Autumn is a season of tinged leaves. The trees that boasted about their green leaves in midsummer and made dense forests change the color of their leaves one by one. Tinged leaves present the final magnificent view with all their strength and become fallen leaves. The falling leaves may look lonely, but the trees are preparing the cold winter when they cannot get enough water and nutrients by dropping the leaves. It’s also preparation for the upcoming spring because the leaves make space available for new sprouts.
An action that is similar to the leaves falling in the autumn is also taking place inside our bodies. It is the programmed death of the cell, called apoptosis. Apoptosis is derived from a Greek word that describes the green leaves of plants withering and falling, or petals falling. Just as a tree drops its own leaves to prepare for spring when it grows new leaves come out and blooms, apoptosis is the process of programmed cell death where cells kill themselves to benefit the organism as a whole.
The death of cells, which is caused by environmental factors such as burns and bruises, is distinguished from apoptosis, and it is called necrosis. Apoptosis can be compared to the falling of the leaves, whereas necrosis is like when leaves turn brown due to the lack of water or nutrients and die. The burned or bruised area of the skin is where the cell’s necrosis occurred.
Apoptosis and necrosis are distinctively different in the process of cell death. When necrosis occurs in a cell, environmental changes increase the difference of the osmotic pressure between inside and outside of the cell. Then, the extracellular water flows inside the cell rapidly, increasing the volume of the cell and swelling the organelles. Eventually, the cell membrane bursts and dies. When this happens, the substances inside the cell are exposed and cause inflammation, damaging even surrounding cells.
Apoptosis, on the other hand, begins with the operation of specific proteins and genes hidden within cells. In other words, this occurs as the device inside the cell is triggered, and this program is written in the gene. Numerous genes are involved in programmed cell death, but the important role is played by p53 gene. The p53 gene, which in the 17th of 23 human chromosome pairs, turns on apoptosis when a cell’s DNA is severely damaged.
The cell chooses apoptosis for the whole individual. Starting from one fertilized egg, a body can be made by repeating proliferation and differentiation; and during the development and differentiation of tissues and organs, a certain number of cells are removed at a given time. The cell death that occurs to remove unnecessary parts is called programmed cell death [PCD]. For example, the tail disappears while a tadpole turns into a frog. The cells that make up the tadpole tail begin the process of apoptosis at the appropriate time as programmed in the gene. It also works this way for human fingers. Inside the womb, the hands and feet of a fetus are originally formed in a round shape. However, as the cells between the fingers and toes disappear, ten fingers and ten toes are completed.
Not only the sacrifice of pre-stored cells like the tail of a tadpole but also the phenomenon where injured cells disappear on their own is called apoptosis. When a cell is seriously damaged and has a chance to turn into a cancer cell, the cell chooses to kill itself to protect a whole. When a cell is severely modified by radiation, chemicals, or a virus, the cell operates the programmed cell death by itself before it damages the surrounding cells.
When apoptosis is in work, unlike necrosis, cells break down, DNA is cut regularly inside the nucleus, and the nucleus condenses. This is to avoid damaging the surrounding cells as much as possible during the process of death. Useful materials are stored in cell membrane pockets and transferred to surrounding cells, and the remainder is broken into smaller pieces. When the surrounding phagocytes eat away the fragmented cell fragments, the process is complete.
However, some cells that have problems with apoptosis turn into cancer cells. One unique thing about cancer cells is that they proliferate abnormally. While normal cells proliferate only to a certain level and no longer proliferate, cancer cells proliferate constantly, eating up the surrounding oxygen and nutrients. Because of this, adjacent normal cells lack nutrients, causing tissue destruction. Cancer cells kill normal cells around them, and sometimes move to other parts of the body. Cancer cells do not stop proliferating until they take an individual’s life.
When cells are cultured in the culture medium, normal cells divide up to 50 times and then die by operating apoptosis. On the other hand, cancer cells that have lost apoptosis completely proliferate without limits as long as conditions are met. HeLa, a cell line derived from cervical cancer cells taken from Henrietta Lacks who died 60 years ago, has been growing, and now an estimated 50 million metric tons of HeLa cells have been grown. Using this principle, a treatment method for inducing apoptosis by force in cancer cells through various methods such as radiation or chemotherapy to remove cancer cells that avoid apoptosis is being studied.
If the cells that have to be removed continue to exist, organs in their intact form cannot be formed. Fetuses will suffer from syndactyly wherein fingers are attached to each other, and frogs will have to live with their tadpole tails. The blood will overflow with red blood cells that have lost their function. Cancer, one of the most feared diseases of modern people, occurs when cells that were part of the body lose the apoptosis process and gradually become cancer cells. Without apoptosis, normal cells will eventually turn into cancer cells and take our lives. Aren’t we also trying to cling to the things that we need to empty out? It is time to learn the wisdom of emptying programmed in the human body.
- Reference
- Obara Hideo, Death of Everything—Life and Death to Look Back (in Japanese, 万物の死), translated by Shin Yeong-jun, Academy Books, 2008
- Park Sang-cheol, Aesthetics of Life—Life Seen by the Meaning of a Biochemist (in Korean, 생명의 미학-어느 생화학자의 뜻으로 본 생명), Tree of Thoughts, 2009
- Manfred Reitz, The Chaos Cells: Biology of Cancer (in German, Die Chaos-Zellen: Biologie der Krebserkrankung) Hirzel, S., Verlag, 2006