The molecular orientation of compounds brought to Earth by meteorites could have determined the world's chemistry long before life began, according to a new study published online today (Mar. 16) in the Proceedings of the National Academy of Sciences
The Scientist: Did lefty molecules seed life? - The Scientist - Magazine of the Life Sciences
http://www.the-scientist.com/blog/display/55510/#ixzz0kYoCHIhPAmino acids come in left-handed and right-handed forms, which, like a pair of human hands, are mirror images that cannot be superimposed onto each other. Yet living organisms use only the left-handed version, which presents a conundrum: There's no biochemical reason why one mirror image should be better than the other, so scientists have long debated whether life's left-handed leaning arose because of random processes or whether rocks from outer space seeded a southpaw solar system.
The current study argues for the latter possibility by showing that some extraterrestrial meteorites contain an abundance of left-handed molecules. "The implications are that all life in our solar system could be the same handedness as life on Earth," Jeffrey Bada, a geochemist at the Scripps Institution of Oceanography in La Jolla, Calif., who was not involved in the research, told The Scientist.
Daniel Glavin and Jason Dworkin, astrobiologists at NASA's Goddard Space Flight Center in Greenbelt, MD, compared the ratio of left- and right-handed 5-carbon amino acids found in six primitive, carbon-rich meteorites that have an elemental composition similar to that presumably found in the early solar system. Three of these rocks were heavily left-skewed, while the remaining three showed equal handedness, or chirality, the researchers found. Of the lefty rocks, the meteorite that fell on Murchison, Australia, in 1969 -- arguably the most widely studied carbonaceous meteorite in the world -- contained the largest imbalance ever observed: a 18.5% excess of the left-handed form of the amino acid isovaline.