60 years of silence - so far

[bilby]

Supreme wisdom and kn wedge?

I don't know about supreme wisdom, but Wedge can certainly fly an X-Wing pretty well.



Didn't know his first name was Ken, either.

 

[Swammerdami]

So we go from an organism that exploited a proton gradient in its environment to one that created its own proton gradient by pumping protons out of its interior.

It's good to see another Nick Lane fan here! He makes an interesting deduction about the transition from the early proto-life (including LUCA) -- which use a natural proton gradient as an energy source -- to the earliest cells which produced their own energy, e.g by methanogenesis.

Early life did not need an impermeable membrane (it got all the protonic energy it needed for free) and in fact needed a permeable membrane: the opposite membrane needed to excrete protons (or ingest hydroxyl) or the cell would soon acquire excess charge. But once cells developed their own proton-pumping for their own energy metabolism, an impermeable membrane was a necessity: No sense spending energy pumping protons out if they're just going to rush back in uselessly.

This created a chicken-or-egg problem. If exploiting natural proton flux REQUIRES permeable membranes but self-produced energy REQUIRES very IMpermeable membranes, how can we evolve from the former to the latter?

Enter the sodium–hydrogen antiporter to the rescue! This transmembrane protein exchanges hydrogen ions for sodium ions (or vice versa). Sodium ions are just as useful as hydrogen ions (or actually hydronium ions) as inputs to chemiosmosis channels (e.g. ATP synthase) but, being larger than protons, do not "waste" their energy as easily by bypassing those channels. Replacing hydrogen with sodium meant that these early cells could tolerate a broader range of membrane permeability. (The anti-porter required little energy to operate since its exchange is electrically neutral.)

Impermeable membranes were apparently finalized after LUCA spun off proto-bacteria and proto-archaea separately. Differences in the two membrane structures leads to this conclusion.

The genetic code, its associated ribozymes and enzymes, the magnificent ribosome machine, metabolic enzymes like ferredoxins and ATP synthase, and even RNA-DNA reverse transcriptase -- these were all essential to the earliest life before free-floating cells could develop. But according to Nick Lane, sodium–hydrogen antiporters were also necessary.