Scientists Identify ‘Missing Link’ in Life’s Chemical Origins

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Before biological evolution could take off and produce the incredible variety of plants and animals we have today, there was some chemical process that gave rise to life. Scientists around the world are probing the secrets of chemical evolution, hoping to discover the reactions that produced the first self-replicating molecules. A team from The Scripps Research Institute (TSRI) in California have found a molecule that could have been integral to the development of life.

The biochemistry of a modern cell is obviously much more complex than the first phase of life on Earth, but researchers know certain things must have been the same. For example, researchers have been struggling to come up with a mechanism for a reaction called phosphorylation that could have worked under the conditions on Earth billions of years ago. The Scrips team says it has identified a compound that checks all the boxes, and it’s called diamidophosphate (DAP).

Phosphorylation is vital to biological function on Earth–your cells are doing it now on a massive scale. Many of the proteins and molecules on which our cells rely need to be modified or “switched on” in some way. Phosphorylation, which is the addition of a phosphoryl group to a molecule, is one of the primary mechanisms for that. For example, the p53 tumor suppressor protein is regulated by 18 different phosphorylation sites on within its amino acid structure.

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According to the TSRI team, diamidophosphate could have existed in water on Earth billions of years ago, and the conditions would not have prevented it from acting as a phosphorylation agent. Experiments show that DAP is capable of phosphorylating nucleosides, which are the building blocks of RNA and DNA. The addition of the simple (and abundant) organic catalyst imidazole caused these nitrogen bases to stick together in chains that look an awful lot like short strands of RNA.

Imidazole also works with DAP to catalyze the phosphorylation of glycerol and fatty acids, linking them together into self-assembling capsules called vesicles (see top). This is a primitive version of the phospholipid membranes we see in cells to this day. Phosphorylation via DAP of amino acids also caused them to link together into short peptide chains — the building blocks of proteins.

So, that’s three important classes of biological molecules that are affected by DAP. These complex interactions are just a sample of what could have happened on Earth eons ago. The TSRI team plans to continue following this line of inquiry to find potential geological sources of DAP that would have been available when life arose on Earth.

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