Bench Press

One thing that biologists have learned quickly is that evolution can easily solve problems that we can only dream about understanding. A key part of the power of evolution comes from the fact that biological systems are self-replicating; cells divide and make copies of themselves, organisms give rise to offspring, and so on. Biochemists have been using so-called “directed” evolution in order to engineer really cool new proteins and molecules, such as a whole spectrum of new fluorescent proteins that Roger Tsien (2008 Nobel in Chemistry) made.

In the last decade or two, chemists have started to experiment with chemical, non-biological systems that are self-replicating, by using catalysts that make more of themselves. This autocatalysis, as it’s called, can lead to some surprising findings, such as the one published this week in Science magazine.

Some molecules can come in two mirror image forms called enantiomers that behave exactly the same way, except one is left-handed and the other is right-handed. Not all molecules have a “thumb” that makes them have the hand-like asymmetry, but by tweaking a symmetric molecule, one can add a thumb to make them have an enantiomer. The “thumb” that breaks the molecule’s symmetry can be anything from a huge cluster of atoms, in which asymmetries are easily detectable, to a tiny substitution for a different isotope, in which asymmetries are nearly undetectable.

The authors constructed a catalyst that makes more of itself from a pool of “fuel” molecules. The key thing here is that these fuel molecules are asymmetric; they each have on Carbon-12 isotope on one side, and one Carbon-13 isotope on the other side. There’s just slightly more of one enantiomer than the other. Surprisingly, the catalyst, because it makes more of itself, biases new copies of itself to one mirror form, which causes more bias in the newer generations of copies. At the end of the reaction, when all the fuel is spent, the catalyst is dramatically enriched in one mirror form over another, even though the system that started was only ever-so-slightly, almost undetectably biased in one form.

One of the big questions about the origins of life is about things like asymmetry. All organisms have bias in their molecules for one particular mirror version, but where this asymmetry came from is hard to analyze. One theory that’s growing in popularity is about autocatalytic systems: a small initial bias for one mirror form got amplified over time by self-replicating chemistry, until finally when life started, the molecules were all asymmetric in the same way. As a sort of modern confirmation of that theory, this study shows that even the smallest, most trivial of asymmetries can be amplified by self-replicating systems. Whatever the real history of life is, we do know that nature can pull off some amazing feats that still boggle our minds.