sexta-feira, 5 de fevereiro de 2010

No (Primordial) Soup for You

Februari 2, 2010
by Michael Reilly

Origins of Life Were Not What you Think

The predominant theory of the origin of life would make a terrific setting for a space horror movie, or a particularly tense episode of Star Trek: picture early Earth, a noxious place devoid of oxygen, its young oceans choked with some kind of indiscernible ooze.

Depending on how you like your origin stories, a thunderstorm passes overhead, and lightning crackles into the broth, pouring forth ever bigger organic molecules until -- presto! -- virus-sized strands of RNA and the first replicating life is formed.

Only one problem with that, according to a new paper: where do you get the energy for early life to do anything, like, I don't know, replicate? Certainly not hanging out in a shallow sea, waiting around for some lightning to strike and cook you up some soupy dinner.

Nope, you need a hot, churning cauldron of constant chemical activity -- you need a hydrothermal vent. In new research, Nick Lane of University College London and colleagues suggest that primordial soup was a lot blander than people think, and that the dark, scalding innards of deep sea vents served as ancient apartment complexes for the first living beings.

In fact, they propose that the physical structure of the vent itself was just as important as the chemistry going on. A honeycomb of tiny vesicles inside basalt rocks would've functioned as so many interconnected test tubes and beakers in a chemistry set, bubbling away the first reactions that provided little strands of replicating molecules -- when do we get to start calling them critters? -- with tasty morsels of energy-rich adenosine triphosphate (ATP).

This type of activity would have predated the formation of the highly complex RNA molecule. As potential evidence, the team cites the fact that some enzymes and proteins crucial to modern cell function have tiny cores made of iron and sulfur. If that's true, it means the first cogs and sprockets of what would eventually become a living cell were built on minerals crystallized out of seawater.

It makes almost head-smacking amounts of sense. Why would life try to build RNA first? It's the equivalent of erecting a skyscraper before you learn how to play with blocks.

And the vesicles themselves were another crucial component, according to the team's theory, providing a gradient across which chemical business could be conducted. They were so useful, in fact, that creatures mimicked them by inventing the cell wall. And what an innovation it was. Suddenly life was portable, and the race to find nutrients in new places -- indeed, to colonize the entire planet -- was on. It hasn't stopped since.

Source: BioEssays(pdf) via ScienceBlog


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