To test his theory, Krishnamurthy and his colleagues simulated early Earth conditions in the lab, using both a water base and a muddy paste set to varying pH levels. They combined DAP with different concentrations of magnesium, zinc, and a compound called imidazole that acted as a catalyst to speed the reactions, which still took weeks or sometimes months to complete.
For DAP to pass the test, it had to successfully trigger phosphorylation events that resulted in simple nucleotides, peptides, and cell wall structures under similar conditions. Past candidates for origin-of-life enzymes could only phosphorylate certain structures under wildly different chemical and environmental conditions. DAP, Krishnamurthy found, could do it all, phosphorylating the four nucleoside building blocks of RNA, then short RNA-like strands, then fatty acids, lipids, and peptide chains.
Does that mean that DAP is the pixie dust that transformed random matter into life? Not quite, said Krishnamurthy.
“The best we can do is try to demonstrate that simple chemicals under the right conditions could give rise to further chemistry which may lead to life-like behavior. We can’t make a claim that this is the way that life formed on the early Earth.”
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For one thing, Krishnamurthy has no proof that DAP even existed four billion years ago. He synthesized the molecule in his lab as a way to solve one of the fundamental challenges to phosphorylating in wet, early Earth conditions. For most phosphorylation reactions to work, they need to remove a molecule of water in the process.
“How do you remove water from a molecule when you are surrounded by a pool of water?” asked Krishnamurthy. “That’s thermodynamically an uphill task.”
DAP gets around that problem by removing a molecule of ammonia instead of water.
Krishnamurthy is working with geochemists to identify potential sources of DAP in the distant geological past. Phosphate-rich lava flows may have reacted with ammonia in the air to create DAP, or it could have been leached out of phosphate-containing minerals. Or maybe it even arrived on the back of a meteorite forged by a far-off star.
One thing is clear, without DAP or something like it, Earth might still be a lifeless mud puddle.
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