Self-replication components

In addition, the authors suggest that all such systems must have a semi-permeable active boundary (membrane), an energy transduction apparatus and (at least) two types of functionally interdependent macromolecular components (catalysts and records). Thus, the phenomenon of life requires not only individual self-replication and self-sustaining systems, but it also requires of such individual systems the ability to develop a characteristic, evolutionary dynamic and a historical collectivist organisation. 

The use of reactive surfaces for the specific synthesis of biomolecules, or as a model for replication processes, was first reported by Cairns-Smith and Weiss (see Sect. 7.1) and continued by G. Wachtershauser (see Sect. 7.3), as well as J. Ferris and L. Orgel. It was thus appropriate to study the stabilisation of the reaction partners in enzyme-free self-replication at surfaces with reactive properties. As early as 1995, the group of G. von Kiedrowski (then at Freiburg, Germany) bonded reacting molecules at surfaces and then added the other required reaction components to the system in a stepwise manner (the latter process is referred to as feeding ). 

Szostak et al. worked on the basis of a simple cellular system which can replicate itself autonomously and which is subject to Darwinian evolution. This simple protocell consists of an RNA replicase, which replicates in a self-replicating vesicle. If this system can take up small molecules from its environment (a type of feeding ), i.e., precursors which are required for membrane construction and RNA synthesis, the protocells will grow and divide. The result should be the formation of improved replicases. Improved chances of survival are only likely if a sequence, coded by RNA, leads to better growth or replication of membrane components, e.g., by means of a ribozyme which catalyses the synthesis of amphiphilic lipids (Figs. 10.8 and 10.9). We can expect further important advances in the near future from this combination ( RNA + lipid world ). 

Self-replication takes place when a molecule catalyses its own formation by acting as template for the constituents, which react to generate a copy of the template. Such systems display autocatalysis and may be termed informational or non-infor-mational depending on whether or not replication involves the conservation of a sequence of information [9.196]. A problem is the occurrence of product inhibition when the dimer of the template, formed after the first condensation round, is too stable to be easily dissociated by the incoming components for a new cycle. 

In self-replicating systems employing three starting constituents competition between constituents can occur [9.205]. Such processes are on the way to systems displaying information transfer, whereas the two-components ones are non-infor-mational. A shift from parabolic kinetics to exponential growth of the template concentration is required for a selection process to take place [9.197]. The evidence for self-replication on the basis of template-directed autocatalysis as in 184 requires detailed mechanistic investigation on the origin of the catalytic effects observed [9.206]. 

Scheme 12.23 Minimal self-replication model. The synthesis of replicator R is accelerated by the binding of components Cl and C2 to form a ternary complex [C1-C2-R].

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. 

MESA is the beginning of a new area of research. Now that its feasibility has been established, it can go into several directions. New areas to explore include catalysis, self-replicating systems, introduction of new forces, assembly of small electrically active components, and energy dissipating systems. A common direction in MESA will be to develop strategies that allow large arrays to assemble with high levels of precision and perfection. 

A time sequenced, homogeneous transfer of molecular information to new nucleic acid components giving rise to self replication in the form of two new daughter strands. This leads to extramolecular proliferation (transfer of information to successive generations). 

In such self-replicating DCLs, because all the components are linked by thermodynamics, the equilibrium is always reached at infinite times, which necessitates... 

The central component of this RNA World scenario is a replication system that can make copies of the genetic material to grow and produce progeny. The most basic scenario is a simple templated ligation of small oligomers in a cyclical replication scheme (13-16), but ultimately a catalytic entity responsible for this crucial function of replication would be necessary. The simplest example is a single self-replicating ribozyme that can copy itself. More elaborate scenarios for... 

Inspired by the rapidly emerging model systems of artificial life [40], we were confronted with the question of whether synthetic replicators shuffle their components to generate new hybrid replicators. To answer this, we made use of a self-replicating system developed at the same time as the adenine biphenyl replicator, but which had never been fully explored. The replicator, pictured at the top of Figure 25, was based on molecular recognition of thymine derivative (41) and xanthene derivative (40) by template (42). Coupling of the... 

DNA. The fundamental requirement of a self-replicating molecule is that it can be synthesized from two or more components for which the molecule itself is the template. It is also vital that the dimer that forms upon completion of any bond formation during the template-assisted synthesis dissociates readily so that more components can bind to the original template and its newly created twin. Lastly, there must be an available pool of components. 

Figure 5.13 Philp s simple self-replicating cycle (a) components approach template (b) components held in place by hydrogen bonds to facilitate cyclization (c) replication is complete and the hydrogen-bonded dimer prepares to dissociate...

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