Graded Autocatalysis Replication Domain Model

An important question is whether a rudimentary genetic memory may emerge based on statistical rules of mutually interacting catalytic reaction networks. The basic idea of such a compositional genome is that in a mixture of relatively simple chemicals, the array of relevant concentrations may be viewed as a vehicle of information storage. According to Morowitz[ ), memory can also exist without specific macromolecules, but may be initiated in a chemical network with catalytic loops and reflexive autocatalysis in which the same catalyst participates in different networks. 

The Morowitz boundary is defined as Pb = 0.5. At large values of r, Pb approximates 1 and the system reproduces. One can consider this to be due to the redundancy of the system, so that upon replication the key autocatalytic cycles are easily transmitted. 

The model systems described so far belong to the class of the so-called Replicative-Homeostatic Early Assemblies (RHEA). The concept of homeostasis and the idea of self 

In the Lattice Artificial Chemistry model and also in later extensions of the GARD model, formation of the membrane itself is explicitly included. In GARD every species Aj may, in principle, catalyze every possible reaction in which another species A is formed/decomposed, with a catalytic probability Pij. This / matrix defines the chemical structure of the (auto) catalytic networks. The role and formation of the amphiphilic assembly that becomes the enclosing membrane can be incorporated into the catalytic network by assuming that the same molecules that form the assembly are also responsible for the mutually catalytic functions. This is a model that contains similarities with the sulfide protocell systems discussed earlier. The results of numerical simulations based on extended GARD model versions demonstrated the spontaneous emergence of catalytical assemblies that tend to lie below the Morowitz boundary. 

In the above models, interest was focused on evolutionary system development to 

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