January 10, 2011 | David F. Coppedge

Left-Handed Amino Acids Explained Naturally?

The problem of left-handed amino acids in life’s proteins has remained an evolutionary conundrum for decades (see online book and earlier entries).  Another team has tried to tackle it, and boasted great things for their small returns.  Science Daily said,

What is the origin of such asymmetry in biological material?  There are two competing hypotheses.  One postulates that life originated from a mixture containing 50% of one enantiomer and 50% of the other (known as a racemic mixture), and that homochirality progressively emerged during the course of evolution.  The other hypothesis suggests that asymmetry leading to homochirality preceded the appearance of life and was of cosmic origin.  This is supported by the detection of L excesses in certain amino acids extracted from primitive meteorites.  According to this scenario, these amino acids were synthesized non-racemically in interstellar space and delivered to Earth by cometary grains and meteorites.

A team in France was able to reproduce the reported excess by warming up some comet-like ice.  The excess the article reported, though, is just 1.3%.  Life needs 100% of one hand or the other.  Their celebration outran their delivery: “This is the first time that a scenario that explains the origin of this asymmetry has been demonstrated using an experiment that reproduces an entirely natural synthesis,” they said.  They believe that circularly polarized light in stellar nebulae produced the slight excess.  “These findings imply that the selection of a single enantiomer for the molecules of life observed on Earth is not the result of chance but rather of a deterministic physical mechanism.”

Sorry.  1.3% doesn’t cut it.  It’s like getting 1.3% of the way to Hawaii; you’re still going to drown.  The chance hypothesis is definitely out the window (online book), so astrobiologists are desperately looking for some deterministic mechanism that can deliver 100% pure single-handed amino acids.  How many more years since Pasteur showed this to be a fundamental separator of life from non-life do we give the Darwin Party overtime to figure it out?  Game over!  Charlie lost!
    “Two competing hypotheses,” they said.  There’s the either-or fallacy in action.  The reasonable hypothesis they left out is intelligent design: single-handed proteins were purposefully chosen, because life cannot exist without it.  Their false dichotomy is like a choice between fish sticks and fish balls, when what you crave is beef.  Where’s the beef in this evolutionary myth?  It’s all racemic buns, and they deserve a swift paddling.

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Categories: Origin of Life, Physics

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