Minimal self-replicating system

Fig. 6.5 Scheme necessary for a minimal self-replicating system with an autocatalytic reaction cycle (von Kiedrowski, 1999)... 

Fig. 6.6 Schematic representation of the first minimal self-replicating system. The hexameric product obtained from linking the two trideoxynucleotides can itself function as a matrix (von Kiedrowski et al., 1992)...

Minimal self-replicating systems. Curr. Opin. Chem. Biol, 8, 634-9. 

Kassianidis, E., Philp, D., Design and implementation of a highly selective minimal self-replicating system. Angew. Chem., Int. Ed. 2006,45, 6344-6348. 

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

Fig. 1.5. A minimal self-replicating system. In the presence of template A, the two reactands on the left are organised in a way suitable for a 1,3-dipolar cycloaddition reaction. The pyridineamide part of the template recognizes the acid substituent in the reactand, while the second reactand is recognized by the carboxylic acid incorporated in the template. Particularly interesting is the fact that template A favors its own formation, while the other stereoisomer B is formed only in low amounts.

Later, suitable a-helical peptides have been shown to self-replicate as well [42]. In the context of supramolecular chemistry most interesting are however organic minimal-replicators [43] which are not based on biomolecules. Figure 1.5 shows an example for a minimal self replicating system, which operates even in a chiro-selective way. One given enantiomer of the template catalyzes its own formation, while the other enantiomer is by and large suppressed. 

A structurally simple minimal self-replicating system, J. M. Quayle, A. M. Z. Slawin and D. Philp, Tetrahedron Lett., 2002, 43, 7229. 

Figure 1. Artificial replicators and matrices (left to right and top to bottom) Rebek s distant nucleoside [6k-m] and v. Kiedrowski s amidinium-carboxylate [7f replicators Lehn s chiral organic [7g] and ele-mentorganic [7h] helicatcs v. Kiedrowski s 6a,b,d-g] and Orgel s [6c] "minimal self-replication systems Hoffmann s alienated nucleic acids [2f, 5c, 7b, lOe] and Luisi s minima-vita approach [5f,g, 8a-d] Eschenmoser s hexosc-nucleic-acids [15], compared with Olson-type R/DNAs and hypothetical nucleation dynamics of nucleoprotein systems [2f, 3k, 5c].

Figure 7.6 Minimal representation of a cross-catalytic self-replicating system. (Adapted from Burmeister, 1998.)...

It is fully within this context when, in addition to the nucleic acid-nucleic acid analog pioneering triad of self-replication systems, a fourth innovative approach adds to the minimal systems of preferentially... 

Figure IS (a) Synergistic constitutional relationships observed at two length scales within the chemical system described in (b). (b) A model of minimal self-replicating DCL. For clarity, the growth/division cycles of micellar structures are not represented. (Reproduced from Ref. 50. Wiley-VCH, 2009.)...

This part provides an abstract description of the minimal core components, processes, information stores, and structural requirements of an artificial self-replicating system. Part 2 will cover physical considerations for implementing such a design, and Part 3 will cover speculative ideas for what the existence of self-replicative processes in nature indicates on the larger scale. 

The minimal cell, as the simplest system which has all the required properties of life (metabolism, self-reproduction and the ability to evolve), is presently studied as part of a new research discipline synthetic biology. This includes subjects such as synthesis in branches of biological systems, for example, of new RNA species, new peptides and new nucleic acid analogues, as well as the synthesis of peptide nucleic acids. One example is the work of M. R. Ghadiri and G. von Kiedrowski on self-replication of oligonucleotides and oligopeptides (Luisi, 2006b). 

Luisi, P. L. and Varela, F. J. (1990). Self-replicating micelles - a chemical version of minimal autopoietic systems. Orig. Life Evol. Biosph., 19, 633 3. 

A minimal model for self-replication is shown in Scheme 12.23. The replicator (R) must be able to recognise and bind at least two different precursor components (Cl and C2) in a ternary (three component) complex, and to accelerate their chemical reaction with each other to produce a product that is a copy of the original R. Such a simple system will always be in competition with the uncatalysed binary reaction of Cl and C2. 

It is, indeed, just this native complexity which for our today s chemistry provides provocation and stimulation, intimidation and temptation, love and hate and fate together. The present artificial systems still remain utterly outclassed by even the most primitive life forms such as RNA-viruses. The possibilities of describing natural selection behavior according to quasi-species distributions in the extreme multidimensionalities of sequence spaces [3d, e] are, for artificial systems, at best a very distant utopia. With all its early primi-tivity, but also with its promising inherent potential of minimal models of self-replication [6,7,9] and - just to follow - minima vita models [8], chemistry, nevertheless, is gaining new qualities by retracing transitions to life. 

---