Chemists show how life on Earth may have started

University of Utah

Though we have not determined which chemicals existed on prebiotic Earth, studying the biomolecules we have today aids our understanding of how life could have started 3 billion years ago. Biomolecules are essentially biogenic substances, molecules that are produced by living organisms. Scientists used a set of biomolecules to show how life may have started. These molecular machines do not do much on their own, but when fatty chemicals are added to act as a primitive version of a cell membrane the chemicals got close enough to react in a specific manner.

Figuring out this form of self-organisation may be the key to understanding how life formed on Earth and how it may form on other planets. Self-organisation is where different chemicals come together because of the forces acting on them, and become a molecular machine which is capable of even more complex tasks. Every living cell is full of molecular machines.

A team of researchers at the University of Roma Tre wanted to use this knowledge to investigate the origins of life and chose an assembly that produces proteins. The assembly contained 83 different molecules including DNA, which was programmed to produce a special green fluorescent protein (GFP) observable under a confocal microscope. The assembly only produced proteins when its molecules are close enough together to react with each other, and the assembly can no longer react when it is dilutes with water.

The lead researcher, Stano, then added a chemical called POPC to the dilute solution. POPC is a fatty molecule and does not mix with water; fatty molecules form liposomes when placed in water. They have a similar structure to the membranes of living cells. Stano found that many of the liposomes trapped some of the molecules in the assembly, though five in every 1,000 liposomes had all 83 of the molecules needed to produce a protein. Those liposomes produced a large amount of GFP and glowed under a microscope.

Calculated probability revealed that five liposomes in 1,000 could not have trapped all 83 molecules in the assembly. The probability for one liposome to form is essentially zero, indicating that the formation of any liposomes and GFP produced was truly remarkable.

The next step for Stano and his colleagues is to determine if similar but less complex molecules can also achieve this accomplishment. At the very least, this work shows that self-assembly into simple cells may be an inevitable physical process.

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