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Which came first, though, the membrane or the metabolism? Gunter Wachtershauser, a patent attorney from Munich who also happens to be a theoretical chemist, believes that what we call life began as a series of chemical reactions between certain key organic molecules. Instead of being enclosed in a membrane, he says, they might have been stuck like pins in a cushion on the surface of some accommodating material. Wachtershauser's surprising candidate for this all-important material: pyrite, or fool's gold. Since the shiny crystal carries a positive electrical charge, it could have attracted negatively charged organic molecules, bringing them close enough to interact. Wachtershauser thinks these reactions could have led to the development of something similar to photosynthesis.
Still unanswered is the riddle of how these molecules came to reproduce. Chemist A.G. Cairns-Smith of the University of Glasgow thinks the answer may lie not in glittery fool's gold but in ordinary clay. The structure of certain clays repeats the same crystalline pattern over and over again. More important, when a defect occurs, it is repeated from then on, rather like a mutation in a strand of DNA. While few scientists believe such inorganic materials are actually alive, a number take very seriously the idea that clay or mineral crystals could have served as molecular molds that incorporated life's building blocks and organized them in precise arrays.
MOLECULAR ANCESTORS
Even if one accepts the fact that organic molecules can spontaneously organize themselves and, further, that these molecules might spontaneously reproduce, there remains a fundamental chicken-and-egg problem. Modern cells are made of proteins, and the blueprints for the proteins are contained in long strands of DNA and RNA. But DNA and RNA cannot be manufactured without an adequate supply of proteins, which act as catalysts in the construction process. How, then, could nucleic acids get started without proteins, or vice versa?
One solution was put forward a decade ago, when researchers discovered that certain RNA molecules can act both as blueprints and catalysts, stimulating reactions between themselves and other molecules. Up to that point, scientists had thought of RNAs as merely molecular messengers carrying genetic instructions from DNA to the cell's protein factories. Suddenly RNA was seen in a totally different light. If RNA could catalyze reactions, perhaps at some point in the past, it spurred its own replication. Then it could have been much more than DNA's intermediary: it could have been DNA's ancestor. According to this line of reasoning, the first organisms lived in an " RNA world," and DNA did not develop until life was speeding down the evolutionary turnpike.
While searching for that ancient precursor of life last April, Scripps Research Institute's Joyce stumbled on the molecule that so tantalized him. A bit of synthetic RNA sloshing around in a test tube suddenly attached itself , to a piece of protein and embarked on a course of nonstop replication. For a moment, this molecular upstart seemed close to the breakthrough Joyce had been seeking.