UCL (UK) — Scientists say the chemistry of deep-sea hydrothermal vents may explain how the first living cells developed.
At the origin of life, the first protocells must have needed a vast amount of energy to drive their metabolism and replication, as enzymes that catalyze very specific reactions were yet to evolve.
So where did all that energy come from on the early Earth, and how did it get focused into driving the organic chemistry required for life?
Nick Lane at the University College London and Bill Martin at the University of Dusseldorf address those questions—and why all life as we know it conserves energy in the peculiar form of ion gradients across membranes—in their research published in the journal Cell.
“Life is, in effect, a side-reaction of an energy-harnessing reaction. Living organisms require vast amounts of energy to go on living,” 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.”
Humans consume more than a kilogram (more than 700 liters) 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 by mass as much waste product from their respiration as organic carbon.
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 genetic code 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 energy metabolism 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-sulphur mineral walls, could have driven the assimilation of organic carbon, giving rise to protocells within the microporous labyrinth of these vents.
They go on to demonstrate that such protocells 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.
Source: University College London