Self-reproducing systems and the origin of life

valich

Registered Senior Member
Self-reproducing systems are fundamental to the origin of life. The production of ATP (adenosine triphosphate), the basic energy molecule in life on Earth, is an example of such a self-reproducing autocatalytic system.

The Belousov-Zhabotinskii reaction (1951) is also self-replicating autocatylitic ocillating system; however it involves only inorganic chemicals. Therefore the search is on to find the "missing link" to a self-replicating "organic" autocatalytic system.

Early experiments have shown that organic chemicals can be created through self-replicating systems. For instance, the Formose Reaction is a self-replicating autocatylitic reaction system where glycoaldehyde reacts with formaldehyde to produce glycerolaldehyde, that then reacts again with formaldehyde producing a sugar, that then splits the molecule into two glyceroaldehyde molecules, and the cycle continues.

The basis of life involves just such a reaction in which basic sugars are transformed into other sugars in the metabolic self-replicating network. ATP may not have been the necessary energy carrying molecule used for the basis for the origin of life. We can postulate other energy carriers and metabolic pathways. Nucleotides and nucleicacids have already been experimentally created that contain phosphate groups. Therefore it can no longer be accepted that the formation of a phosphate molecule could not have occurred in the pre-RNA world, nor can it be accepted that the formation of a phosphate sugar enzyme, such as phosphofructokinase, could not have also occurred under early Earth pre-biotic conditions (phosphofructokinase is at the center of the control cycle for the glycosis/citric acid cycle producing ATP).

An allosteric control system, such as the glycosis cycle, is an example of an evolutionary structure that would've been necessary for the origin of life. Glycosis and fermentation are of the most ancient self-replicating autocatylitic systems known that created pathways within organisms. Natural selection could have then refined these pathways to evolve the evolutionary diversity in life we see today.
 
"Derivatives of the sunY self-splicing intron efficiently catalyzed the synthesis of complementary strand RNA by template-directed assembly of oligonucleotides. These ribozymes were separated into three short RNA fragments that formed active catalytic complexes. One of the multisubunit sunY derivatives catalyzed the synthesis of a strand of RNA complementary to one of its own subunits. These results suggest that prebiotically synthesized oligonucleotides might have been able to assemble into a complex capable of self-replication."

Source: "A multisubunit ribozyme that is a catalyst of and template for complementary strand RNA synthesis.," by Doudna JA, et al., Science, Mar 29;251(5001):1605-8, 1991
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1707185&dopt=Abstract

"The first claims about nanobacteria came from geologists studying tiny cell-like structures in rock slices. But in 1998 the debate took a different twist when theye claimed to have found nanobacteria, surrounded by a calcium-rich mineral called apatite, in human kidney stones...They had observed the nanoparticles self-replicating in a culture medium and claimed to have identified a unique DNA sequence. How could this be explained if the cells were not alive....After studying nanoparticles found in saliva, his team claimed that the DNA was a contaminant from a normal bacterium. "It wasn't until we couldn't get any unique nucleic acids that we suddenly realised we were being tricked," he says. The paper also said that what looked liked self-replication was just an unusual process of crystal growth." http://www.newscientist.com/article.ns?id=dn5009

Thus, the original material for life was probably not carbon-based, but a self-replicating crystal that then involved a genetic takeover from a metabolic system.
 
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