Sunday, November 11, 2012
Most scientists dislike such divine-seeming interventions. But if it did not come from space, where did RNA come from? Could it have evolved from a simpler, more robust system?
have shown that if you induce AEG to polymerize (form long chains) in the presence of nucleic acids like adenine and guanine, you can get a long chain of nucleic acids bound to the peptide backbone. (The basic structure of DNA and RNA.) Since nucleic acids are robust, readily formed molecules that exist throughout the universe (they have been detected in interstellar space), this is an almost plausible model of how information-containing molecules could have formed in the primitive ocean.
Life as we know it is very conservative. Rather than discard systems that are no longer used, organisms usually adapt them for another purpose. So it seems reasonable that if organisms once used AEG for a key purpose, they should still be using it for something. Thus the headlines this week about the discovery of AEG in cyanobacteria. Cyanobacteria (blue green algae) are some of our most primitive life forms, so their use of AEG suggests that it might have used in early life on earth. We don't seem to know what bacteria use AEG for, but its existence in living things lends some credence to the PNA model of early life.
Really, though, the origin of life remains a great mystery, one that we may never solve. Even if we eventually work out a series of steps by which cellular life might have come into being, it will be very hard to show that this is what actually happened.