Wednesday, January 28, 2015
The Crucible of Life
Micropore systems in hardened rock, filled with water and heated by volcanic activity, can function as incubators for RNA and DNA synthesis. Here, precursor molecules are highly concentrated in water; the conditions are perfect for combining comparatively simple biomolecules into polymers capable of self-reproduction and the stable storage of genetic information.
Temperature differences within these pore systems create inductive cycles which naturally drive the replication of these nucleic acids. If heat is localized to one side of an elongated pore, biomolecules washed into the pore and trapped within will be concentrated by the temperature gradient. This is because of thermophoresis: ionically-charged molecules are compelled to move from warmer to cooler regions; this concentrates the most complex polymers, like RNA and DNA, in the cooler end of the pores.
Dr. Dieter Braun and colleagues at Ludwig-Maximilians-Universitaet in Munich have demonstrated this natural process in the laboratory, using tiny glass capillary tubes in place of natural volcanic rock pores. Heating one end of the glass tubes and allowing water containing DNA of varying lengths to percolate through creates a concentration of the longest, most complex molecules at one end.
Porous, heated igneous (volcanic) rocks - were common on early Earth, which experienced much more intense, widespread volcanic activity. Trace metals within these rocks enhance the induction process, conducting heat with 100 times the efficiency of water.
Within the hotter region, double strands separate into single component strands in minutes. These concentrated, single-strand and ionically-charged nucleic acids are transported by convection (suction) back into the colder region, where they encounter DNA building blocks - nucleotides - which are continuously fed into the pore. The single strands can then act as templates, polymerizing complementary strands, thus allowing both replication and elongation - by stitching fragments together.
When nucleic acids are concentrated beyond the pore's storage capacity, the newly replicated molecules are spewed out into the cooler surrounding water, where they can colonize neighboring pore systems.
These real-world conditions create an autonomous, continuous system - a Darwinian evolution of organic molecules with ever-greater complexity, in which life is able to evolve from simple chemical precursors.
As mentioned in a previous story, we now know that life is believed to be inevitable, driven by the chemical need to reach stability by shedding energy, "...fundamentally a thermodynamic non-equilibrium phenomenon," says Dr. Braun. "That is why the emergence of the first life-forms requires a local imbalance driven by an external energy source -- for example, by a temperature difference imposed from outside the system."
That this can be achieved in such a simple and elegant way was surprising even to us," he added.
Source: "Labyrinths as crucibles of life", press release, Ludwig-Maximilians-Universitaet, January 27, 2015