Cell cycle and apoptosis
After we have dealt with the basics of genetics in the last articles, the importance and scope of genetics in the overall construct of the cell must now not be missed. Further information about emergency programs of the cell, which can be initiated, among other things, in the case of defective DNA, is tangential to the topic of genetics. Finally, we look at very specific genes that can have serious consequences in the event of mutations.
Brevity is the spice of life: Cell cycle and apoptosis summarized for you !
- Our body cells go through a cell division cycle. However, not all cells are in this cycle. Most cells perform their function in the arrest phase.
- The cell cycle is divided into interphase and mitotic phase. The interphase is divided into three sections, which are characterized by protein and fat synthesis, growth, DNA duplication, and nuclear protein formation. Mitosis is characterized by the division of cell contents into two new cells.
- The entire cell cycle is monitored by special enzymes and checkpoints to avoid potential errors. Mutations in the defense systems lead to momentous consequences.
- In the worst case, a cell arrested in the cell cycle is sent into programmed cell death.
- Defensive systems must function optimally — each individual can contribute to this through optimal lifestyle conditions.
Not every cell is in an active cell cycle
To understand how our cells work and how our biological system works as a whole, let’s first turn our attention to the cell cycle. Not every cell is in an active cycle in our body. Most cells in our body perform their function as differentiated cells and are in a so-called G0 phase. Simplified, this means that these cells are not dividing or multiplying. By the way — most cells in our body remain in the G0 phase. Only special cells are subject to continuous cell division and are thus in an active cell cycle. For cells in the G0 phase, it takes impulses, for example in the form of an injury and the associated cell death, to re-enter a cell division cycle.
The cell cycle goes through several phases
Ultimately, the cell division cycle consists of an interphase and a mitotic phase. The first phase (interphase) is divided into three sections (G1, S, and G2 phases). In the G1 phase, the cell provides increased protein and fat synthesis and growth. The S phase is characterized by DNA duplication and nuclear protein formation. Last, the G2 phase is devoted to proper division of the cell and checking the duplicated genetic information for errors. After completion of interphase, the cell proceeds to mitosis. Here, the genetic information and the remaining contents of the cell are distributed to two new cells and finally divided in the middle.
The interphase and mitosis phases are strictly controlled
Each cell has a variety of enzymes that control the progression of the cell cycle at specific times and allow it to “slide on” to the next phase of the cycle. Simplified, you can think of checking like a pit stop. The cell cycle is stopped at each of these stops and, in particular, the genetic information is checked for errors. If mutations occur in these cell cycle control units, there is a potential risk of uncontrolled proliferation of incorrect genetic information. In this context, the protein p53 plays a central role in preventing the transmission and propagation of incorrect genetic information. This protein is also known as the “guardian of the genome”. If mutations occur in the gene for this protein, this has dangerous and momentous consequences for affected individuals.
The cell can defend itself with apoptosis
If DNA damage, i.e. mutations, occur during the cell cycle, the cell first tries to reverse the deviations from the norm and eliminate them by means of various repair mechanisms. However, if the repairs are unsuccessful, advancing to the next stage of the cell cycle fails with intact cycle controls. One of the following steps could be the initiation of so-called apoptosis. Translated, this process can be called “programmed cell death”, whereby the cell is degraded in a controlled manner without further side consequence. In this process, the already mentioned guardian of the genome plays a significant role. The aim is to prevent faulty genetic information from multiplying.
The biological sequence shows: there are many potential hazards for our DNA
In summary, many potential sources of error occur during the life cycle of a cell. Some of these errors can be reversed by established checkpoints and special systems. However, these systems must always work. In the worst case, the cell must be sent into apoptosis by internal signals. But again, the facilities necessary for this must function optimally to avoid consequences. The lifestyle of each individual can contribute to a proper cell cycle.
Text-Sources:
(1) Horn, Biochemie des Menschen, 7. Auflage, 2018
(2) Plattner und Hentschel, Zellbiologie, 5. Auflage, 2017
(3) Koolman und Röhm, Taschenatlas Biochemie des Menschen, 5. Auflage, 2019
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