Self-maintenance

Figure 2.1 The Green Man s sketch of the living he schematizes a system composed by only one tissue S S decays into a P, but due to the internal activity of the system, the nutrient A is converted into the tissue S again. This pictorii representation corresponds to a definition of life that reads a physical system can be said to be living if it is able to transform external matter/energy into an internal process of self-maintenance and self-generation.

Figure 8.1 Schematization of the work of a cell as an open system. One important feature is the boundary, which is created by the internal network of reactions (a boundary of its own making). The network of reactions brings about a large series of transformations however under homeostatic conditions all material that disappears is generated again by the internal machinery. Thus, the cell (and by inference, life) can be seen as a factory concerned with self-maintenance.

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.)...

In addition to this known aspect of metabolism, there is another one, albeit less frequent, that refers to the interaction of novel compounds. This is important, as it gives die possibility of permanent changes, and is associated with adaptation and evolution. In odier words, one should consider two aspects of metabolism/cognition the normal homeostatic metabolism, which corresponds to die normal life and self-maintenance of the cell from within and a metabolism of novel elements diat may operate changes in die structure. 

We go back now to basic autopoiesis, in order to consider what came as an interesting, and unexpected, development of this theory. By unexpected, I mean that even the authors of the Santiago school had not foreseen it. This is social autopoiesis. The main feature of autopoiesis is self-maintenance due to a process of self-generation from within. Although this concept came from the analysis of a living cell, it can be metaphorically applied to social systems. 

Do you accept the idea that self-maintenance is the most basic property of cellular life, self-reproduction being a particular kinetic outcome of self-maintenance ... 

This brings us to the notion of the minimal cell, defined as that having the minimal and sufficient number of components to be called alive. What does alive mean Well, here we should go back to Chapter 2 and the various definitions of life however, a fairly general definition can be used here, which ought to keep everybody satisfied living at the cellular level means the concomitance of three properties self-maintenance (metabolism), self-reproduction, and evolvability (see Figure 11.2). 

If all these three properties are fulfilled, we have fully fledged cellular life. Of course in semi-synthetic systems the implementation can be less than perfect, and then several kinds of approximation to cellular life can be envisaged. For example, we can have protocells capable of self-maintenance but deprived of selfreproduction or vice versa. Or we can have protocells in which self-reproduction is active for only a few generations or systems that do not have the capability to evolve. Even in a given type of minimal cell - for example one with all three attributes - there might be quite different ways of implementation. 

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

Cells would have persisted only because of extreme efficiency in self-maintenance. In cell compartments the catalyst concentration would be a hundred to a thousand times higher than on the outside where everything is large compared to the picoliter size cell. A few protons, two to three in alysosome (a digestive vacuole), would produce pH values of 1 (the equivalent of 0.1 molar hydrochloric acid), and two enzymes in that space would bring its concentration into the millimolar range. In a cell the affinity of the enzyme for its substrate determines the speed of the reaction as opposed to thermodynamic limitations of the chemical transformation per se. 

In the open-access LC/MS procedure described by Pullen et al. " the samples are directly introduced from solution for ease of automation and sample preparation. Chemists prepare samples in solvent to a suggested concentration range, then log the samples into the system. The sample log-in is done at any time during the continuous automated queue. Autosampler vials are used to hold the samples, and autosamplers are used to directly deliver samples in solution to the mass spectrometer. The system uses a standard method to analyze the samples in queue, average spectra according to a preset scheme, and print out a spectrum for the chemist. Fail-safe procedures for untrained users and instrument self-maintenance at start-up and shutdown were also developed. 

Schwartz M Cohen IR (2000) Autoimmunity can benefit self-maintenance. Immunol Today, 21(6) 265-268. 

The probability p2 and p3 is proportional to the number of viable progeny of a RER+ stem cell, which depends on two parameters the number X of viable self-maintenance divisions of the stem cell (which in turn essentially depends on the threshold of mutations induced apoptosis), and the number N of mitoses that ephemeral colonocytes undergo in the crypt on their way to maturation (Fig. 4B). Since neither X (defined by the tolerable mutation load) nor N should vary at a given point in the colon, p2 and p3 should also remain constant throughout life, and likewise the product pt (p2 and p3). The accumulation of these rate-limiting steps of RER+ carcinogenesis can thus be assimilated to an accident that can happen any time with a constant risk. 

Probability of self-maintenance Necrotic/apoptotic cell death... 

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. 

When normal adaptability is dismpted, or when environmental changes overcome the body s capacity for self-maintenance, disease may ensue."... 

Luisi has a continuing interest in molecular evolution, autopoiesis, and the origin of life, and the matrix effect contributes to that debate. An autopoietic unit is a structure capable of self-maintenance, and this includes the option of self-replication. The work has been developed in a series of recent papers. 

Owner-driven approach house owners are responsible for rebuilding their own houses through self-maintenance with limited external financial, technical, and material assistance. 

Nakazawa, T. 1978. TOL plasmid in Pseudomonas aeruginosa PAO thermosensitivity of self-maintenance and inhibition of host cell growth. J. Bacteriol. 133 527-535. 

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