Origin of life emerged from cell membrane bioenergetics

Dec 20, 2012

A coherent pathway which starts from no more than rocks, water and carbon dioxide and leads to the emergence of the strange bio-energetic properties of living cells, has been traced for the first time in a major hypothesis paper in Cell this week.

At the the first protocells must have needed a vast amount of energy to drive their metabolism and replication, as enzymes that catalyse very specific reactions were yet to evolve. Most energy flux must have simply dissipated without use.

So where did it all that energy come from on the , and how did it get focused into driving the required for life?

The answer lies in the chemistry of deep-sea hydrothermal vents. In their paper Nick Lane (UCL, Genetics, Evolution and Environment) and Bill Martin (University of Dusseldorf) address the question of where all this energy came from - and why all life as we know it conserves energy in the peculiar form of ion gradients across membranes.

"Life is, in effect, a side-reaction of an energy-harnessing reaction. require vast amounts of energy to go on living," said Nick Lane.

Humans consume more than a kilogram (more than 700 litres) of oxygen every day, exhaling it as carbon dioxide. The simplest cells, growing from the reaction of hydrogen with carbon dioxide, produce about 40 times as much waste product from their respiration as organic carbon (by mass). In all these cases, the energy derived from respiration is stored in the form of ion gradients over membranes.

This strange trait is as universal to life as the itself. Lane and Martin show that bacteria capable of growing on no more than hydrogen and carbon dioxide are remarkably similar in the details of their carbon and to the far-from-equilibrium chemistry occurring in a particular type of deep-sea hydrothermal vent, known as alkaline hydrothermal vents.

Based on measured values, they calculate that natural proton gradients, acting across thin semi-conducting iron-sulfur mineral walls, could have driven the assimilation of , giving rise to protocells within the microporous labyrinth of these vents.

They go on to demonstrate that such are limited by their own permeability, which ultimately forced them to transduce natural proton gradients into biochemical sodium gradients, at no net energetic cost, using a simple Na+/H+ transporter. Their hypothesis predicts a core set of proteins required for early energy conservation, and explains the puzzling promiscuity of respiratory proteins for both protons and sodium ions.

These considerations could also explain the deep divergence between bacteria and archaea (single celled microorganisms) . For the first time, says Lane, "It is possible to trace a coherent pathway leading from no more than rocks, water and carbon dioxide to the strange bioenergetic properties of all cells living today."

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More information: 'The Origin of Membrane Bioenergeticsis' published in the journal Cell on 21st December.

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VendicarD
2.3 / 5 (3) Dec 20, 2012
pllllllllllp

MrVibrating
5 / 5 (1) Dec 20, 2012
This is a truly fascinating new angle on life's genesis, focusing as it does on raw thermodynamics over questions of genetics that might otherwise seem intractable. Nick Lane has been developing this idea for some time, recently summarising it in a very well written (and received) New Scientist article... highly recommended reading:

http://www.nick-l...Life.pdf

And previously (Lane & Martin):

http://www.newsci...nce.html
Torbjorn_Larsson_OM
2 / 5 (1) Dec 20, 2012
This is a good pathway for hydrothermal vent organics, I'm sure.

But as an overall theory for emergence it now has to compete with the recent thermodynamic models that a) has a TD force, so can't stall as other pathways and b) yields RNA uniquely as original replicator from first principles. ["Thermodynamic Basis for the Emergence of Genomes", Woo et al, PLOS Comp Biol 2012. There is also a similar paper tbp on how RNA is the currently only known heteromer that can make replicators to start off evolution.]

And honestly, I've never understood the obsession with tying archaea and bacterial divergence to early evolution. Protein fold and lipid membrane metabolism phylogenies rejects that flatly and predicts a later lipid chirality split from an ancestral whatever-works membrane.

I admire the predictivity and simplicity of Lane's energy theory on eukaryotes as much as I like Valentine's on archaea. For the same reason I don't like this line of work, which is non-predictive and complex.
Tausch
1 / 5 (1) Dec 21, 2012
"Life is, in effect, a side-reaction of an energy-harnessing reaction." - Lane


Perhaps these researchers can profit from a new proposal for life:
http://phys.org/n...ife.html

Perhaps a more basic sequence to commence with energy distribution considerations of a system in terms of information is more complete to define the fundamental question of what we label life.

RealScience
not rated yet Dec 21, 2012
Life is that which has evolved to evolve.
Excludes fire, crystals, etc.

Includes languages as a borderline case, and languages do have many information-carrying properties in common with the RNA/Protein/DNA based life we refer to as 'life-as-we-know-it.