SELF-REPRODUCING SYSTEM CAN BEHAVE AS MAXWELLS DEMON - THEORETICAL ILLUSTRATION UNDER PREBIOTIC CONDITIONS

The recent discovery of polymerase activity in a ribosomal RNA interve ning sequence as well as other studies of RNA-replicating systems sugg est that the first living molecules were RNAs called replicases. Accor ding to this suggestion from biochemical studies, the replicase system is chosen as the simplest case of self-reproducing systems, and the f undamental problem of ''what is life'' is theoretically investigated b y analysing the behavior of a replicase system with a supply of organi c materials under prebiotic conditions. In this analysis, it is essent ial to consider (i) self-reproduction on the basis of its own informat ion, (ii) maintenance and improvement of the information by selection and (iii) environmental event of non-biologically generating organic m aterials from inorganic matter by photochemical reactions, probably oc curring in prebiotic conditions on the Earth. The replicases can retai n and further elevate their self-reproducibility through competition a mong their descendant mutants for acquiring a limited quantity of mate rials, if the initial ability of self-reproduction and the concentrati on of replicases are above some critical values. By this selection, th e replicase molecules retain a narrowed range of nucleotide sequences, or a state of lower entropy, against the natural tendency of sequence divergence, but this entropy reduction is sufficiently compensated by the entropy production in the environmental event of energy conversio n from photons to heat. Once the stability of a self-reproducing syste m is established in the above sense, the self-reproducing system can o perate as Maxwell's demon to regulate the outside flow of matter by it s catalytic function without any contradiction to the second law of th ermodynamics. (C) 1998 Academic Press.