Origin of life and its beginning on Earth: Protobiontic chemisynthesis. 3rd part of divulgation blog 33
“Alternatively to the hypothesis of RNA world, pre-RNA world and panspermy; which suggest RNA molecules in their actual form or not, of local or foreign production, as the first ways of life; the hypothesis of protobiontic chemisynthesis considers that protocells or coacervated were the first life forms.
According to this hypothesis eubionts were the first forms of life, derived from protobionts, simple living creatures with capability to incorporate substances from the environment (growth) and once reached determined size, by effect of superficial tension, they break in others (reproduction) keeping most of the facts (birth) of their parents. This hypothesis is also known like the hypothesis of the coacervated and it was formuled in 1924 by Alexander Oparin.
Historically it must be considered as a reaction to the thought, of the age, that defended spontaneous generation but did not take into account three outstanding advances, first, the researches of L. Pasteur about microorganisms, second, the evolutionist proposals of C. Darwin and, third and most important, the knowledge that the atmospheres of heavenly bodies are composed by hydrogen, metane and ammonia. These compounds suppose the existence of basic elements like carbon, hydrogen, oxygen and nytrogen with great reactive capability between them and able to form, by themselves, the basic materials for the beginning of life under certain environmental conditions.
That’s why it is supposed, also, that the atmosphere of primitive Earth may have had a similar composition and also thanks to the temperature of its surface it could have gathered water in liquid status coming from the water vapour expelled with volcanic magma. In the end it is suggested that inside temperature of the planet, ultraviolet rays and lightnings could have been energy supplies to promote reactions of the basic elements, between themselves, to produce complex organic substances.
About this hypothesis of work, in 1953, Stanley Miller raised an experiment which consisting of mixing distilled water with ammonia, metane and hydrogen gases and apply electric discharges, of almost 60.000 volts to the mixture, during 3 days. When analyzing the final solution, Miller, noticed the presence of acetic acid, ADP-Glucose, and the aminoacids glicine, alanine, glutamic acid and aspartic acid, which had been formed in similar conditions and compounds to those of primitive Earth.
Being of atmospheric forming or surface, aminoacids accumulate in surface water increasing their concentration.
The next step, to prove this hypothesis of protobiontic chemisynthesis, concerns to the studies of Sydney Fox, related to spontaneous formation of protein structure. His first works proved that under similar conditions to the ones of primitive Earth, aminoacids may form spontaneously little peptides and later works revealed that these aminoacids and little peptides are able to form closed spherical membranes called microspheres or microspherules. Fox defined these formations like protocells, protein spheres which can grow and reproduce, as an intermediate step in the origin of life.
Now we must catch the ideas that Oparin suggested which consist that proteins, when dissolved in water, form coloids which grouped by electrostatic forces, became the coacervated protobionts that may have coexisted with other enzymatic proteins and polisacharides in solution and even included in their heart.
Here we find the main problems, that the hypothesis of protobiontic chemisynthesis leaves with no solution, first, shall we call reproduction to the breaking of coacervated by the effects of surface tension?, second, how nucleic acids were formed? And, third and most important, how is genetic material introduced in protobionts and has the power the way that composition of the future membrane corresponds to a sequence directed by the genetic material recently arrived, in their heart, forcing the primitive membrane not to know about electrostatic forces which formed it, as well as the composition of the nutritive solution, external, with a selective process ruled by recently arrived material?
The hypothesis of the coacervated does not have any answer, nowadays, to the last two questions. However, it has developed an answer to reproduction issue. From the idea that most part of primitive coacervated cannot reproduce, and after their breaking they only origin polimer rests, it is been suggested that some coacervated could develop an autoreplicative mechanism. This mechanism would consist in a structure in which internal part, if the envelope was external, or in its external part if the envelope was internal, it would form an specific chemical mould for the internal and external surfaces of the coacervated. This mould, once the coacervated had disappeared, may attract compounds it could link, recreating this way the original coacervated.
If this part, about reproduction, of the chemisynthetic hypothesis of origin of life in the earliest moments could be proved and also that the chemical mould could incorporate, in its composition, molecules of nucleic acids of local or foreign production, with capability to autoreplicate and divide ( actual cell nucleous ) the same as replicate the membrane ( actual ribosomes) we would have on open way, a bigger approximation, to the origin of life as we know it actually.