Evolution precellular

These successes in the area of precellular structures led Daniel Segre et al. from the Weizmann Institute in Rehovot to publish the lipid world hypothesis together with Deamer. The authors are of the opinion that the (more probable) lipid world determined chemical and molecular evolution on the primeval Earth prior to the (less probable) RNA world . Further development stages (or worlds ) finally led to biogenesis (Segre et al., 2001). 

Spiegelman, S. (1971). An approach to the experimental analysis of precellular evolution. Quart. Rev. Biophys. 4,213-253. 

It follows from our foregoing discussion that such a system must be a culmination of a protracted period of prior evolution. This comprises chemical evolution (the complexification of chemical systems) and evolution by natural selection of chemical replicators of various kinds. It is likely that mineral surfaces have played an important role in precellular evolution (e.g. [9-12]). Surfaces have favourable thermodynamic, kinetic and selective effects on chemical and replicator evolution. Reviews of molecular selection dynamics on surfaces can be found elsewhere [ 13]. We mention this link because effects that surfaces can confer can be conferred even more efficiently by compartments obviously, a reproducing protocell is the strongest form of population structure, conducive to group selection [14,15] of the replicators included within. 

N. W. Gabel (1971). Excitability, polyphosphates and precellular organization. In R. Buvet and C. Ponnamperuma (Eds), Molecular Evolution, Vol. 1, Chemical Evolution and the Origin oj Life, North-Holland, Amsterdam, The Netherlands, p. 369. 

For the time being, therefore, the only reasonable conclusion is that a true replication mechanism appeared only at the end of precellular evolution, when the first cells came into being. Both chemical evolution and postchemical evolution, in other words, had to take place with metabolic systems that were able to tolerate errors, because only in this way could they be immune to the replication catastrophes. 

In addition to polymerising ribosoids, precellular systems were producing many other types of ribosoids, and, for statistical reasons, most of these were devoid of any metabolic value. A few, however, could have more interesting properties and behave, for example, like ribozymes or transfer-like RNAs. The first part of postchemical evolution was therefore a simple continuation of the metabolic processes of chemical evolution, with the difference that precellular systems were now carrying RNAs in their interior, which means that both the players and the rules of metabolism were slowly changing. 

All this tells us that the evolution of primitive ribosoids into protoribomes and ribogenomes could have produced - at equal thermodynamic conditions - a countless number of other protein worlds, and therefore countless other forms of life. In the course of precellular evolution, therefore, two distinct processes went on in parallel the development of metabolic structures, and the development of a particular genetic code that gave life the familiar forms of our world, and not those of countless other possible worlds. 

The metaphor can also be extended to earlier stages of evolution. If the origin of the first cells is likened to the origin of the first villages, we can compare the age of precellular evolution to the period of history in which villages did not exist. The interesting point is that this metaphor allows us to take a closer look at today s most popular model on precellular evolution the model of the naked gene as the first replicator (Dawkins, 1976). 

At this point, however, we cannot ignore the fact that the evolution of protein synthesis started before the origin of the first cells, in systems which could not have cell walls, cytoskeleton filaments or sodium pumps, for the very good reason that all these structures require well-developed proteins. How could precellular systems have high potassium concentrations, and low sodium levels, without any of the molecular mechanisms that cells employ to this end The most plausible answer is that those concentrations did not have to be produced in prebiotic systems because they already existed in the environment of the primitive seas. The ribotype world, in short, was also a potassium world. 

Diener TO. Circular RNAs relics of precellular evolution. Proc Natl Acad Sci USA. 1989 86 9370-4. 

Whereas most of the work discussed so far in this essay has dealt with the synthesis of well-defined biochemical species supporting the theory of chemical evolution as first proposed by A. I. Oparin, one of Oparin s major concerns has been to develop a hypothesis of precellular evolution and to experimentally demonstrate that specific biochemical reactions can occur within simulated precellular entities (coacervates). In an elegant experiment, using polynucleotide phosphorylase in coacervate droplets and the appropriate substrate in the external medium, he showed a continuous uptake of the substrate, a rapid internal synthesis of polynucleotides and a continuous release of phosphate to the external environment. His more recent concepts on evolution of probionts and the origin of cells were presented at the 4th International Conference on the Origin of Life held in Barcelona, Spain, in 1973. Experimental models involving microspheres made of polymers of amino acids have been developed by S. W. Fox and coworkers > and other investigators. 

A general mathematical treatment of the precellular self-organization of matter and the evolution of macromolecules was presented some time ago by Eigen. > A set of selectivity and evolutionary principles were derived for alternative populated states of macromolecules, leading towards states of higher complexity and information content. It would be highly desirable to analyze and correlate the three models presented thus far (molecular, co-acervate-microsphere and mathematical), select the realistic and cooperative portions of these models, and integrate them into a theory of precellular evolution which could be experimentally tested. 

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