Study suggests a simple mechanism could underlie the self-replication of protocells

Recent research suggests that a simple process could underlie the growth and self-replication of protocells—putative ancestors of modern living cells. The research was published on September 3rd, 2021, in the Biophysical Journal.

Protocells are vesicles bound by a membrane bilayer and are identical to the first unicellular common ancestor (FUCA). Based on relatively simple mathematical principles, the novel model put forth that the major force urging protocell growth and reproduction is the temperature fluctuations that occur between the outside and inside of the cylindrical protocell due to inner chemical activity.

The initial motivation of our study was to identify the main forces driving cell division. This is important because cancer is characterized by uncontrolled cell division. This is also important to understand the origin of life.”

Romain Attal, Study Author, Universcience

Cell splitting to form two daughter cells involves the synchronization of many biochemical and mechanical processes involving cytoskeletal structures inside the cell. However, in the history of life, complex structures like these are a high-tech luxury and should have appeared much later than the ability to split.

Protocells should have employed a simple splitting process to make sure their reproduction, before the onset of genes, RNA, enzymes, and all the complex organelles currently present, even in the most rudimentary forms of autonomous life.

In the current research, Attal suggested a model on the basis of the idea that the initial life forms were simple vesicles consisting of a specific network of chemical reactions—a precursor of advanced cellular metabolism. The principal hypothesis is that molecules containing the membrane bilayer are produced inside the protocell through globally exothermic, or energy-releasing, chemical reactions.

The gradual increase of the inner temperature drives the hottest molecules to migrate from the inner leaflet to the outer leaflet of the bilayer. The asymmetric movement results in faster growth of the outer leaflet when compared to the inner leaflet. This differential growth amplifies the mean curvature and increases any local shrinking of the protocell until it splits in two. The cut takes place near the hottest zone, around the middle.

The scenario described can be viewed as the ancestor of mitosis. Having no biological archives as old as 4 billion years, we don't know exactly what FUCA contained, but it was probably a vesicle bounded by a lipid bilayer encapsulating some exothermic chemical reactions.”

Romain Attal, Study Author, Universcience

Even though the model suggested is purely theoretical, it could be tested experimentally. For instance, fluorescent molecules can be employed to measure temperature differences inside eukaryotic cells, where mitochondria are a major source of heat. These fluctuations can be correlated with the start of mitosis and with the shape of the mitochondrial network.

Attal states that if the model is borne out by future experimentations, it will have numerous vital implications.

An important message is that the forces driving the development of life are fundamentally simple. A second lesson is that temperature gradients matter in biochemical processes and cells can function like thermal machines.”

Romain Attal, Study Author, Universcience

Source:
Journal reference:

Attal, R & Schwartz, L (2021) Thermally driven fission of protocells. Biophysical Journal. doi.org/10.1016/j.bpj.2021.08.020.

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