Chapter 24 - Selection in the Abiotic Synthesis of RNA Using Metal Ion Catalyst and Template

Abstract

The chapter describes the results of nonenzymatic syntheses of RNA and discusses the selective advantage of the contemporary natural-type RNA. In the biochemical system, synthesis of nucleic acids is conducted by an enzyme, polymerase. Nucleoside triphosphates are used as substrates, and chain-elongation reaction takes place between the terminal 3'-0H of a primer and α-phosphate of the nucleoside triphosphate. Simple metal ion catalyzes the oligomerization reaction and could play the role of a metal ion in the enzyme polymerase. Nucleotides coordinate to a metal ion with a base, phosphate, and ribose hydroxyl groups. Hard metal ions, such as alkali and alkali-earth metal ions, coordinate with a phosphate. On the other hand, soft metal ions such as silver and mercury prefer coordination with a base. Intermediate transition metal ions coordinate with both a phosphate and a base. The uranyl ion has a unique coordination property. It coordinates with a phosphate and a ribose hydroxyl group. Iron, zinc, molybdenum, manganese, and copper ions are comparatively abundant in seawater and are essential for all living organisms. Cobalt and nickel ions are essential for some organisms. The uranyl ion is nonessential and toxic for organisms, although it is more abundant than the cobalt ion in seawater. In addition, the template DNA controls the incoming substrate triphosphate. For bond formation, a metal ion such as magnesium or manganese ion works as a catalyst; RNA is also synthesized in a similar way by metal ion-dependent RNA polymerase.