to other atoms and chemicals. In the right combinations, these molecules can self-organize, forming a molecular complex that can be capable of even more complicated tasks. Each living cell is full of molecular machines, formed, in part, by their ability to self-organize.

Pasquale Stano at the University of Roma Tre and his colleagues were interested in using this knowledge to probe the origins of life. To make things simple, they chose an assembly that produces proteins. This assembly consists of 83 different molecules, including an RNA that encoded a special green fluorescent protein (GFP) that could be used to identify places where complexes formed successfully.

The assembly can only produce proteins when all of its molecules are close enough together to interact with each other. When the assembly is diluted with water, no GFP gets made. (This is one reason that the insides of living cells are very crowded: it allows the chemistry of life to work.)

In order to recreate this molecular crowding, Stano added a chemical called POPC to the dilute solution. Fatty molecules such as POPC do not mix with water, and when placed into water they spontaneously form small, spherical bodies called liposomes. Liposomes have a very similar structure to the membranes of living cells and are widely used to study the evolution of cells.

Stano reports in the journal Angewandte Chemie that many of these liposomes trapped some of the other molecules present in the mixture. But remarkably, five in every 1,000 of them had all 83 of the molecules needed to produce a protein. These liposomes ended up filled with GFP and glowed green under a microscope.

Computer calculations reveal that, by chance, five liposomes in 1,000 could not have trapped all 83 molecules of the assembly—they calculated the possibility of forming even one such liposome essentially zero. The fact that any GFP was produced means something quite unexpected is happening.

Stano and his colleagues do not yet understand why the formation of complexes was favored. It may be that these particular molecules are suited to this kind of self-organization because they are already highly evolved to interact. An important next step is to see if similar, but less complex, molecules are also capable of this feat.

Regardless of the limitations, Stano's experiment has shown for the first time that self-assembly into simple cells may be an inevitable physical process. Finding out how exactly this self-assembly happens could mean taking a big step towards understanding how life was formed.

Angewandte Chemie, 2013. DOI: 10.1002/anie.201306613 (About DOIs).

Andrew Bissette is a PhD student at Oxford University. The article was first published on The Conversation.