Thursday, December 2, 2010

New Life

I just couldn't not blog about NASA's announcement today.
NASA has discovered a new life form, a bacteria called GFAJ-1 that is unlike anything currently living in planet Earth. It's capable of using arsenic to build its DNA, RNA, proteins, and cell membranes. This changes everything.
I agree that this is a big deal. We have up to now assumed that DNA had to be made up of the same elements all the time. These bacteria use arsenic (yes, that arsenic, the poison) in place of phosphorous in their DNA. The article goes on...

NASA's geobiologist Pamela Conrad thinks that the discovery is huge and "phenomenal," comparing it to the Star Trek episode in which the Enterprise crew finds Horta, a silicon-based alien life form that can't be detected with tricorders because it wasn't carbon-based. It's like saying that we may be looking for new life in the wrong places with the wrong methods. Indeed, NASA tweeted that this discovery "will change how we search for life elsewhere in the Universe."
Here's where I get lost. The Horta, as we all know, replaced carbon with silicon. Now, carbon is a big deal. Just about every molecule in living organisms relies on carbon in some way, to the extent that the term organic chemistry is used to describe chemistry of carbon compounds. Replacing phosphorous is not in my mind as big a deal, because while phosphorous is essential to life, the amount of it in a living organism is relatively small and the organism using it would still be recognizable (as opposed to the Horta, which didn't even register on the tricorder as living). Not that this isn't still a big deal, but whereas I would think the Horta would have a completely different life process, I could see this arsenic-based DNA behaving very similarly to the rest of Earth's life.

But why arsenic, of all things? In 1868 Dmittri Mendeleev began writing a chemistry textbook. One of his ideas was to arrange the known elements (60 at the time) in order of increasing weight. This had been done before, but Mendeleev noticed that when they were written in tabular form, some elements in the same columns had similar properties. This had been noticed before also, but what Mendeleev did, and which required a leap of faith, was to force similar elements into the "correct" columns based on their properties, leaving empty places in the table. Mendeleev claimed that the holes in the table were as yet undiscovered elements, and by looking at the patterns in the table he was able to predict the properties of these unknown elements.

For instance, there was a gap under aluminum in Mendeleev's table, which he called "eka-aluminum" (eka is a Sanskrit word meaning "one more than"). From the patterns in the table he predicted that eka-aluminum would be discovered to have certain properties. He predicted it's atomic weight would be around 68, its density would be around 5.9 and it would be a metal with a low melting point. In 1875, eka-aluminum was in fact discovered by French chemist Paul-Émile Lecoq de Boisbaudran who named it gallium (and there's a fascinating story in the naming of gallium as well). Gallium's atomic weight is 69.9, density 5.93, and it's melting point at 30.1° C (which means it can melt in your hand)!

At any rate, the answer to "why arsenic" is because arsenic is right below phosphorous in the periodic table (you could call it "eka-phosphorous"). In that sense it is chemically very similar to phosphorous, and can form similar bonds with similar other elements to make similar molecules that have similar properties.

As for naming gallium, at the time, the discoverer of an element got to name the element. Gallium's discoverer, who was French, claimed to have named it for France, since the Latin name for France is Gaul. However, his name was Paul-Émile Lecoq de Boisbaudran, and Lecoq means "the cock", which in Latin is Gallus. So perhaps he was naming the element for himself, rather than his country. We'll never know.


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