[A]fter a decade of careful , it looks as if all known eukaryotic cells either have or once had... mitochondria. - Nick Lane

It could be any of those [sodium, or other ion gradients]. The fact of life on earth is that it tends to use proton gradients, and we know particular environments that do use proton gradients, and the reason I think protons is because , which is to say the proton concentration, can modulate the reactivity of both and . Now sodium concentrations wouldn't do that, but protons, if you've got gas in alkaline fluids, hydrothermal fluids... what you've got coming out of these s, hydrogen is more reactive in alkaline conditions. It really doesn't want to push its electrons onto something else, but if it's in alkaline conditions it pushes its electrons onto something else, and the protons are left behind and they will react immediately with the hydroxide ions to form water, which is thermodynamically very favored, and so it's far more likely to push its electrons onto CO₂ if it's in alkaline solution.

In bacteria, the DNA forms into a long and twisted loop. The contorted tracks... close... to form a singular circular . In eukaryotic cells, there are usually a number of different chromosomes... each has two separate ends.

It is the movement that creates the form.