The very first life to have existed on Earth may have begun when chemicals started to cooperate.
A new study suggests that life is most likely to have formed when at least two kinds of carbon-based chemicals interacted.
Sijbren Otto at the University of Groningen in the Netherlands and his colleagues have found that mixtures of simple carbon-based chemicals can spontaneously form elaborate molecules, which can then copy themselves. Such self-replication is a hallmark of life, because it allows organisms to reproduce.
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Researchers who are trying to figure out how life began have struggled for decades to make self-replicating molecules. There have been some successes, but the resulting molecules have always been carefully designed and rather elaborate.
It seemed unlikely that these molecules formed by chance on Earth, even over the course of millions of years. 鈥淭hey don鈥檛 emerge very readily,鈥� says Otto.
Self-replication
His team combined two kinds of chemicals, both of which are essential to life as we know it. The first were amino acids, the building blocks from which proteins are made. The second were nucleobases, which are crucial components in nucleic acids like DNA and RNA. Both are thought to form naturally.
When the team mixed the chemicals together, the amino acids and nucleobases linked together into ring-shaped molecules. Sets of these rings then assembled into cylindrical stacks.
The stacks could copy themselves by somehow encouraging other rings to stack together in the same way. The mixture had to be shaken for this to work, but otherwise Otto鈥檚 team didn鈥檛 have to intervene.
The study is one of several in recent years that have offered clues about a new theory of the origin of life. Previous hypotheses often assumed that one crucial chemical arose first and formed a simple kind of life, which later made all the other chemicals and became more elaborate.
The study is one of several in recent years that have offered clues about a new theory of the origin of life. Previous hypotheses often assumed that one crucial chemical arose first and formed a simple kind of life, which later made all the other chemicals and became more elaborate.
The RNA world hypothesis proposes that life began with nothing but RNA. Other researchers have imagined life starting just with amino acids, which formed simple proteins.
鈥淣ow we鈥檙e starting to see a lot of evidence for the fact that there possibly was coevolution,鈥� says Kate Adamala of the University of Minnesota in Minneapolis. 鈥淪imple RNA and peptides or amino acids have been coevolving and helping each other out.鈥�
Journal of the American Chemical Society
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