PLURAL ORIGINS OF THE MOLECULAR HOMOCHIRALITY IN OUR BIOTA

We describe results of computer simulation calculations of mixed and h omochiral oligoribotides showing that it is possible to bind L(D)-mono mers at the terminal positions of chains built from D(L)-ribotides, bu t insertion at internal positions produces a large instability of the chains. Coupled with a proposed new mechanism for the growth of these linear polymers in prebiotic conditions, our results imply that enanti omeric cross-inhibition could have been bypassed to make all-D(L) olig oribotides dominant. We also show that racemic amino acids can form st able peptide P-strands, which rules out a similar origin for modern L- amino acids. Alternative schemes are proposed to account for the homoc hiralities of the amino acids and of other biomolecules.