Self-reproduction models

It is important to point out the main message of these experiments. This is that, by a very simple set-up, a spontaneous self-reproduction of spherical compartments can be obtained. Since such spherical compartments can be considered as models and/or precursors of biological cells, the hypothesis was put forward, (Bachmann et al, 1992), that this autocatalytic self-reproduction process might have been of relevance for the origin of life. 

We have also learned that self-replication is not a prerogative only of nucleic acids, but it can be shared by different kinds of chemical families see the formose reaction, the self-replicating peptides, and the self-reproducing micelles and vesicles. The list should include the cellular automata and the corresponding devices of artificial life. Self-reproduction of vesicles and liposomes is important because it represents a model for cell reproduction. 

All the models mentioned thus far are based on autopoietic self-reproduction experiments. The experimental implementation of a homeostatic mode of the autopoietic minimal system, which is also illustrated in Figure 8.3, proved to be much more difficult, and was realized only in 2001 (Zepik et al., 2001). It is based on the oleic acid surfactant system and is schematized in Figure 8.5 (respecting the theoretical scheme of Figure 8.3) there are two competitive reactions, the reaction Up forms oleate surfactant from the hydrolysis of the anhydride and the other reaction destroys oleate via oxidation of the double bond. 

Figure 8.5 The experimental implementation of the autopoietic model of Figure 8.3 with two competitive reactions. Here one reaction forms new oleate surfactant from the hydrolysis of the anhydride and another reaction destroys oleate via oxidation of the double bond. Depending on whether the two velocities are equal or not, different pathways for the systems are obtained homeostasis (which corresponds to an autopoietic self-maintenance system), growth and self-reproduction, or decay and death. (Modified fromLuisi, 1993 1996.)...

Vesicles are commonly considered models for biological cells. This is due to the bilayer spherical structure which is also present in most biological cells, and to the fact that vesicles can incorporate biopolymers and host biological reactions. Self-reproduction, an autocatalytic reaction already illustrated in the chapters on self-reproduction and autopoiesis, also belongs to the field of reactivity of vesicles. Some additional aspects of this process will be considered here, together with some particular properties of the growth of vesicles - the so-called matrix effect. 

In the meantime, the intense study of the simpler vesicle systems has unravelled novel, unsuspected physicochemical aspects - for example growth, fusion and fission, the matrix effect, self-reproduction, the effect of osmotic pressure, competition, encapsulation of enzymes, and complex biochemical reactions, as will be seen in the next chapter. Of course the fact that vesicles are viewed under the perspective of biological cell models renders these findings of great interest. In particular, one tends immediately to ask the question, whether and to what extent they might be relevant for the origin of life and the development of the early cells. In fact, the basic studies outlined in this chapter can be seen as the prelude to the use of vesicles as cell models, an aspect that we will considered in more detail in the next chapter. 

Self-reproduction of micelles and vesicles models for the mechanisms of life from the perspective of compartmented chemistry. Adv. Chem. Phys., 92,425-38. 

Ono, N. and Ikegami, T. (2000). Self-maintenance and self-reproduction in an abstract cell model. J. Theor. Biol, 206, 243-53. 

Pier Luigi Luisi became Professor Emeritus (Macromolecular Chemistry) at ETH-Ziirich in 1982, where he also acted as Dean of the Chemistry Department he is currently aprofessor of Biochemistry at the University of Rome 3. He has authored c. 300 papers in the fields of enzymology, molecular biology, peptide chemistry, self-organization and self-reproduction of chemical systems, and models for cells. 

In this Chapter we have been dealing with the simplest model of a self-reproductive molecular system consistent with known [59-61] kinetic prop-... 

Type I system. Self-reproduction of vesicles. The starting point is the concept of vesicle self-reproduction. This important vesicle pattern was observed for the first time in 1994 and thoroughly studied till recently, being one of the most important reactive behaviour of fatty acid vesicles. Figure 17.8a shows the experimental model for autopoietic... 

The original mathematical model is based on three assumed properties metabolism , self-reproduction and mutability . The simplest deterministic equation derived is ... 

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... 

Iaing77] Laing, R. Automaton models of reproduction by self-inspection, Journal of Theoretical Biology 66 (1977) 437-456. 

Section we show that presence of two such intermediate stages is more than enough for the self-organization manifestation. Lotka [22] was the first to demonstrate theoretically that the concentration oscillations could be in principle described in terms of a simplest kinetic scheme based on the law of mass action [4], Its scheme given by (2.1.21) is similar to that of the Lotka-Volterra model, equation (2.1.27). The only difference is the mechanism of creation of particles A unlike the reproduction by division, E + A - 2A, due to the autocatalysis, a simpler reproduction law E —> A with a constant birth rate of A s holds here. Note that analogous mechanism was studied by us above for the A + B — B and A + B — 0 reactions (Chapter 7). 

Qualitative studies of this dynamic model with three variables, i.e. surface concentrations of CO and the two forms of oxygen (surface and subsurface), showed [170] the possibility of interpreting self-oscillations in this catalytic system. Recently a comprehensive analysis of this model [170] has been carried out [177], Sales et al. [178, 179] determined experimentally the parameters for the oxidation and reduction of the Pt subsurface layer. The application of these parameters and those for the CO oxidation over Pt that are close to the values measured in high-vacuum experiments, made it possible to perform the quantitative reproduction, by using the model [180], of almost the whole of the experimentally observed characteristics for the self-oscillations in the reaction rate of CO oxidation over Pt. 

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