The Birth of the Human Cell Line

I realize the title of this article is a bit more obscure and clouded than the usual clear, easily understood topic, but I struggle with creating an adequate heading for an article filled with numerous fascinating pieces. However, I hope that by the end of this article, you will understand that any heading is underwhelming for such a topic, and you will find yourself blown away by the marvel of the cells that make up what you are – the most complex organism, ever. In this article, we will go over the pure genius of your cells, and how you came to be.

Eukaryote, Prokaryote – what’s the difference?

The reason we are starting off by distinguishing between eukaryotic cells and prokaryotic cells, is because you, the reader, are made up of eukaryotic cells – we should know ourselves before we delve into some of the amazing of the later sections of this article.

Eukaryotic cells differ from prokaryotic cells in size (between 5 – 100+ times larger), membrane (they have a nuclear membrane, prokaryotes do not), and in organelles (tend to have more and individualized organelles) [1]. There are several other ways these two cell families differ, but for the point of this article, we need only educate ourselves on a few.

Next, we should know that bacteria are prokaryotic cells, as well as many, many other cells that we have and have not identified [2].

Rise of the Human Cell

For us to continue, we need to take a huge step backwards by many millions of years. Actually, we need to step back between 2.5-2.7 billion years to the estimated beginning of the eukaryotic cell [3][4]. Remember, this is the cell line that will eventually make up your body in every way. The birth of the eukaryotic cell came in the midst of the thriving prokaryotic existence, which had come about some 1.0 - 1.5 billion years prior [4]. But, how was the eukaryote born?

Birth of the Eukaryotic Cell - Metabolism

It is thought that particular prokaryotic cells, which normally functioned alone or in loose colonies, began to integrate amongst themselves via a process called endosymbiosis [4][5]. Essentially, larger prokaryotic cells absorbed smaller prokaryotic cells via phagocytosis and began to integrate specific traits of these smaller prokaryotes [4][5]. Prokaryotes that were engulfed became the closed organelles we see in eukaryotic cells and their size began to increase to accommodate. A prime example of this is the organelle mitochondrion, which supplies energy for the cell [4][5].

Mitochondrion was once a bacteria that was phagocytosed and repurposed by the integration of its genetic material [4]. However, if mitochondria came at the birth of the eukaryotic cell, then how did the pre-eukaryotic cell survive without energy? Well, it did have energy, but that energy was supplied via anaerobic metabolism, because the Earth had little to no oxygen available at that time [4][5]. So, it is likely that our anaerobic capabilities that are thoroughly displayed during intense exercise were around before our aerobic metabolism – which we use every day to keep ourselves alive now. These aerobic bacteria came about as oxygen became more plentiful through a similar process occurring in photosynthesis mediated cells that arose at a similar time, if not earlier [4]. So, at this point, the birth of the eukaryote was established, but we are not a single eukaryote – we are made up of trillions of eukaryotic cells, how did that happen?

This is an image of mitochondria (dark ovals/circles) within a cell.
Birth of the Human Cell Lineage - Predator

It happened through the need for movement and growth material. Single celled eukaryotes began to come together as primitive multicellular beings, no more than a millimeter long, called amoebas which moved due to the adaptations of eukaryotic cells – these amoebas were closely tied to photosynthetic cells [4]. However, related to humans, were colonies of eukaryotes making up series of tiny creatures through the specialization of cells and reproduction of those cells (specialization in their function to the colony, for example: skin cells, nerve cells, etc, in humans – although humans did not exist at this time, this was the beginning of compartmentalization for structures beyond single cell eukaryotes) [4].

Now, while we understand what occurred that ultimately led for us to exist, I think it important to highlight the idea that the first eukaryote to start this process was likely highly predatory – meaning, it was capable of setting this all in motion due to its ability to phagocytose. The nucleus of the cell is thought to have come about due to the cell needing to protect its DNA from the constant movement of the cell’s cytoskeleton [5]. Not only that, the fluid, adaptable nature of the cell membrane, unlike many prokaryotes (or even eukaryotes in the plant lineage), allowed it to use this process of phagocytosis to capture other prokaryotes [5]. Finally, eukaryotes, along with other prokaryotes, were (and still are) able to gather genetic material via lateral (horizontal) gene transfer [5][6]. This process of horizontal gene transfer allows for cells to take in useful genes and integrate genes aside from simple splitting through sexual reproduction (vertical gene transfer); the cell absorbs a prokaryotic cell and integrates its genetic material into itself [5][6][7].

SUMMARY

The evolution of the eukaryotic cell is a brilliant one, and its eventual succession into a more detailed, functional unit known as humans is even more amazing. To think of intruders to our body as the harmful ones would be an injustice to the power and might of the human body which literally slaughters new comers without a second thought. To think that we focus so heavily on pathology, yet fail to appreciate the wonder of our own immune system and our growth as a cell line is a true shame for we should marvel at our own greatness.

Writer: Nicolas Verhoeven
References

[1] Prokaryotic vs Eukaryotic. (n.d.). Retrieved from http://www.life.umd.edu/classroom/bsci424/BSCI223WebSiteFiles/ProkaryoticvsEukaryotic.htm

[2] Prokaryotic and Eukaryotic Cells. (n.d.). Retrieved from http://faculty.ccbcmd.edu/courses/bio141/lecguide/unit1/proeu/proeu.html

[3] Prokaryotic and Eukaryotic Cells. (n.d.). Retrieved from http://kitto.cm.utexas.edu/courses/ch395g/fall2009/MOL190/Eukaryotes27.pdf

[4] Cooper, G. M., & Hausman, R. E. (2000). The Origin and Evolution of Cells. In The Cell: A Molecular Approach (2nd ed.). Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK9841/

[5] Alberts, B., Johnson, A., Lewis, J., Morgan, D., Raff, M. C., Roberts, K., … Hunt, T. (2015). Cells and Genomes. In Molecular Biology of the Cell (5th ed., pp. 1-42).

[6] Burmeister, A. R. (2015). Horizontal Gene Transfer. Evol Med Public Health, 2015(1), 193-194. doi:10.1093/emph/eov018

[7] Keeling, P. J. (2008). Horizontal gene transfer in eukaryotic evolution. Nature Reviews, 9, 605-618. Retrieved from http://academygenbioii.pbworks.com/w/file/fetch/65873871/nrg2386.pdf

 

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