Chemistry

Whence Homochirality?

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Science  05 Feb 2010:
Vol. 327, Issue 5966, pp. 625
DOI: 10.1126/science.327.5966.625-d

Just as left and right hands cannot be superimposed in space, so the carbon centers in biologically derived amino acids and sugars are locked in a single specific orientation, or chiral sense, distinct from its mirror image. An enduring question is how this circumstance came about. This month, a collection of nine papers organized by Pizzarello and Lahav explores this question from a variety of angles. Among the contributions, Green and Jain review several theories put forward over the past half-century; they emphasize that chiral selectivity is a natural consequence of the evolution of enzymes toward maximum catalytic efficiency, and they further suggest that life may have begun on both sides of the mirror, so to speak, with organisms of the presently unfavored symmetry tripped up by an early random event. Many current studies focus instead on the possibility that the preponderance of building blocks on Earth were homochiral from the outset, their configurations set by a process of asymmetric amplification from a small initial excess of one chiral sense in a precursor pool. Kawasaki et al. investigate the propensity of a chiral organic crystal to seed this sort of amplification. Taken together, the full series of papers conveys the diversity of approaches directed toward solving this deep natural mystery.

Orig. Life Evol. Bios. 40 1; 111; 65 (2010).

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