Cellular system, self-replicating

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 ). 

Fig. 10.9 Possible reaction pathway for the formation of a cell. The important precursors are an RNA replicase and a self-replicating vesicle. The combination of these two in a protocell leads to a rapid, evolutionary optimisation of the replicase. The cellular structure is completed if an RNA-coded molecular species, for example, a lipid-synthesised ribozyme, is added to the system (Szostak et al., 2001)... 

What does your intuition say did macromolecular self-replication systems come first in the origin of life or should they be seen as the product of a mature cellular or proto-cellular metabolism ... 

Many bacterial cells contain self-replicating, extrachromosomal DNA molecules called plasmids. This form of DNA is closed circular, double-stranded, and much smaller than chromosomal DNA its molecular weight ranges from 2 X 106 to 20 X 106, which corresponds to between 3000 and 30,000 base pairs. Bacterial plasmids normally contain genetic information for the translation of proteins that confer a specialized and sometimes protective characteristic (phenotype) on the organism. Examples of these characteristics are enzyme systems necessary for the production of antibiotics, enzymes that degrade antibiotics, and enzymes for the production of toxins. Plasmids are replicated in the cell by one of two possible modes. Stringent replicated plasmids are present in only a few copies and relaxed replicated plasmids are present in many copies, sometimes up to 200. In addition, some relaxed plasmids continue to be produced even after the antibiotic chloramphenicol is used to inhibit chromosomal DNA synthesis in the host cell. Under these conditions, many copies of the plasmid DNA may be produced (up to 2000 or 3000) and may accumulate to 30 to 40°/o of the total cellular DNA. 

Cellular automata are abstract discrete dynamical systems introduced by Von Neumann in an attempt to model self-replication in biological systems [11]. A cellular automaton consists of a set of nodes, usually arranged on a regular lattice, each of which supports state variables that take on a finite number of possible values. The state variables are synchronously updated at discrete... 

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