Friday, November 04, 2005

Clay as a scaffold for the origins of life

Nature news has a spot about some remarkable chemistry displayed by aluminum-silicate clays. Under conditions mimicking undersea hot vents, these clays are able to catalyze conversion of methanol to complex organic molecules. The work reported this week adds a new twist: at least one kind of clay, smectite, can also protect the organic molecules from degradation, and might even carry them safely away from the vent and release them elsewhere.

Life as we know it has a boundary- a cell wall, defining the living thing- and information molecules. Both of these features are so basic to what we consider life that it is a major puzzle which element could have come first. For example, it's hard to assemble DNA from its units without something to keep everything near at hand; thus a cell wall seems critical. However, a bag full of goodies doesn't have much chance in the game of life without the information to make copies of itself.

The clay line of thinking provides a way to make long molecules such as DNA without relying on a cell wall. Clays instead are very "sticky" for carbon-rich molecules, which can move along the surface of the clay and interact and react with each other in two dimensions rather than three. This feature of clays provides a potential substitute for the "corral" or scaffold that the cell membrane provides in life as we know it. Thus this line of thinking champions the idea that information molecules came first in the origins of life.

One hole in this theory-- literally!-- is that current cell walls don't just keep important things in, they also protect them. Cells with walls can control their internal pH and other aspects of their insides, because they're enclosed. A growing DNA molecule out on a clay surface is exposed to whatever the hot vent can throw at it.

So the significance of the current work is that smectite not only simplifies the organization problem, but also protects the organic molecules which result. Thus organic molecules can not only arise in the hot vent chemistry, but they also have a place to hide once they're made.

Technical note: A sidelight of the articles as written is that smectite will actually release the organics if the temperature comes down to that of the surrounding ocean. Since hot vents-- also known as chimneys or smokestacks-- expel all sorts of particles out into the ocean, you could imagine a it seeding the whole area around it with these newly forged molecules. In this scenario, you'd have a lot of things then- a gradient of temperatures and chemistry, and a mechanism for physical flux- that could be very helpful in initiating natural selection on the organic products.

A newspaper writeup is at the Guardian .
The abstract in Geology Magazine is here

A very nice general intro is at Biocrawler, which seems to be a biology version of Wikipedia-- read especially the entry on Wachtershauser. Anyone heard of Biocrawler before?

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