As much as we have learned about the way natural selection can produce ever more complex species from the simplest self replicating units, big questions remain. Particularly significant is the question of how the organic compounds that make up RNA could have emerged from the oceans of the early Earth.
Our bodies, and those of other living things, use metabolic enzymes to cut and paste elements and compounds to produce the crucial letters out of which the book of life is written. These enzymes are in turn produced by RNA. However, this creates the original chicken and egg problem – where did the RNA come from, given its own complexity?
However, a Cambridge University team have revealed in Molecular Systems Biology that these same reactions can also be triggered by the chemicals believed to have existed in the Archean sea that existed 4-2.5 billion years ago.
“Our results demonstrate that the conditions and molecules found in the Earth’s ancient oceans assisted and accelerated the interconversion of metabolites that in modern organisms make up glycolysis and the pentose-phosphate pathways, two of the essential and most centrally placed reaction cascades of metabolism,” says Dr Markus Ralser, who heads the team that made the discovery.
“In our reconstructed version of the ancient Archean ocean, these metabolic reactions were particularly sensitive to the presence of ferrous iron that helped catalyze many of the chemical reactions that we observed,” Ralser continues. While in many contexts the word ferrous means all iron, in chemistry it refers to iron compounds with an oxidation number of 2+. Geoscientists contributing to the research concluded from studies of the earliest sediments that ferrous iron was common in the oceans before photosynthesis introduced free oxygen to the air and water.
The discovery came about when Ralser asked one of his students to do quality control of the medium their lab used to culture cells. The student ran some of the medium through a mass spectrometer as a short cut and picked up signs of pyruvate (CH3COCOO−), a base that is key to essential metabolic pathways. As its chemical formula suggests pyruvate is not a simple compound, so it was surprising to find it appearing without the enzymes that within cells produce it from glucose. The glycolysis pathway is a ten step process, each requiring enzyme catalysis.
Ralser's team repeated the experiments to see how the pyruvate got there and found metals were standing in for the enzymes as catalysts. "People have said that these pathways look so complex they couldn't form by environmental chemistry alone," Ralser told New Scientist. “This is the first experiment showing that it is possible to create metabolic networks in the absence of RNA."
Thanks to for the find!
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