More than 3.6 billion years ago, a major transition was made on Earth whereby a dilute, swirling cauldron of simple chemical soup made a critical step towards creating the building blocks of life. The simple chemicals became amino acids, the fundamental building blocks of more complicated protein molecules. These proteins then somehow came together to form a single, primitive cell.
Although most scientists are in agreement on the journey that single cells took to becoming multicellular organisms like plants and animals, and recent research has started to reveal how simple chemicals became amino acids, a significant grey area remained. How precisely did the amino acids unite to become all-important proteins? Scientists from the Universiy of North Carolina think they are closer to the answer.
Their answer tackles the 'RNA world' theory. In today's world, RNA—DNA's chemical cousin—is crucial to the production of proteins in the cell. The 'RNA world' theory claims that RNA arose from the chemical soup, and created an RNA world before any proteins or single cells existed. These RNA strands then created the first short proteins, which manifested themselves into single cells.
However, the scientists have another suggestion: They argue that it is equally likely that little proteins were the catalysts for RNA formation, which is the opposite suggestion of the 'RNA world' theory. In fact, amino acids and other molecules swimming around in the simple soup could have co-created proteins and RNA at the same time. This new finding makes our origin story much more complicated and exciting.
The evolutionary voyage from the first single cell (lovingly called LUCA, Last Universal Common Ancestor) to humankind is a baffling and complex process. However, the basic building blocks were already in place. Compare this to the creation of LUCA: the first life form to ever exist. If life after LUCA is puzzling, then the creation of LUCA, and therefore life, is even more mystifying. Finding out what mechanisms resulted in LUCA's existence is hard to pinpoint. "We know a lot about LUCA and we are beginning to learn about the chemistry that produced building blocks like amino acids, but between the two there is a desert of knowledge," Charles Carter said. "We haven't even known how to explore it."
To test their theory, the pair examined twenty different amino acids and observed how they joined together to form useful proteins. Then they put the amino acids through their paces by testing how effectively they form useful proteins at a range of temperatures. Before life started on Earth, the atmosphere is predicted to have been extremely hot so proteins had to be able to form under these conditions.
The research found that even when the heat was cranked up, they could still link together to form proteins that were useful for the building blocks of life. "Our experiments show how the polarities of amino acids change consistently across a wide range of temperatures in ways that would not disrupt the basic relationships between genetic coding and protein folding," said Richard Wolfenden. This research brings up the question of whether an 'RNA world' ever existed or whether it was instead a 'protein world'. More research needs to be done, but the implications about our origins are thrilling.