A primitive serendipity moment on ancient Earth

Tam-Tri Le, Phenikaa University (Hanoi, Vietnam)
https://orcid.org/0000-0003-3384-4827

August 11, 2022

Energy is the utmost crucial factor for organisms’ survival and biological evolution. In any living being, energy does not come easy. Complex biological systems cannot use raw physical energy sources like machines to power their functions. Humans are no exceptions, as we can think about how much people care about rather “mundane” physiological aspects such as eating and sleeping. To examine the aspect of energy usage, we need to go back to the cellular level.

Many students jokingly recite “mitochondria are the powerhouse of the cell” when they encounter anything related to biology. The role of mitochondria in eukaryotes is indeed worthy of its popularity. Mitochondria produce adenosine triphosphate (ATP), which is the power source for most biochemical processes in cells. In the mitochondria, ATP is created by aerobic respiration through the process of oxidative phosphorylation. Alternatively, ATP can be produced in the cytoplasm by anaerobic respiration or fermentation – which is much less energy-efficient compared to aerobic respiration. Plants and cyanobacteria can also make ATP through photophosphorylation. Animal cells mostly oxidize nutrients from food to generate energy for ATP production, while plant cells use photosynthesis to utilize sunlight’s radiant energy for creating carbohydrate molecules that are later used for cellular respiration.


Cyanobacteria Cylindrospermum, by CSIRO (CC BY 3.0);
https://en.wikipedia.org/wiki/File:CSIRO_ScienceImage_4203_A_bluegreen_algae_species_Cylindrospermum_sp_under_magnification.jpg

Mitochondria (responsible for cellular respiration and energy production) and chloroplasts (responsible for photosynthesis in algae and plants) are both organelles of eukaryotic cells. These crucial organelles derive from bacteria which are prokaryotic cells. Contemporary biological research suggests that the acquisition of mitochondria might have led to the emergence of eukaryotic cells and the evolution of complex life forms. This idea was proposed by Martin and Müller as the hydrogen hypothesis [1,2]. According to this hypothesis, the formation of mitochondria is the result of an endosymbiotic relationship (a symbiotic organism living inside the other) between bacteria and archaebacteria in ancient times. In eukaryotic cells, although mitochondria have their own genome, which is replicated independently of the nuclear genome, their replication process still requires proteins encoded by nuclear genes. Martin also suggests that after eukaryotes had emerged, a eukaryotic group later acquired a different bacterial endosymbiont (photosynthetic cyanobacterium) which became the chloroplasts.

The massive phylogenetic tree containing a huge diversity of eukaryotes today (and those already extinct) all started when a bacterium went inside an archaeon and established endosymbiosis. This singular event led to all kinds of complex biological traits later [3]. In a sense, this was a primitive serendipity moment – a spontaneous change that kickstarted the energy-producing systems of eukaryotic cells and allowed for the development of more advanced structures. Even in this random event between two primitive single-celled creatures, we can see the roles of directionality (optimizing energy efficiency) and conditionality (compatible cellular structures and functions). On the other end of evolution and complexity, the mechanism of innovation in the human mind and society also reflects these basic principles, although much more cognition-based [4].

References

[1] Martin, W., & Müller, M. (1998). The hydrogen hypothesis for the first eukaryote. Nature, 392(6671), 37–41. https://doi.org/10.1038/32096

[2] Martin WF, Müller M. (2007). Origin of mitochondria and hydrogenosomes. Springer.

[3] Lane N. (2015). The vital question: Energy, evolution, and the origins of complex life. W. W. Norton & Company.

[4] Vuong QH. (2022). A New Theory of Serendipity: Nature, Emergence and Mechanism. Berlin, Germany: De Gruyter. https://books.google.com/books?id=2wdsEAAAQBAJ