RNA World: First Steps Towards Functional Molecules

Abstract

This review is focused on the evolution of prebioticRNAmolecules’ from the first nucleotide’s origin towards the supramolecular complexes of RNA molecules, possessing the catalytic activities. On the assumption of the numerous experimental data known, the principal stages of the RNA World’s evolution are described in terms of the molecular complexity. Special attention is given to our study of the metal-catalyzed nonenzymatic cleavage/ligation reaction, which provides a mechanism of how the RNA molecules could elongate and diversify. Studies of the last decades provided evidences that ‘there was once an RNA world’ (Orgel, 2004). The natural selection of such complicated molecule as RNA is a low-probability outcome for the primitive system, so there are several hypotheses that some polymers of another type could forerun RNA (Joyce and Orgel, 1999; Orgel, 2003). Since the primordial catalytic RNAs from that era have been replaced by protein enzymes, the exact reconstruction of a hypothesized ‘RNA world’ is difficult, though one can verify experimentally some crucial features ofRNAworld (for reviews seeDworkin et al., 2003; Orgel, 2003). This chapter focuses on the nonenzymatic reactions that could provide the possibility of emergence of large functionally active RNA molecules required for the development of RNA world. The following three sections describe the main stages of the RNA world establishment according to their titles.