Dr.  Jianfeng  Xu
MRC (Medical Research Council) Laboratory of Molecular Biology,  UK

Title: Prebiotic synthesis of enantiopure RNA and DNA building blocks

Abstract:

RNA world hypothesis suggested RNA was not only acting as enzyme to catalyse key reactions to maintain life, but also the storage of genetic information on early earth. However, extant biology, in contrast to the proposed RNA world theory, features DNA as the central information-carrying molecule. To circumvent this potentially problematic transition, an RNA/DNA world has been proposed, in which nascent biology had access to both RNA and DNA building blocks from the outset. Harnessing UV light as energy source, sulphite or sulphide as reducing power, DNA and RNA building blocks are co-produced via thioanhydronucleosides in the same localised geochemical scenario, which strongly suggests RNA and DNA are molecular siblings on early earth, as opposed to one being the parent of the other. Whilst the prebiotic syntheses of canonical ribonucleosides or deoxyribonucleosides still remain an attractive goal in the field of origin of life research, recent studies indicate some modified nucleosides found in extant biology are also prebiotically plausible. The composition of canonical and non-canonical nucleosides could have been narrowed to those existing in extant biology by selection pressures from chemical and early biological evolution. UV irradiation has been considered as one of the major chemical selection pressures available on early Earth. In the prebiotic synthesis of RNA and DNA building blocks, a common precursor known as ribose-aminooxazoline (RAO) is utilized with its unique crystallization properties. Homochiral crystals of (enantiopure) RAO can be obtained from its fully racemic solution on a magnetic mineral surface due to the chiral-induced spin selectivity (CISS) effect. Thence, all nucleosides (including ribonucleosides and deoxyribonucleosides) derived from RAO could have been enantiopure when they were synthesized from RAO on early earth. 

Key words:  prebiotic chemistry, nucleosides chemistry, photo chemistry, RNA, DNA.

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