Self-reproducing systems

G. Schramm, H. Grotsch and W. Pollmann (1962). Non-enzymatic synthesis of polysaccharides, nucleosides and nucleic acids and the origin of self-reproducing systems. Angew. Chem. Int. Ed. Engl., 1, 1-14. 

FIGURE 2.1.7 (a) Schematic illustration of the self-reproducing giant vesicles (i) locked precursor A is incorporated into a vesicle composed of V and catalyst C and is unlocked to produce reactive precursor A (ii) A reacts with lipophilic precursor B inside the vesicle to form vesicular molecule V (iii) new vesicles are generated as V is produced (iv) generated vesicles are extruded through the membrane to the bulk water, (b) Self-reproducing system of multilamellar vesicle [105,106],... 

Cellular automata were constructed by Von Neumann and Ulam as simple models of self-reproducing systems that mimic living systems.The Von Neumann cellular automaton is not so simple and comprises a fairly complex set of rules that specifies how the system evolves in time. Codd devised a much simpler rule that achieves self-reproduction. ° Wiener and Rosenbluth... 

Examples of self-bounded chemical structures which have the capacity to replicate are termed autopoi-etic self-reproducing systems. An autopoietic unit is regarded as a structure capable of self-maintenance by means of processes which all occur within its boundary, with the synthesis of copied structures also being possible. 

The formal study of CA really began not with the simpler one-dimensional systems discussed in the previous section but with von Neumann s work in the 1940 s with self-reproducing two-dimensional CA [vonN66]. Such systems also gained considerable publicity (as well as notoriety ) in the 1970 s with John Conway s introduction of his Life rule and its subsequent popularization by Martin Gardner in his Scientific American Mathematical Games department [gardner83] (see section 3.4-4). 

In a self-reproducing, catalytic hypercycle (second order, because of its double function of protein and RNA synthesis) the polynucleotides Ni contained not only the information necessary for their own autocatalytic self-replication but also that required for the synthesis of the proteins Ei. The hypercycle is closed only when the last enzyme in the cycle catalyses the formation of the first polynucleotide. Hypercycles can be described mathematically by a system of non-linear differential equations. In spite of all its scientific elegance and general acceptance (with certain limitations), the hypercycle does not seem to be relevant for the question of the origin of life, since there is no answer to the question how did the first hypercycle emerge in the first place (Lahav, 1999). 

At the point where amphiphiles were recruited to provide the precursors to cell membranes, stable lipid vesicles could have evolved [141] to enclose autocatalytic chiral hypercycles. Credible models for the subsequent evolution of vesicles containing self-replicating chiral molecules have appeared in the literature. [193,194] These vesicles could then emerge from the feldspar spaces [134,192] as micron-sized self-reproducing, energy-metabolizing vesicular systems protobacteria ready to face the hydrothermal world on their own terms. 

In a self-organizing system, agents pursue individual courses that are unpredictable. Reliable, reproducible structures emerge at the collective level from the interactions of those agents. Individual agents are literally out of control, but the system as a whole produces relatively stable results (see Kelly, 1994 for many interesting applications of this concept to economic life). 

A few systems of this kind were developed (Bachmann, 1990 and 1991), and this allowed the introduction of the notion of self-reproducing micelles. The... 

Simultaneous oleic anhydride hydrolysis resulting in a self-reproducing vesicle system. 

Takakura, K., Toyota, T, and Sugawara, T. (2003). A novel system of self-reproducing giant vesicles. J. Am. Chem. Soc., 125, 8134-8140. See also Takakura, K Toyota, T, Yamada, K., et al. (2002). Morphological change of giant vesicles triggered by dehydrocondensation reaction. ChemLett., 31,404-5. 

Growing membrane systems have been used to obtain artificial infrabiological systems. Walde et al. [47] have carried out the synthesis of polyadenylic acid in self-reproducing vesicles [48], in which the enzyme polynucleotide phosphorylase carried out the synthesis of poly-A, and membrane vesicle multiplication was due to the hydrolysis of externally provided oleic anhydride to oleic acid. The snag is that the enzyme component is not auto-catalytic. Enzymatic RNA replication in vesicles [49] suffers from the same problem. It is also not known whether redistribution of the entrapped enzymes into newly formed vesicles occurs or not. An affirmative answer would be evidence for vesicle reproduction by fission. 

Fig. 2 Schematic representation of a minimal self-replicating system rate equation for parabolic and exponential growth. (Reproduced from [33])...

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