New Chirality Solution Proposed
It’s long been a mystery why cells use one hand of two-handed molecules, like left-handed amino acids and right-handed sugars. A new proposal solves the mystery, explaining how this phenomenon called homochirality arises naturally. Wait a minute…
“Life scientists unlock mystery of how ‘handedness’ arises,” announced a headline on PhysOrg. Dr. Thomas G. Mason, a professor of chemistry and physics at UCLA, was fascinated by the long-standing mystery of how life chooses one hand over the other when either “isoform” is equally probable. “Why many of the important functional molecules in our bodies almost always occur in just one chiral form when they could potentially exist in either is a mystery that has confounded researchers for years,” the article said.
So what is his solution? Surprisingly, it’s entropy – something we usually associate with disorder and randomness.
“It’s quite bizarre,” Mason said. “You’re starting with achiral components — triangles — which undergo Brownian motion and you end up with the spontaneous formation of super-structures that have a handedness or chirality. I would never have anticipated that in a million years.”
….”We discovered that just two physical ingredients — entropy and particle shape — are enough to cause chirality to appear spontaneously in dense systems,” Mason said. “In my 25 years of doing research, I never thought that I would see chirality occur in a system of achiral objects driven by entropic forces.“
The body of the article explains, though, that he didn’t try his experiment with actual amino acids or biological molecules. He experimented with colored equilateral triangles, imprinting them on a static surface using lithography. He perceived “superstructures” made up of parallelograms in the densely-packed arrangement.
Does this have anything to do with life? Not yet. “We’re learning some new physical rules, but the story in biology is far from complete. We have added another chapter to the story, and I’m amazed by these findings,” he said.
Good grief. Drop the self-serving hype about how amazed he was. This is stupid. Entropy is not a force. OK, so triangles form parallelograms when you artificially etch them onto an artificial surface. Big deal. This has about as much to do with living cells as a backgammon board has to do with a backgammon champion.
Amino acids are not triangles. They are 3-dimensional molecules with complex side chains. Living cells employ homochiral amino acids and sugars because they provide the optimum arrangement for structure and function of proteins and nucleic acids. They are 100% one-handed (see online book). Any deviation from 100% pure chirality destroys the protein or DNA molecule.
Even more important, the sequence of the amino acid building blocks is critical to function. Amino acids do not link together at random. They are forced together by molecular machines (ribosomes) that order them according to a genetic template, complete with proofreading.
That this silly attempt would get published in the journal Nature Communications is a sign of desperation at not having solved the mystery for over a century since Pasteur first noticed it. You know what solves it perfectly? Intelligent design. If Mason thinks he has written “another chapter” to the story, it’s a chapter in the wrong book – the storytelling book, not the science textbook.