Self-replicating, enzyme-free chemical systems

To some extent, this message has already been accepted in the literature, as the quest for the pristine RNA world has been shifted into a pre-RNA world. In a recent paper, Orgel (2003) appears to accept the view that the action of amino acids might have possibily formed the basis of this pre-RNA world. 

Self-replicating, enzyme-free chemical systems 

Are there other types of self-replication in nature, possibly based on a quite different mechanism There are not many, but there is a famous case the formose reaction, described in 1861, and based on a reaction cycle of formaldehyde. This reaction has already been mentioned in Chapter 3, on the subject of prebiotic 

This approach utilized a particular hexanucleotide CCGCGG-p as a template a 5 terminally protected trideoxynucleotide 3 -phosphate d(Me-CCG-p), indicated as A, and a complementary 3 -protected trideoxynucleotide d(CGG-p ), indicated as B, 

The hexamer formation proceeds via the ter-molecular complex M, and the proximity between A and B in this complex facihtates their covalent linkage. Thus, once the complex D is dissociated, two T molecules are formed, and the autocatalytic self-replication process can start with the progression described above two give four, four give eight, eight give sixteen, and so on. 

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Self-replicating, enzyme-free chemical systems 1=... 

Gunter von Kiedrowski (Ruhr-University, Bochum, Germany) used two trideoxynu-cleotide substrates in experiments to study the possibility of a self-replicating, enzyme-free nucleotide system. Chemically speaking, the three symbols A, B and C represent ... 

Julius Rebek and his group were also active at about the same time with enzyme-free self-replication of chemical structures. Unhke von Kiedrowski group, he did not use nucleotides, but a rephcator consisting of an adenosine derivative and a derivative of Kemp s acid (Rotello etal., 1991 Rebek, 1994). See also Figure 7.7 for a self-replicating system not based on nucleic-acid chemistry. There are several variations of this scheme, which are not illustrated here - for reviews see Sievers etal, 1994 Orgel, 1995. 

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