Did Early DNA Replicate at the Bottom of the Sea?

31753dna_screen05 Lab experiments reveal that the precursor of life may have learned how to copy itself thanks to simple convection at the bottom of the ocean in tiny pores around undersea hydrothermal vents where magnesium-rich rocks react with sea water, creating a heat source that could drive miniature convection currents in nearby pores in the rock, according to research by Christof Mast and Dieter Braun of Ludwig Maximilian University of Munich, Germany, who proposed that such convection could concentrate nucleotides, strands of DNA, and polymerase, providing a setting that would promote replication. 

Sea water inside pores on or near a vent's chimney may undergo thermal convection because the water at the wall of the pore closest to the vent's heat source would be warmer than the water near the furthermost wall, said Mast and Braun. If the pore contained strands of DNA, nucleotides, and polymerase they would ride upward in the warm current. The DNA strands would also be "unzipped" in the heat, splitting into two strands that each serve as templates for eventual replication. These components would then tend to shift away from the rising warmer region. In air, particles typically shift into a colder current because they are more likely to be pushed away by warmer, more energetic molecules than those on the cooler, calmer side. The researchers reckon a similar process would occur in the fluid in the vents.

Over time, the DNA templates, polymerase and nucleotides would collect at the bottom of a pore. Once there, they could become concentrated enough for the polymerase to bind new nucleotides to the single-strand DNA templates, replicating the original DNA.

To test this theory, Mast and Braun put these ingredients into tubes 1.5 millimetres long. They used a laser to heat one side of the water and create thermal convection. Sure enough, they found that the DNA doubled every 50 seconds (Physical Review Letters, vol 104, p 188102).

Fatty acids in the water may have provided a shuttle service, says Braun allowing replicated DNA to move between pores to recombine with new templates, producing a variety of configurations. Last year, a team at Harvard University found that fatty acids driven by convection will form membranes that could trap the concentrated genetic material and transport it.

Casey Kazan via New Scientist

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