The Origin of Life, Part III: Primitive Cells
The experiments of Miller, Fox, Ferris and others had shown that complex polymers could arise spontaneously on the early Earth. We know, however, that the organic molecules that make us up are not just a jumble of things floating around in a primordial soup, they are highly ordered. They come in highly ordered packages. There are many such packages in living systems, but the most fundamental one is what we call the cell. All living things are made of units called cells. Minimally, for something to be living, requires a barrier between the living part and the non-living part. That barrier is what would define the cell.
Is it possible that some cell-like structure could arise spontaneously on the early Earth? Here, too, laboratory experiments suggest that the answer is yes. A number of experiments have been done that demonstrate, under conditions that are not too rigorous, that you can get aggregations of molecules that would spontaneously form cell-like structures.
This kind of spontaneously made cells are called protobionts. You can actually make protobionts, it is not difficult to do. You can make them under a number of different kinds of conditions. For example, if you have the right kind of lipids, you can almost literally put them in water and they spontaneously form a package where there is a membrane of lipids that encloses some central space.
The most remarkable kind of protobiont, called coacervate, is one that has been made to self-assemble out of a solution that includes polypeptides, nucleic acids and polysaccharides. If you have the right conditions, you can make these to self-assemble into a cell-like object. What is really interesting about coacervates is that if you then throw into the mix some real biological molecules, a protein enzyme that you’ve taken from a real living cell, for example, the coacervates can take up those enzymes. They would bring them inside of themselves.
Those enzymes would start working inside the coacervates. What enzymes do is to process some kind of biological molecule into another. Once these enzymes have been taken up by these coacervates, it would also start doing the reactions and putting out the products. This is really getting remarkably close to something that we might want to call living.
I don’t say that we can make primitive cells. Nobody has actually made a cell that any biologist would look and say “oh, that’s a cell you just made”. People are trying to do that now, but it hasn’t been done yet. We can, however, make cell-like things and it doesn’t seem to be any big trick. These things spontaneously form, we know that for sure.
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