December 3, 2008 | David F. Coppedge

Another Attempt to Explain Life’s Handedness

Life uses only single-handed (homochiral) molecules for proteins and DNA.  How that came about when mixtures of life’s building blocks contain equal amounts of both hands is a puzzle that confounds origin-of-life research.  Science Daily reported on new studies at the Argonne National Laboratory that show that molecules in space on a magnetic substrate exposed to X-rays can lead to an excess of one hand over the other.
    The article did not say how large the excess is, or whether it persists as the molecules land on earth.  It did state several times that this has been a big puzzle:

“Understanding how the molecules necessary for life originated is one of the most basic scientific questions in biochemistry,” Argonne chemist Richard Rosenberg said.  “Chirality plays a fundamental role in biological processes and researchers have been trying to discover the mechanisms that led to this property for years.

If “pre-biological molecules” on an iron meteorite were subjected to X-radiation, the spin polarization of secondary electrons on the substrate, interacting with molecules like amino acids adsorbed onto the substrate, might lead to an excess of one hand over the other, he explained.
    Still, Science Daily admitted that “The inception of chirality from the elementary building blocks of matter is one of the great mysteries of the origin of life.”  The best that origin-of-life researchers have been able to come up with is a slight excess of one hand over the other.

Biology uses 100% pure one-handed building blocks: right-handed sugars in DNA and RNA, and left-handed amino acids in proteins.  (The hand convention is purely a human rule about 3-D orientation of side groups on these molecules in geometric space.)  The two hands have equal probability of formation.  That is why natural mixtures contain equal amounts of each hand, and why biology stands out as the amazing exception.  There is no known natural mechanism to isolate one hand from the other without intelligent design.  A slight excess, usually a few percent, is not going to help, because one wrong-handed molecule on a chain ruins the chain.  In addition, there is no guarantee that the slight excess, if any, achieved under special conditions in space will be preserved and concentrated if the molecules survive entry through earth’s atmosphere.  More likely, they will racemize (i.e., randomize again into a 50-50 mixture).
    The article should be more honest about how difficult this problem is and not make it seem like progress has been made at understanding the origin of life.  “Possible Mechanism For Creating ‘Handedness’ In Biological Molecules” is the misleading title.  Are they kidding?  This is not even close enough to win at horseshoes.  Showing a picture of a man operating an X-ray photoelectron spectrometer is a distraction.  He’s got all one-handed molecules inside him.  The machine doesn’t.  He may be touching it, but there’s a huge gap between his hand and the machine, except that both show evidence of intelligent design.
    The handedness of biological molecules is only a mystery for those who make it so by insisting on an arbitrary rule that excludes intelligent causes.  Arbitrary rules are made by fallible humans.  You’ll notice that the man is operating the machine, and not vice versa.  And which object is asking the questions?

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Categories: Origin of Life, Physics

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