Salts, Heat Flows May Have Led To Self-Replicating Biomolecules

A study conducted by German scientists has shown that a blend of salts in the presence of heat flows may have contributed to the formation of the first self-replicating biomolecules and jumpstarted the origin of life on earth, Science Daily reported.

Photo Insert: Ludwig-Maximilians-Universität München (LMU)

According to the "RNA world" hypothesis, primordial living systems were based on self-replicating RNA molecules. Chemically speaking, RNA is closely related to DNA. However, in addition to storing information, RNA can fold into complex structures that have catalytic activity, similar to the protein nanomachines that catalyze chemical reactions in cells.

RNA is of particular interest in the context of the origin of life as a promising candidate for the first functional biopolymer, the Ludwig-Maximilians-Universität München (LMU) in Munich said.

To fold correctly, RNA requires a relatively high concentration of doubly charged magnesium ions and a minimal concentration of singly charged sodium, since the latter leads to misfolding of RNA strands. Drying alone alters the salt concentration, but not the relative amounts of the different ions.

LMU biophysicists Dieter Braun and Christof Mast, in collaboration with colleagues at the Max Planck Institute for Biochemistry, the Technical University (TU) in Dortmund and LMU Geosciences, have asked how the relevant salt balance might have been achieved under the conditions that prevailed on Earth some 4 billion years ago.

LMU geoscientists led by Donald Dingwell and Bettina Scheu first synthesized basaltic glass, and characterized the basalt in its various forms, as both rock and glass. Basaltic glass is produced when melted basalt is rapidly cooled, e.g. when it comes into contact with ocean water -- a natural process that occurs continuously,

They found significantly more sodium than magnesium in the water, and the latter was present in much lower concentrations than those required by the prebiotic RNA nanomachines.

"However, this situation changed considerably when heat currents -- which are very likely to have been present, owing to the high levels of geological activity expected in prebiotic environments -- were added," says Mast.

In the narrow pores and cracks that are a feature of basaltic glasses, temperature gradients not only induce convective flows, they also result in the net movement of ions against the direction of the current.

The magnitude of this effect, which is known as thermophoresis, is strongly dependent on the size and electrical charge of the ions concerned. This combination of convection and thermophoresis eventually results in the local accumulation of magnesium ions in much higher local concentrations than sodium ions. The team confirmed that ligation of RNA strands and ribozyme self-replication are more efficient under thermophoretic conditions.

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