Self-replication dependencies

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 ... 

Of the alkenes (Figure 5.5) only ethene has been detected and of the aromatics only benzene has been seen unambiguously surprisingly propene has not been seen despite its well-understood microwave spectrum. Of interest to the origins of life is the onset of polymerisation in HCN to produce cyanopolyynes. These molecules could provide a backbone for the formation of information-propagating molecules required for self-replication. The survival of these species in a planetary atmosphere depends on the planet oxidation would be rapid in the atmosphere of today s Earth but what of the early Earth or somewhere altogether more alkane-based such as Titan ... 

The ligation product is a copy of the template, so this represents a self-replication procedure for Pl-Cys-P2. Initial rates depend on the square root of the template concentration (a common observation, readily explained where the template is active as the monomer but present mostly as the dimer), but rates fall off, as expected, as the product accumulates. 

Two independent screens have been developed to investigate the effects of fluorinated building blocks on the interactions of the dimeric peptide assembly. The impact of fluorine side chain substitutions on the stability of coiled coil folding has been studied using temperature-dependant CD spectroscopy. The second screen is based on the ability of a-helical peptides to self-replicate. Thus, peptide... 

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. 

RNA has proven to be a remarkably malleable tool in the hands of biochemists, and a satisfactory RNA-dependent RNA polymerase ribozyme will probably be developed in the laboratory eventually. When that happens, it will be the culmination of at least a decade s worth of directed efforts, using complex combinations of rational design and in vitro evolution. It will be an important demonstration that further strengthens the case that an RNA World could have existed, but it will also show that RNA polymerase ribozymes do not appear to be a simple functionality that is likely to appear de novo from a naive population of RNA molecules. The possibility of a self-replicating RNA system less sophisticated than a general RNA-dependent RNA polymerase ribozyme cannot be eliminated. 

The process of evolution demonstrated in these studies depended on the existence of machinery for the replication of RNA fragments in the form of the Q p replicase. As noted in Chapter 1. one of the most elegant characteristics of nucleic acids is that the mechanism for their replication follows naturally from their molecular structure. This observation suggests that nucleic acids, perhaps RNA, could have become self-replicating. Indeed, the results of studies have revealed that single-stranded nucleic acids can serve as templates for the synthesis of their complementary strands and that this synthesis can occur spontaneously—that is, without biologically derived replication machinery. However, investigators have not yet found conditions in which an RNA molecule is fully capable of independent selfreplication... 

Figures 12.2 and 12.3 show the error of the evaluated self-replication rate constant as a function of the experimental error and of the variation of the input flux for emulated experiments of type (a) and (b), respectively. In the case of emulated experiments of type (a) for which the evaluation of the rate constant is based on linearized kinetic equations, the error of the evaluated rate constant depends strongly on the variation of the input perturbation. The range of the final output error (—40%,+10%) is distorted in comparison with the range of the experimental error (—20%,+20%). For small values of the input perturbation, between 20% and 40%, the output error is surprisingly small— between 10% and 0%. As the input perturbation increases, the accuracy of the method deteriorates rapidly and for large perturbations the output error is almost twice as big as the experimental error. For the emulated experiments of type (b), where the rate coefficient is evaluated from our exact response law (12.105) without linearization, the situation is different. For input perturbations between 20% and 70% the error of the evaluated rate coefficient has about the same range of variation as the experimental error (-20%,+20%) and does not depend much on the size of the perturbation. For very large input perturbations, between 70% and 80%, the output error increases abruptly. In fig. 12.4 we show the difference of errors of the evaluated self-replication...

If life is the ability for self-replication, then it can be seen why nucleic acids are considered the essential stuff of life. Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are the molecules in the cell that store and transfer genetic information during self-replication. When the cell divides, DNA first replicates, or copies, itself. Then in the new cell as in the old, DNA serves as the template for protein constmc-tion—a job that depends on the other nucleic acid, RNA. 

The same group also demonstrated that an enzymatic RNA replication can occur within self-replicating liposomes, however, with no dependency between the content and the container during the replication process. As for the previous examples, liposomes were loaded with all the necessary reagents and their self-reproduction occurred using oleic anhydride at 40 °C. This example represents an autopoietic process as the reproduction of the boundary is due to the reaction that takes place within the boundary and is catalytically induced by the boundary itself. This work is presented as the first example in which the reproduction of the membrane and the replication of the internalized RNA molecules proceed simultaneously and thus, the first bridge established between the two more accepted views on the theory of minimal life the RNA world and the cellular autopoietic view. It should be mentioned that in a former... 

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