A team led by an Indian-origin researcher has developed a "fascinating" new theory for how life on Earth may have begun. Their experiments demonstrate that key chemical reactions that support life today could have been carried out with ingredients likely present on the planet four billion years ago. "This was a black box for us," said Ramanarayanan Krishnamurthy, associate professor at The Scripps Research Institute (TSRI) in the US. "But if you focus on the chemistry, the questions of origins of life become less daunting," said Krishnamurthy, senior author of the study published in the journal Nature Communications. Krishnamurthy and his colleagues focused on a series of chemical reactions that make up what researchers refer to as the citric acid cycle. Every aerobic organism, from flamingoes to fungi, relies on the citric acid cycle to release stored energy in cells. The study outlines how two non-biological cycles - called the HKG cycle and the malonate cycle - could have come together to kick-start a crude version of the citric acid cycle. The two cycles use reactions that perform the same fundamental chemistry of a-ketoacids and b-ketoacids as in the citric acid cycle. These shared reactions include aldol additions, which bring new source molecules into the cycles, as well as beta and oxidative decarboxylations, which release the molecules as carbon dioxide (CO2). As they ran these reactions, the researchers found they could produce amino acids in addition to CO2, which are also the end products of the citric acid cycle. The researchers think that as biological molecules like enzymes became available, they could have led to the replacement of non-biological molecules in these fundamental reactions to make them more elaborate and efficient. "The chemistry could have stayed the same over time, it was just the nature of the molecules that changed.
The molecules evolved to be more complicated over time based on what biology needed," said Krishnamurthy.
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