As we approach Complete Polyploidy (CP), we can have as many as 2^78 (2,780,780) cells in the body. This is because, during the 8-cell stage of mitosis, we regularly divide the original cell by 400’000.
Why did I use the word two in the title of this article? Two reasons:
Name: differentiated cells
Starting from the 2^78 cells, 2 are selected. These are the “daughter” cells that will become the cells of an oocyte. For this reason, there is a limit to how many daughter cells can be derived from a single cell. Only one out of two oocytes can be produced from Complete Polyploidy (CP).
What is the function of oocytes?
Oocytes are produced from sperm cells (mosaic eggs) after one cell splits; the gametes that are shed are the daughter cells of the sperm. The 1/1 ratio of daughter to gamete means that only one oocyte can be produced from a single bundle of DNA from a male.
You might have heard this before; egg and sperm cells each possess DNA, but they don’t. A woman ovulates if she has enough eggs to do so. Sperm can self-fertilize but are incapable of producing a fertilized egg.
Each month, a woman will have between 40 to 50 million eggs (a million eggs per month). She must keep producing and nurturing her eggs to ensure that the population (estrogen-producing oocytes and sperms) keeps expanding (we need more eggs to keep having babies). An ovum should divide 4 times to ensure that two sets (2 oocytes per cell) can be maintained without jeopardizing the possibility of having a baby.
What is mitosis?
Mitosis is a very important process for a cell to complete. It Is a process that allows cells to step down the evolutionary ladder from (daughter) cells to (eggs).
The progression from daughter to egg is pretty simple. Each daughter cell starts as a single cell, and only after 2 divisions (400’000) from the original cell does the cell develop into an oocyte or a sperm.
There are 4 major steps in the process of cell division:
These four steps can always be assumed to continue until (polyploidy)
It is no surprise that mitosis not only ensures that we have a limited amount of cells (only one complete set of gametes, compared to 14 million+ in sperm), but it can also give us a detailed map of the entire process.
What is the basic building block of a cell?
A simple analogy to help with understanding the higher level phase of cell division is the process of folding a paperclip. You start at the top and then unfold until you reach the bottom. In the same way that cells undergo five different stages of mitosis, the beginning of a new series of cell division involves folding 10 pairs of chromosomes (20 pairs when replicated 2x), distributing them equally between the two daughter cells, then taking them apart again to repeat the process.
Now that we understand the basic four steps (combining the twinning diagram with the bilayer weave and external cell membrane analogy to better visualize the stages, and folding the paperclip analogy again back to properly visualize these four sets of cells), it becomes clearer why this process must continually be happening in a closed system. Eventually, after the unabated folding of 20 pairs of chromosomes, the cell has enough copy and distribution to generate a single cell.
What is the structure of a cell?
When you run your fingers over the 20 pairs of chromatids that are on the new and final pair of daughter cells, you realize that the coiled-up chromatids have trapped and protected the DNA as it continues to replicate, separate each daughter cell from the other just as it did in the basic set of cells. With only a few pairs of chromatids on one daughter cell, you can begin to envision how this process can quickly get out of control.
Each of the 20 sets of chromatids creates a support system for the fractured cell membrane. Fatty acids and proteins secrete on the broken membrane, allowing it to continually renew the sandwich of support proteins called a “foam core” that keeps the cell alive. As the daughter cells divide, broken foam cores (called zona pellucida) have separate functions (Figure 1)
How will a cell split continue to divide without the support system of the split foam cores? Once the process of cell division reaches a point whereby the cellular membrane thickens and surrounds the unfolded nucleus, the corresponding system of folding and mitosis tails off (Figure 2).
In this final division, the daughter cells will be like “household cats” without the help of their housemates. Without an internal support system, the father cells will no longer seal the blastema together, resulting in a large bunch of unfused blastemas in the new daughter cells. An almost inevitable lack of strong social ties resulting in cancer cells.
During The third Step Of Mitosis, What happens?
During the third step of mitosis, the cell divides once more to form a daughter cell. And during the fourth step, the new daughter cell receives a copy of its mother’s mitochondrial material.
The nuclei of the daughter cells continue receiving instructions from their mother’s genetic material and resume respiration. Thus, these new cells are in a state of in-situ transformation. This means that, during their growth and in the early stages of their metabolism, they function and grow in a similar way to the mother. But later on, their growth and metabolism diverge, thanks to the considerable differences in their acquisition of the mother’s mitochondrial material.
After the first cell division, there remains one daughter cell: daughter, and it receives a substantial amount of its mother’s genetic material, without respiration. That’s why it has the family crest.
Mom brings her sister, Mom’s Daughter (#2), to life. The daughter cells developed as a result of the first two steps of mitosis can be divided into two maternal daughter cells (#3 and #4). They receive the instruction from their mother’s genetic material and resume respiration.
Let’s go back to the daughter cells that were obtained before birth. Initially, they get just a small amount of Mom’s genetic material. After a few cell divisions, their metabolism is very specific to their mother. Therefore, the daughter cells can develop into several different types of cells. For example, in the case of a very obese person, they contain lipoprotein lipase (LPL), which helps to differentiate into adipocytes.
Then, the different cells can be further classified based on their different characteristics:
There are several interesting things one could notice about these different cell types:
This is just a simplified example. The complexities of a cancer cell are simply unendurable. One of the methods we are developing to tackle this issue is to take pre-differentiated cell populations and modify them using stem cells that have already formed in the lab.
When it comes to the entire process of cell division, it is regained through the following steps:
In summary, pre-differentiation allows us to construct different cell types with an increased degree of precision and at the same time offers safety guarantees. We also get the possibility to create tissues highly specialized to our needs. To build a whole organism, much work is required, and that is exactly what we have in mind. The future is looking very promising!
However, in practice, it does not work this way.