Tuesday, June 17, 2008

Murchison nucleobases

A great article today in SciAm on the Murchison molecule work by Zita Martins group. Some interesting comments, this from Robert Shapiro:"They're a subunit of a subunit of DNA," he says. "My opinion is that their amounts were utterly unimportant and insignificant" Strong words indeed. A bit of googling on Prof Shapiro indicates he has his own barrows to push. Heres an interesting article where he discusses various ideas including non carbon based life. He seems to have a track record of being dsimissive of more conventional origin research.
(I also think he misses the significance of information flow as a property of life in the linked article but then, I would).
The SciAm article finishes thus: Conel Alexander, a geochemist at the Carnegie Institution of Washington who specializes in meteorites, says that without more data, claims about the amounts and sources of molecules on early Earth should be taken with a grain of salt. "It really comes down to quantitative arguments about how much was made on Earth [and] how much was brought in from space," he says. "Any honest person would keep an open mind about the whole issue."
Well who could disagree with such a reasonable, if cautious, statement. Still the discovery of types of molecules associated with living organisms in samples representative of the early solar sytem is significant in my view. Carbonaceous chondrites like the Murchison meteorite give us an idea of the stuff that is around in early solar system formation, and while its true that there may have been only miniscule quantities present on the early earth, there may have been truckloads, nobody knows for sure yet. So any discovery of new and biologically useful (to carbon based life) molecules in such samples are important. In the Shapiro article linked above he is quoted as saying "But suppose you took Scrabble sets, or any word game sets, blocks with letters, containing every language on Earth, and you heap them together and you then took a scoop and you scooped into that heap, and you flung it out on the lawn there, and the letters fell into a line which contained the words “To be or not to be, that is the question,” that is roughly the odds of an RNA molecule, given no feedback — and there would be no feedback, because it wouldn't be functional until it attained a certain length and could copy itself — appearing on the Earth."
I don't like this, I think its a poor comparison - but you could say it would depend on number of trials, wind direction, block shape, etc. At least we might be getting an idea of which letters were available.

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