Origin of Life Emerged from Cell Membrane Bioenergetics
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
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 catalyse very specific reactions were yet to evolve. Most energy flux must have simply dissipated without use.
The work is published in Cell this last week of December 2012.
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?
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. Living organisms 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 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-sulfur 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).
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."
The study was funded by a UCL Provost's Venture Research Fellowship, the Leverhulme Trust and the European Research Council.
About UCL (University College London)
Founded in 1826, UCL was the first English university established after Oxford and Cambridge, the first to admit students regardless of race, class, religion or gender and the first to provide systematic teaching of law, architecture and medicine.
We are among the world's top universities, as reflected by our performance in a range of international rankings and tables. According to the Thomson Scientific Citation Index, UCL is the second most highly cited European university and the 15th most highly cited in the world.
UCL has nearly 25,000 students from 150 countries and more than 9,000 employees, of whom one third are from outside the UK. The university is based in Bloomsbury in the heart of London, but also has two international campuses UCL Australia and UCL Qatar. Our annual income is more than £800 million.
Original article: http://www.eurekalert.org/pub_releases/2012-12/ucl-ool121912.php