The second problem is the membrane itself. Even putting aside the question of what type of membrane it was, there is again the issue of disturbing early sophistication. In modern cells, chemiosmotic coupling only works if the membrane is almost impermeable to protons. But all experiments with plausible early membranes suggest that they would have been highly permeable to protons. It’s extremely difficult to keep them out. The problem is that chemiosmotic coupling looks to be useless until a number of sophisticated proteins have been embedded in a proton-tight membrane; and then, but only then,
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