The Pre-RNA World

The wide gap between the two opposing theories, replication first and metabolism first , was analysed by Pross from the Ben Gurion University of the Negev (Israel). Pross concludes that replication came first He is convinced that a causality between the two theories can only be established if it is assumed that the replication-first thesis is correct. His analysis also shows that more of the experimental results and theoretical rationales favour the replication thesis. The author finds his assumption justified that life processes are strongly kinetically controlled and that the development of metabolic pathways can only be understood if life is considered as a manifestation of replicative chemistry (Pross, 2004). 

The considerable problems associated with the RNA world led to a search for simpler systems. Nelson et al. (2000a, b) sum up the greatest problems of the theory as follows  

The difficulties of implementing glycosidic bonds between the nucleotides under the conditions present on the primeval Earth The inability to achieve double-sided, non-enzymatic matrix polymerisation 

Efforts were concentrated mainly on the backbone of RNA, i.e., the sequence phosphate - D-ribose - phosphate - D-ribose - phosphate, which needed to be simplified without losing the most important RNA functions, such as base pairing and 

3 Antisense agents are substances (in this case oligonucleotides) which are intended to prevent illnesses, for example by blocking certain mRNA sequences. 

As Fig. 6.11 shows, the normal ribose phosphate chain of native RNA is replaced by the simpler backbone of polyamide polymers. The laboratory synthesis of these new polymers has been carried out. 

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Other studies have supported the reports of considerable stabilisation of carbohydrates by borates the thermal stability of ribose increases under acidic conditions, while glucose is favoured under basic conditions. Thus, the pre-RNA world chemistry of furanosyl borate diesters of ribose could have taken place at high temperatures and low pH. A pre-metabolism world at high temperatures and in the basic pH range would have involved glucose borates and anion borates (Scorei and Cimpoia u, 2006). 

Although the pre-RNA world is now much more the centre of scientific attention in prebiotic chemistry, there have been several attempts in recent years to understand the synthesis of oligonucleotides from the normal nucleotides by using simulation experiments (Ferris, 1998). In condensation reactions in aqueous media, there is always competition between synthesis and hydrolysis synthesis is generally only successful when supported by catalysts. 

Lazcano, A. MiUer, S.L. (1996) The origin and early evolution of life prebiotic chemistry, the pre-RNA world, and time. Cell 85, 793-798. 

Miller, Stanley L. From the Primitive Atmosphere to the Prebiotic Soup to the Pre-RNA World. Washington, D.C. National Aeronautics and Space Administration, 1996. 

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