Melanin

Here is an interesting story:

Researchers at the Albert Einstein College of Medicine (AEC) have found evidence that certain fungi possess another talent beyond their ability to decompose matter: the capacity to use radioactivity as an energy source for making food and spurring their growth.

the researchers measured the electron spin resonance signal after melanin was exposed to ionizing radiation and found that radiation interacts with melanin to alter its electron structure. This, they believe, is an essential step for capturing radiation and converting it into a different form of energy to make food. Until now, melanin’s biological role in fungi – if any – had been a mystery. Interestingly, the melanin in fungi is no different chemically from the melanin in our skin, leading Casadevall to speculate that melanin could be providing energy to skin cells.

In the skin, melanin functions primarily to protect the genetic material from UV light. Melanin can also protect against free radicals and can function as an alternative electron acceptor. This newly discovered function simply adds to the overall utility of this molecule (class of molecules), explaining why it is so widely distributed among prokaryotes and eukaryotes. In fact, melanin is believed to have been spawned many times over through convergent evolution.


In addition to deep homology, convergent evolution is something that adds to the plausibility of front-loading, as convergent evolution teaches us that certain evolutionary outcomes are not all that difficult to derive. The reasons for this may differ for each example of convergent evolution. In this case, why has it been so easy for life to evolve melanin and melanin-like pigments over and over again? Perhaps part of the answer stems from the simple fact that melanin is produced through the chemical modification of tyrosine, one of the twenty amino acids coded by life. In other words, if cells were designed to use tyrosine-containing proteins, then all descendent cells would be poised to evolve melanin on an as needed basis.

And that takes us to an interesting question. There is a vast number (effectively infinite) of chemically possible amino acids that are never used by biological organisms. So why does life code the twenty that it codes? The front-loading potential is obvious, as a designer can count on these twenty being propagated far across deep time and wherever life goes (in fact, are the amino acids themselves part of some shadow code in life?). While melanin does not appear to be essential for life, it has played an important role in shaping life. Might it all stem from the simple choice to include a couple of particular amino acids as building blocks of the cell’s machinery?

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