REHOVAT, Israel, Jan. 10 (UPI) -- Experimental new findings from an international team of scientists may help solve a great mystery concerning the origins of life -- why the primordial soup separated into molecules of one mirror image and not the other.
Researchers say all the key molecules in biology on Earth -- from sugar to DNA -- may exist in two forms. Each form contains the same ingredients but is a mirror image of its twin, similar to a pair of gloves. This handedness is found in equal proportions among biochemicals under laboratory conditions -- it is just as easy for DNA to spiral in a left-handed way as it is to twist right-handed.
Mysteriously, all organisms on Earth have an almost exclusively one-handed chemistry -- life uses only left-handed amino acids and right-handed sugars in DNA. This is of great medical significance, because different-handed forms can have startlingly different effects -- the right-handed form of the drug thalidomide quells nausea while its left-handed twin causes birth defects.
"On a molecular level, nature is not symmetrical," explained researcher Les Leiserowitz, a solid-state organic chemist at the Weizmann Institute of Science in Rehovat. "How did this come about? That's the driving force of our research."
The team of investigators have discovered new evidence lending support to theories that the very three-dimensional shapes of the building blocks of life helped separate the mirror images.
Scientists in Israel, collaborating with researchers in Denmark and France, analyzed how amino acids -- the basic components of proteins -- formed two-dimensional crystals on the surface of water, a theoretically key environment for the early development of life.
"It's really difficult to obtain long molecular chains of the same handedness if you start with mixtures of the two," explained researcher Meir Lahav of the Weizmann Institute of Science. "The longer the chain, the less likely it is one-handed."
Nevertheless, the scientists found amino acids can separate spontaneously, forming crystals of single-handedness. The three-dimensional architecture of each molecule selects identical shapes and self-assembles. As the crystals grow larger, the molecules pack tighter together and these small preferences for shape become very amplified.
The experiment still does not explain why left-handed amino acids were preferred, however.
"That's not the point of this report," commented organic chemist Peter Wipf of the University of Pittsburgh. "The kind of research that needs to be done to figure that out is to build a time machine and go back. After four billion years, there's not much 'smoking gun' type of evidence left. The smoke's had time to sort of dissipate."
Scientists have brought up a number of explanations to explain this trigger, from extraterrestrial seeding from asteroids to polarized light from the sun.
"If the theory is that the sun is the reason for the one-handedness, then you'd expect to see something similar from other planets in our solar system, like Mars or Venus," Wipf said in an interview with United Press International. "It's a kind of wild idea, but doable, very doable at this point."
In future, Lahav said his team will study how one-handed organic crystals form on mineral surfaces, another scenario scientists suggest was important in the development of life.
Scientists say more research of this kind on other planets may yield more clues to this puzzle.
"The extraterrestrial investigations of that type will be quite exciting -- by going to places like Mars or Venus, you might be able to find further evidence," Wipf said.
The researchers reported their findings in the journal Science.
(Reported by Charles Choi in New York.)
