Life may have originated at bottom of sea, suggests new study
A lab reconstruction of Earth's "ancient ocean" has suggested that how the first organisms on the planet could have become metabolically active at the bottom of the sea.
The results of the research, conducted at the University of Cambridge, permit scientists to speculate how primitive cells learned to synthesize their organic components - the molecules that form RNA, lipids and amino acids.
A reconstruction revealed the spontaneous occurrence of the chemical reactions used by modern cells to synthesize many of the crucial organic molecules of metabolism.
Previously, it was assumed that these reactions were carried out in modern cells by metabolic enzymes, highly complex molecular machines that came into existence during the evolution of modern organisms.
An open question for scientists is when and how cellular metabolism, the network of chemical reactions necessary to produce nucleic acids, amino acids and lipids, the building blocks of life, appeared on the scene.
The observed chemical reactions occurred in the absence of enzymes but were made possible by the chemical molecules found in the Archean sea.
Finding a series of reactions that resembles the "core of cellular metabolism" suggests that metabolism predates the origin of life.
This implies that, at least initially, metabolism may not have been shaped by evolution but by molecules like RNA formed through the chemical conditions that prevailed in the earliest oceans.
Dr. Markus Ralser, from the Depart. of Biochemistry at the university, said that the results demonstrate that the conditions and molecules found in 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.
In the 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, he said.
From the analysis of early oceanic sediments, geoscientists and co-author of the study, Alexandra V. Turchyn, from the Department of Earth Sciences at the university, concluded that soluble forms of iron were one of the most frequently found molecules in the prebiotic oceans.
The scientists reconstructed the conditions of this prebiotic sea based on the composition of various early sediments described in the scientific literature.
Ralser said that in the presence of iron and other compounds found in the oceanic sediments, 29 metabolic-like chemical reactions were observed, including those that produce some of the essential chemicals of metabolism, for example precursors of the building blocks of proteins or RNA.
These results indicate that the basic architecture of the modern metabolic network could have originated from the chemical and physical constraints that existed on the prebiotic Earth, he said.
The detection of one of the metabolites, ribose 5-phosphate, in the reaction mixtures is particularly noteworthy as its availability means that RNA precursors could in theory give rise to RNA molecules that encode information, catalyze chemical reactions and replicate.
The study has been published in the journal Molecular Systems Biology.
(Posted on 27-04-2014)