Replicated system

Biological catalysts — enzymes — are usually proteins. The development of new protein syntheses is nowadays dominated by genetic protein engineering (see section 4.1.2.6). Bio-organic approaches towards novel catalytically active structures and replicating systems try to manage without biopolymers. 

There was a sense however that the sequence that later came to be called RNA World was the most reasonable one RNA World denotes an early period in the development of self replicating systems... 

In spite of its simplicity and the visual similarity of this equation to Eq. (7), we would like to note that Eq. (11) leads to a nontrivial thermodynamics of a partially quenched system in terms of correlation functions, see, e.g.. Ref. 25 for detailed discussion. Evidently, the principal route for and to the virial theorem is to exploit the thermodynamics of the replicated system. However, special care must be taken then, because the V and s derivatives do not commute. Moreover, the presence of two different temperatures, Pq and P, requires attention in taking temperature derivatives, setting those temperatures equal, if appropriate, only at the end of the calculations. 

A major limitation in the development of anti-HCV compounds was the lack of a virus replication system. This was finally overcome with the development of a novel replicon system that directed persistent replication in a cell culture format (Lohmann et al. 1999). Using such a system, it was possible to demonstrate antiviral activity of an NS3/4A inhibitor in a cell culture assay, and demonstrate potency on par with treatment with interferon-a (Pause et al. 2003). 

Many bacterial viruses have genomes containing double-stranded DNA. Such viruses were the first bacterial viruses discovered, and have been the most extensively studied. With such a range of double-stranded DNA viruses, a wide variety of replication systems are present. In the present section, we discuss the best studied and most representative of the group, T4 and T7. The simpler, T7, will be discussed first. 

Winter, A. E. (1996), Autocatalysis and the generation of self-replicating systems , Acta Chem. Scand., 50, 469-485... 

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)...

The initial rate at which the matrix C is formed in these matrix-dependent experiments is related to the initial concentration c by a square-root dependence. This square root law of autocatalysis is found in most self-replicating systems ... 

The mechanism of the Li-Nicolaou experiment shows the manifold possibilities for oligonucleotide synthesis. However, this replication system is limited to special... 

Why can layer silicates serve as models for replication processes The answer is simple they have properties which are observed in replicating systems. Montmorillonite crystals contain similar parallel layers, the distance between which... 

The RNA world requires a system capable of self-replication as a precondition for the beginnings of life. In contrast, the surface metabolism theory proposed by Wachtershauser postulates that the initial step is metabolism, from which complex replication systems can evolve later. This metabolism would have occurred at the... 

M. Eigen describes this process roughly as follows let us consider a self-replicating system which is characterized by a quantity of information equal to N bits. The probability that a bit is incorrectly copied is w, and the selection reacts to errors by means of a selection factor S. In other words an error-free system has a selection advantage S over a system with an error. The survival criterion is then ... 

However, if a triplet genetic code system really did exist around 3.5 billion years ago, an RNA strand containing about 100 nucleotides would only have been able to code for a maximum of 33 amino acids. With 33 amino acids, the polypeptide formed would have been only two thirds as long as the insulin molecule, and it is doubtful whether such a chain length would have sufficed for an active replication system. 

Attempts have recently been made to link the RNA world with the lipid world. Two groups involved in RNA and ribozyme research joined up with an expert on membrane biophysics (Szostak et al., 2001). They developed a model for the formation of the first protocells which takes into account both the most recent experimental results on replication systems and the self-organisation processes of amphiphilic substances to give supramolecular structures. 

The origin and emergence of replicating systems The development of protein biosynthesis... 

A pre-organisation period (in which the first replicating systems evolved) and The maturation period (in which the first bacterium evolved from the first replication system). 

The theory that life began in an RNA World suggests that the first self-replicating system was a set of RNA molecules. The catalytic and informationtransferring properties of RNA indicate a possible scenario ... 

The similarities in products and pathways between interstellar molecules and terrestrial laboratory experiments imply a unity of physical and chemical laws in the universe. Given certain conditions and appropriate energy sources, the same chemical pathways will be followed to create certain products from the elements. That is not to say that life, even in primitive form, could be supported in interstellar space. The significant precursor molecules found in interstellar space are at extremely low concentrations, but if they were transported to planetary atmospheres, perhaps by comets, they might then react in the proper environment and evolve into self-replicating systems. 

Hydrogen-Bonding Templates in Self-Replicating Systems. 125... 

In the previous example the template is unrelated to the starting materials and to the final product. However, if the product formed by templation is the actual template, a self-replicating system emerges (see Scheme 42). 

Scheme 42 Schematic representation of a self-replicating system...

In 1990 Rebek reported an interesting self-replicating systems based on the Kemp s triacid derivative 82 (see Scheme 43) [112-114]. By a combination of hydrogen bonding and tt-tt stacking interactions, diamine 83 forms a binary complex with 82. In such a complex, the amine is ideally positioned to react with the activated ester in 82 yielding the ds-amide complex 84. 

Scheme 43 Rebek s self-replicating system based on Kemp s triacid derivative 82...

Scheme 44 Self-replicating system based on the condensation of aldehyde 86 and amine 87... 

These examples have demonstrated that it is possible to use the templating properties of a compound to accelerate its own formation. This is a potentially very attractive approach for the production of large quantities of a specific product with high selectivity. Furthermore, synthetic self-replicating systems also provide interesting models for their biological counterparts, which in turn could provide important clues to understand chemical evolution and indeed the origin of life itself. 

In spite of their attractive features, one of the problems usually encountered in self-replicating systems is the formation of very stable dimmers between the template and the complementary product formed. This obviously imposes important limitations to the use of self-replicating processes for the formation of large quantities of a specific product. 

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