Collectively autocatalytic sets

The Theory of Collectively Autocatalytic Sets and the Origin of Molecular Reproduction... 

The fifth theory is that of collectively autocatalytic sets, first proposed for peptides by myself (7-/0) and Freeman Dyson 11). The theory however, is broader than peptides alone, and might include a variety of polymers and metabolites (70, 72). 

A collectively autocatalytic set is a set of molecules, say A and B, both say polymers, where A catalyzes the formation of B out of B fragments, while B catalyzes the formation of A out of A fragments. It is important to stress that in such a system, no molecule catalyzes its own formation. The set as a whole achieves catalytic closure , such that each molecule in the system whose formation requires catalysis, has a last step in its synthesis catalyzed by some member of the set. 

Thus, collectively autocatalytic sets have been demonstrated experimentally for DNA and peptide systems. The next point to make is that a cell is a collectively autocatalytic set as a whole, and achieves catalytic closure as a whole. No molecule in a cell reproduces itself, the cell as a whole reproduces. 

Any set of reactions with a cyclic arrangement that additionally includes a downstream process that reproduces one of the metabolites involved in the loop collectively behaves as an autocatalytic network in which all the components of the loop are reproduced when the cycle is running [23, 24]. 

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