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The potassium world

Life was born in the sea, and even the organisms that invaded the land could do so only by carrying with them an internal sea that enabled their cells to continue to live in water. This liquid that floods every cell still has values of pH and osmotic pressure which are similar to those of sea water, and likewise contains high concentrations of sodium and potassium ions. The really extraordinary thing, however, is that inside all cells (including those that live in the sea) the concentrations of sodium and potassium are totally different from those of the surrounding liquid. [Pg.164]

A first explanation of this strange experimental fact came into view when it was found that sodium ions (Na+) produce very high osmotic pressures inside the cell, and, without defence mechanisms, a cell would swell to bursting point and nothing could save it. The osmotic defence mechanisms can be of three kinds (1) an external wall that prevents swelling from the outside, (2) an internal web of filaments that ties the cell membrane from the inside, or (3) a battery of ion pumps on the cell membrane which contually drains out the excess sodium. [Pg.164]

The first clue was provided by Martin Lubin (1964) and by Cahn and Lubin (1978), with the discovery, first in bacteria and then in eukaryotes, that protein synthesis comes to a halt if high concentrations of potassium ions are not present. As a matter of fact, potassium is [Pg.164]

At this point, however, we cannot ignore the fact that the evolution of protein synthesis started before the origin of the first cells, in systems which could not have cell walls, cytoskeleton filaments or sodium pumps, for the very good reason that all these structures require well-developed proteins. How could precellular systems have high potassium concentrations, and low sodium levels, without any of the molecular mechanisms that cells employ to this end The most plausible answer is that those concentrations did not have to be produced in prebiotic systems because they already existed in the environment of the primitive seas. The ribotype world, in short, was also a potassium world. [Pg.165]

It is not possible, of course, to rule out other explanations, but none has the simplicity and the explicative power of this direct environmental hypothesis. And we cannot exclude the possibility of an experimental test it would be enough to discover in the geological record the signs of ancient seas where potassium was more abundant than sodium (such a discovery would allow us, among other things, to put a date on the origin of life). [Pg.165]


The potassium world hypothesis does not seem to have a clear paternity. It was circulating in the 1970s at informal meetings on the ionic conditions of protein synthesis, but I have been unable to trace it to a precise source. Today it is less popular, but it is mentioned here... [Pg.165]


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