Image above: Are metabolic pathways the result of the evolutionary selection of enzymes — and thus did they appear as a consequence of genetics that were possible in the RNA world (top row)? Or does metabolism date back to chemical reaction sequences based on a prebiotic chemistry, which then facilitated the emergence of RNA components and, therefore, of genetics (bottom row)? Photo courtesy of Molecular Systems Biology
Researchers recreated the chemical mixture of Earth’s warmer early oceans and observed chemical reactions similar to those that take place within living cells.
The new study suggests the process of metabolism that organic cells use to grow, change and multiply might have existed before life itself.
Before about 4 billion years ago, the Earth was a very different place; devoid of oxygen and life, the planet’s oceans were hot and rich with iron. From those oceans arose the first life forms. But how exactly the steps toward the origins of life took place, and in what order, remains unknown.
CIFAR Fellow Alexandra Turchyn (University of Cambridge) and two collaborators conducted an experiment using a recipe of the elements that were likely in the planet’s early oceans. When they placed the ingredients together, raised the temperature and removed oxygen, spontaneous reactions formed compounds that are essential to the function of modern metabolism, such as glucose and precursors to nucleic and amino acid.
“This has offered a tantalizing glimpse into the prebiotic world,” says Turchyn, a fellow in the Earth System Evolution (ESE) program.
More importantly, the mixture of likely Archean ocean metals made the compounds formed by the reactions stable, meaning they didn’t turn into other compounds or degrade.
“It seems that the chemistry and lack of oxygen in the ancient ocean both facilitated and possibly accelerated cellular metabolic reactions,” Turchyn says.
All of this took place without the help of enzymes, which are the biological molecules that drive the metabolism of the living cells we see today. Researchers previously thought that enzymes must have existed on the early Earth in order to generate the conversion of carbon-sugars that eventually led to the formation of animo acids, nucleic acids and other compounds that support life. However, this research suggests enzymes might not have evolved until later.
“If these results are right, then it suggests strongly that iron concentrations in the early oceans may have been higher than we originally thought,” Turchyn says. It also suggests that the temperature of the early ocean might have been, in some local environments, as high as 70 degrees Celsius.
As an earth scientist, Turchyn brought to the collaboration an understanding of which elements were probably present in the early ocean. Her colleagues, both biochemists, conducted the experiment in her lab.
“My knowledge and appreciation of the chemistry of the early oceans came directly out of my involvement with the ESE program in CIFAR since there are lots of people who think about the big questions on early Earth,” Turchyn says.
The research was published in the journal Molecular Systems Biology