Thursday, June 14, 2007
The Monster in the Closet...
The experiment, conducted by Sol Spiegelman of the University of Illinois, consisted of introducing the viral RNA into a medium containing the RNA's own replication enzyme, plus a supply of raw materials and some salts, and incubating the mixture. When Spiegelman did this, the system obligingly replicated the strands of naked RNA. Spiegelman then extracted some of the freshly synthesized RNA, put it in a separate nutrient solution, and let it multiply. He then decanted some of that RNA into yet another solution, and so on, in a series of steps.
The effect of allowing unrestricted replication was that the RNA that multiplied fastest won out, and got passed on to the "next generation" in the series. The decanting operation therefore replaced, in a highly accelerated way, the basic competition process of Darwinian evolution, acting directly on the RNA. In this respect it resembled an RNA world.
Spiegelman's results were spectacular. As anticipated, copying errors occurred during replication. Relieved of the responsibility of working for a living and the need to manufacture protein coats, the spoon-fed RNA strands began to slim down, shedding parts of the genome that were no longer required and merely proved to be an encumbrance. The RNA molecules that could replicate the fastest simply out-multiplied the competition. After seventy-four generations, what started out as an RNA strand with 4,500 nucleotide bases ended up as a dwarf genome with only 220 bases. This raw replicator with no frills attached could replicate very fast. It was dubbed Spiegelman's monster.
*Evolution at work in the laboratory.
In 1974, Manfred Eigen and his colleagues also experimented with a chemical broth containing Qb replication enzyme and salts, and an energized form of the four bases that make up the building blocks of RNA. They tried varying the quantity of viral RNA initially added to the mixture. As the amount of input RNA was progressively reduced, the experimenters found that, with little competition, it enjoyed untrammeled exponential growth. Even a single RNA molecule added to the broth was enough to trigger a population explosion.
But then something truly amazing was discovered. Replicating strands of RNA were still produced even when not a single molecule of viral RNA was added! To return to my architectural analogy, it was rather like throwing a pile of bricks into a giant mixer and producing, if not a house, then at least a garage. At first Eigen found the results hard to believe, and checked to see whether accidental contamination had occurred. Soon the experimenters convinced themselves that they were witnessing for the first time the spontaneous synthesis of RNA strands form their basic building blocks. Analysis revealed that under some experimental conditions the created RNA resembled Spiegelman's monster.
*Biogenesis in the lab? Well....lets be honest, its not quite biogenesis...its more pre-biogenesis. The RNA would have to form protein skins and develop into cellular organisms.....but its certainly a hint toward biogenesis.