The entire cell cycle is controlled by a control system. On one Cell cycle checkpoint critical processes and phase transitions that take place within a cell cycle are regulated.
What is the cell cycle checkpoint?
The sequence of physiological events in cells that have a nucleus is called the cell cycle. This takes place as a cycle that begins after one cell division and initiates the next. It consists of the interphase and mitosis. A mother cell divides into two daughter cells, in which the interphase begins. The gene activity there regulates the metabolism of the growing cell, while a nucleolus develops in the cell nucleus.
The interphase is the longer of the two and then switches to mitosis. It is in turn divided into different phases. These are the G1 phase in which the cell grows and the duplication of chromosomes is prepared, the S phase in which the chromosomes double and the G2 phase in which the cell continues to grow and the next mitosis is prepared.
This entire cycle is controlled by a molecular control system. This is where cell events are triggered and controlled, which convey stop and further signals in the form of control points. Critical processes and phase transitions that take place within the cell cycle are analyzed at a control point. These serve as protection for the integrity of the genetic material and ensure that the cell does not degenerate.
A critical process can e.g. B. be when a separation of the chromosomes occurs in the metaphase. The metaphase represents the second phase of cell division, known as mitosis and meiosis. In the metaphase, the nucleolus and nuclear envelope recede. A typical structure is formed, a so-called monaster. The chromosomes differ significantly from each other in this phase.
Function & task
Cell cycle checkpoints are set in two phases. These are the interphase with the control points G1 and G2, and the mitosis phase. During the first, there is increased core activity, which is associated with an increased risk of DNA damage from cancerous pathogens, for example caused by UV light. This in turn can lead to malignant tumors.
Various toxins, drugs, environmental poisons and toxins can also cause diseases here. In the interphase, specialized proteins are built up that counteract such defects, detect them and, at the checkpoint, prevent the cell from switching to another phase. Cell death is then brought about by apoptosis. Figuratively speaking, one can speak of a controlled suicide of the cell, compared to the death of the cell by e.g. B. mechanical injuries trigger an inflammatory reaction and no cytoplasm is released.
At this control point it is decided whether the cell is to be divided or not. Most cells in the human body are in a state that the cell no longer divides. So if there is no further signal at this control point, the cell has left the cycle and is no longer dividing. It then changes to the G0 phase.
Molecular control mechanisms take place in cell cycle control. In the interphase, these are the formation of proteins 53 and 21 and BAX. The protein 53 is decisive for the control of the DNA integrity. He is also known as the “guardian” of the genome. In a biological process in which the genetic information of a DNA strand is transferred to the RNA, the protein acts as a transcription factor that upregulates the DNA in the event of damage and causes the expression of tumor suppressor genes.
Protein 21 is also essential for the cell cycle of vertebrates, a so-called CDK inhibitor, which blocks the cell at the phase transitions so that the enzymes for DNA repair have enough time to, for example, suppress the growth of cancer cells or cause various genetic defects remedy. BAX, in turn, is a protein that acts as a cofactor for protein 53. It monitors the apoptosis of the cell.
At the second cell cycle checkpoint, in the mitotic phase, the chromosomes are separated in the metaphase. This is always a critical moment as e.g. B. incomplete separation leads to somatic numerical chromosome aberrations.
It is known that the human body cell has 46 chromosomes. This condition is called euploidy. When an abnormality forms, the chromosomes can multiply. Then we speak of polyploidy. Human life is not possible under these conditions. If the number of chromosomes does not correspond to the haploid set (n = 23), there is a faulty separation of the chromosomes or sister chromatids. One disease that is associated with this is trisomy 21.
In the mitosis phase, the correct distribution of the chromosomes between mother and daughter cells is ensured. Hence, the mitotic phase is a spindle control point. This brings with it a spindle control mechanism based on the fact that the chromosomes are only separated when the microtubules are correctly attached to the kinetochores. The exact process during the mitosis phase has not yet been precisely researched. Doctors assume that the proteins interact with the kinetochore and the adhering microtubules of the spindle apparatus.
Illnesses & ailments
If the cell cycle checkpoints are disturbed, z. B. form cancer cells. The cancer cell is created by transforming a normal cell into an abnormal one. In the healthy immune system, a cell is recognized and destroyed. If this does not happen, a tumor forms.
If the cell remains in its original location, it is called a benign tumor. This can be eliminated. The cells of a malignant tumor, on the other hand, are able to damage other organs and cells, can disrupt the metabolism and form metastases. In contrast to normal cells, cancer cells can divide infinitely often and are therefore difficult to treat.
