by NATHAN COLLINS
Could mirror molecules in space help explain why life prefers molecules with a single-handedness?
Chiral molecules are those that come in two forms: versions that are mirror images of one another but cannot be superimposed, like right and left hands. Life seems to prefer molecules of a single chemical handedness, however. All DNA, for example, twists clockwise like the threads on a right-handed screw. Nearly all amino acids, meanwhile, are left-handed. Why one or the other? “It’s pretty well established that once an excess [of one chirality] is present, life is going to go with it,” says Brett McGuire, an astrochemist at the National Radio Astronomy Observatory in Charlottesville, Va. For instance, if DNA came in both forms, its strands would not fit together, and life probably would not have gotten far.
Although it is possible such an excess originated with meteors that brought mostly one type of molecule or another to Earth early in its history, another hypothesis suggests the origins of chirality are much older. As reported in Science, McGuire and his colleagues have discovered a chiral molecule in interstellar space. The compound, propylene oxide, exists in Sagittarius B2, a cloud of gas and dust near the center of the Milky Way.
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