Researchers at NASA have recently been able to persuade microbes to replace the phosphorus in some of their organic molecules with arsenic, which lies directly below phosphorus on the periodic table. This has been an unprecedented finding, as arsenic is not one of the "six essential ingredients of life;" that is, the six elements - carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur - that make up all of the natural organic molecules in life forms scientists know of now. This is especially interesting as arsenic and many of its compounds are poisonous to humans. The scientists essentially collected samples from a lake in California which possessed an extremely high salt content as well as high amounts of carbonates, phosphorus, arsenic, and sulfur. These samples were also full of bacteria and other organisms suited to live in the unusual conditions. Scientists then starved these microbes of phosphorus, and instead fed them arsenate, an analogue to phosphate, which is how organisms typically intake phosphorus. As a result, the organisms apparently replaced the phosphorus in some of their organic compounds with arsenic, and were still able to live and reproduce, albeit at a slower rate than a control group which was provided phosphorus. As arsenic lies directly below phosphorus in the periodic table, it acts much the same way as phosphorus in chemical structures. However, it is a larger molecule, and thus compounds containing arsenic are generally less stable than similar ones based on phosphorus. So far, researchers have not been able to fully explain the arsenic replacement in the microbes, as molecules built with arsenic should not be stable enough to build the arsenic equivalent of ATP, a major component in the production of energy in life forms, and other phosphorus containing compounds. While there is some speculation as to whether or not the new arsenic molecules are actually functioning parts of the organic processes of these microbes, as of now the findings are remarkable and have huge implications in the replacement of one of the essential building blocks of life.
See http://www.wired.com/wiredscience/2010/12/nasa-finds-arsenic-life-form/
Posted by Jack Ogilvie
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Very interesting! However, I think that arsenic can only replace phosphorus to a certain extent no matter how similar the 2 elements are. Just like silicon can't substitute carbon although it's directly below carbon in the periodic table. The thing is that silicon doesn't tend to form rings, long chains, etc. like carbon
ReplyDeleteChinh has a good point. It seems a little hard to believe that phosphorous, such an essential element in organic molecules such as DNA, could possibly be replaced. I suppose that makes this discovery all the more interesting. I can only imagine that sci-fi writers will have a good time creating poisonous arsenic-based aliens!
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