Archive for the 'Bio' Category

Tales from an RNA world: a tempting hypothesis

February 28th, 2008 | Category: Bio

What is the origin of evolution? What ingredients, methods, and environment did life need to emerge as the only known process to generate complex behavior?

For some time now, there has been a minimal hypothesis stating that RNA all by its own could support Darwinian evolution. This notion has been given the name of the “RNA world” conjecture and it is broken down into two notions. The first notion of an RNA world states that an early form of life used RNA as the only genetically encoded component. The second notion goes farther ahead by stating that not only RNA was used as a sole genetically encoded component, but that it was the first one to be used. This means that RNA alone could have spontaneously produced life given certain conditions.

The second notion is of course much less supported than the first one. However, regardless of the notion, when we talk about an RNA world, we explore the concept of life generated by the interactions of RNA with its environment. We give the molecule, with its ribose backbone and its nucleotide language, the center stage in the drama of life.

But how do we prove this? Where to start? One way is to begin inferring how ancient life worked by looking at the present state of it all. In this way, ancient genomes must be inferred and ancient metabolic models deduced from that guess. The problem is that data suggests that the RNA world would have to occur well before the appearance of LUCA (our Last Universal Common Ancestor). However, inferring an RNA only model only by looking at a model of LUCA and the workings modern life is tricky and educated-guess-like at best. Another way to the RNA holy grail is by looking at how was Earth during the early stages of life: its composition, its environment, and its astronomical accidents. An RNA world model that fits Earth’s early state can be theorized and then experimentally proved. This is far more difficult that it sounds because forming a stable strand of RNA spontaneously in an unstable atmosphere and from a restricted set of elements that we think Earth had back then is not easy. There are many complications that rise during the polymerization of ribose in such an environment and many questions of how it can polymerize in the first place.

I certainly believe that there is evidence that points to the way of an RNA world, but there is no model yet of my knowing that can withstand all the critics. One thing that is fascinating about problems like this one, that is, problems that deal with the origin of life, is that, in a sense, we are Universe staring at Universe; a being trying to desperately remember its own moment of Creation. A being trying to remember when it became different to everything else.

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