Apoptosis is the phenomenon of programmed cell death, followed by a set of characteristic cytological features (markers of apoptosis) and the molecular processes that are different in unicellular and multicellular organisms. So, apoptosis is a form of cell death, manifested by a decrease in its size, condensation and fragmentation of chromatin, compaction of the outer and cytoplasmic membranes without exiting the cell contents into the environment (Pereira 401).
It was suggested to distinguish two types of cell death: apoptosis and necrosis. The fundamental difference is that in necrosis is the result of an unplanned event and occurs spontaneously, while apoptosis is a well-regulated process of cell elimination. Necrosis develops when there are external to the cell damaging agents, and inadequate environmental conditions (the extreme level of pH, hyperthermia, and mechanical effects, the action of agents that damage the membrane, forming pores in the membrane with the participation of complement factors).
There are four stages of apoptosis:
– Implementation of the program;
– Removal of dead cells (Potten 96).
There is a great significance of apoptosis. Apoptosis is a genetically programmed defense mechanism, which aims to launch self-destruction of abnormal, mutated cells (which contain defective DNA), in order to preserve the integrity of the microorganism. As a rule, the fight against defective cells is not limited to the launch of apoptosis, and activation occurs at the cellular and humoral immunity. The insufficiency of apoptosis is shown through the uncontrolled division of abnormal cells, ie the formation and growth of the tumor. At the same time, increased apoptosis can lead to premature aging, the development of cell aplasia and degeneration. Currently, while the development of modern methods of anticancer therapy much attention is paid to the processes of cell regulation and induction of apoptosis.
Apoptosis is very important for immunity system.Since the 1990’s apoptosis has been studied extensively as it became clear that violations of apoptosis lead to various diseases. Thus, the lack of apoptosis leads to cancer and other tumors, an excess of apoptosis leads to loss of cells, such as in neurodegenerative processes.
Apoptosis occurs if a cell is infected with a virus or is too badly damaged by aggressive chemical agents or ionizing radiation (eg X-rays). The decision on cell apoptosis can be taken only by the cell itself, neighboring cells or immune cells. If the cell fails to produce apoptosis due to mutation or infection, it can begin to share uncontrollably, leading to the tumor. Thus, the human papillomavirus uses its gene E6 to destroy the protein p53, critically important for apoptosis. As a result, the virus causes cervical cancer, so it is oncovirus.
Apoptosis is important for immunity: T-cells maturing in the thymus are tested for the ability to recognize foreign antigen. Those of them that are not able to do it (which is about 97% of all newly mature cells) are sentenced to apoptosis. Apoptosis plays an important role in maintaining homeostasis. Daily in a healthy person there appear 50-70 billion of new cells, and the same number of them dies, mostly due to apoptosis (Pereira 404). During one year there are renewed as many cells that their total weight is equal to the weight of the body.
In contrast to necrosis, in which cells swell and burst, releasing their contents (potentially harmful) in the extracellular space, in apoptosis the cells shrink and are often divided into parts. As a result, the remnants of cells can be absorbed (by phagocytosis) by neighboring cells or macrophages. Apoptosis plays an important role in embryonic development and morphogenesis of animals and plants. For example, separation of fingers in the embryo requires the cells located between the fingers to be destroyed (Jacobson 201).
The role of apoptosis in defense against cancer is also increadable. Modern chemotherapy of tumors is often based on amplification of apoptosis in cancer cells based on the fact that they are more sensitive to it than the normal non-cancerous cells. Unfortunately, in advanced stages of tumor, apoptosis in cancer cells is usually suppressed. Some interferons enhance the expression of the gene p53, helping the apoptosis. As a result, these interferons help to fight cancer. As it was written above, apoptosis is a necessary phenomenon for human organism that helps to renew it.