Could Weak Neutral Currents Have Determined Biological Chirality?

Abstract

One of the most notable examples of broken symmetry in nature is the chirality of all terrestrial biochemistry. Chemical chirality exists because complex molecules, in particular organic molecules, are in general not superposable on their mirror images. Thus most of the amino acids can exist in either a left- (L) or right-handed (D) form. However the functional proteins in nature are virtually all composed of exclusively the L amino acids. In terms of their chemical properties the L and D molecules are effectively identical, so an all D system would function equally well. Now, non-biological syntheses of amino acids in general produce equal amounts of D and L; in particular the chemical environment from which life evolved was probably without any particular chirality. So the origin of life must have involved the breaking of chiral symmetry. How this happened is a question which many people have speculated about, starting notably with Louis PASTEUR [1].