Despite NASA’s recent news (see my last post), arsenic is still a deadly poison to most life on Earth.  It interferes with your enzymes, changes the pH of your blood and body tissues, and messes up your nervous system, and it may have caused the death of Napoleon Bonaparte.  Yet despite all that, it’s not poisonous to all life on Earth.

Bacteria called GFAJ-1 can substitute arsenic for phosphorus, building arsenic-based proteins, lipids, and even DNA for itself.  This is a handy adaptation for any life form living in a phosphorus-poor environment.  But how can phosphorus, that friendly element, be interchangeable with Napoleon’s elemental killer?

The position of an element on the periodic table can tell you a lot about it.  For example, arsenic is located directly below phosphorus, which means they have the same number of bonding sights.  Arsenic is heavier, but it can combine with any molecule that phosphorus can.

Science fiction often talks about silicon-based versus carbon-based life, and it just so happens that silicon is directly below carbon.  I distinctly remember a biology teacher telling me (in a very angry voice) that silicon is too heavy.  No life form could survive with all those heavy silicates in its system.

It is true that GFAJ-1 grows faster with phosphorus in its system, but it’s happy to use arsenic instead if that’s the only thing it can find… even if arsenic is so much heavier.  So, Mr. Biology-teacher-who’s-probably-retired-by-now-because-that-was-a-long-time-ago, why couldn’t an alien on a carbon-poor planet use silicon instead?  I may not be a real scientist, but it sounds like silicon based life is getting a little more believable.

P.S.: GFAJ-1 was discovered and named by Dr. Felisa Wolfe-Simon.  It stands for “Give Felisa a Job.”

3 responses »

  1. stevenhamblin says:

    GFAJ-1 has set off a pretty vigorous debate in the biochemistry and biology communities; Rosie Redfield at UBC beat it with a stick, though a more accessible intro to the controversy is probably Carl Zimmer’s bit.

    As to silicon life forms, there’s a lot of reason why that might not work. Wikipedia’s entry isn’t too bad.


    • planetpailly says:

      Thanks for the comment and thanks for the links. It’s always interesting to see scientists debate.

      Dr. Wolfe-Simon has issued a statement replying to the criticism of her work. It’s a little defensive, but it’s worth reading. Click here.


  2. […] In December of last year, NASA scientists announced the discovery of bacteria which could replace their phosphorus with arsenic.  This research is still in dispute (sometimes the arguments get a little personal), but it seems researchers generally agree arsenic based life could exist somewhere, if not on Earth.  (See my previous posts on arsenic eating bacteria, “Eat Your Arsenic” and “Don’t Eat That Arsenic!”) […]


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