Hypothesis of outer cytoplasm. Dissemination 43rd
Oparin’s hypothesis on the origin of life on Earth, updated in 1969, has gaps about the origin of RNA and DNA, as well as about the mechanisms how these molecules took control of the processes that take place inside the cellular membranes.
Neocreationist hypothesis attribute RNA and DNA structure to intelligent design but have gaps about who were the designers and what was their origin.
There is a third way due to Gunter Blobel known as the hypothesis of the external cytoplasm. According to this hypothesis, membrane formation by reactivity of some molecules, their hidrofilic-lipofilic orientation and their later invagination to lead spheres with a specific content seem possible. Each one of these spheres would consist of a double membrane and a content and it could be fixed on a bigger membrane’s surface that, when invaginated would become part of another organization, and so on until the formation of a primitive cell.
Gunter Blobel considers that cytoplasmic organelles appear, remain independent or attach to the outer surface of the coacervates but always in the outer space of the membranes.
A subsequent invagination of the membrane would cause organelles to be internalized, leading to the first cell.
This suggests that the mitochondria, ribosomes, lysosomes, golgi, endoplasmic reticulum, peroxisome, nucleus, nucleolus and centrioles were formed on the outside, were then attached to the coacervate membrane and through a process of symbiosis associated until they found a combination that originated the basic plant and animal cells.
Cytoplasm external hypothesis offers considerable advantages since it explains the formation of the different cells in different conditions and even though it does not solve the primitive RNA origin, it is the hypothesis with greater plausibility.
The hypothesis of the external cytoplasm presents relevant evidence:
(1) Most organelles are wrapped by a double membrane (this can only be explained by the invagination of a simple membrane).
(2) Symbiosis between precellular structures is possible if they are formed outside, coexist on the same surface and are then included in a higher complexity structure.
(3) The most primitive bacteria (Gram negative) have a double membrane and the most modern bacteria (Gram positive) have a single cytoplasmic membrane due
the loss of the outer membrane.
Thomas Cavalier-Smith and Gareth Griffiths are the current defenders of the external cytoplasm presented by Gunter Blobel in 1980 (G. Blobel (1980) Intracellular protein topogenesis, Proc Natl Acad Sci.; 77(3): 1496-1500).
In Divulgation we have so far published 10 blogs on the origin of life. Interested readers can find them on Divulgation nº 1 (From Oparin to Venter), nº 20 (Reflections from the hypothesis of the last universal common ancestor), nº 27 (the origin of life from antiquity to synthetic biology), nº33-1st (the origin of life and its beginning on Earth) , nº 33-2nd (primitive RNA hypothesis and panspermia), nº33-3rd (chemosynthetic protobiontics), nº 40 (advanced panspermia), nº41(Oparin abiogenic hypothesis) y nº 42 (Neocreationist hypothesis).
This series is an update on a transcendental topic for future research in disease prevention, increased productivity of animal species and improved quality of this production. We know that these issues are equally momentous for civilized thought.
Another series of blogs is presenting, in parallel, the evolution of the various types of differentiated cells and the origin of each of the organs that compound the organisms of current animals.