Apoptosis

Apoptosis is a basic life phenomenon that exists widely in the biological world. It plays an important role in cell growth, development and proliferation. It is currently believed that extracellular stimuli that induce apoptosis must pass through a series of signal transmissions within the cell, which is one of the important markers for DNA-selective cleavage between nucleosomes. The term was first introduced in the 1970s to refer to a single cell mild death form controlled by genes under physiological or certain pathological conditions. In the process of occurrence and development of multicellular organisms, in order to maintain normal physiological functions, some cells undergo spontaneous cell death, which is regulated by a series of related molecules in the cell, accompanied by typical morphological changes. This phenomenon is called apoptosis. Apoptosis refers to the process in which a cell automatically ends its life under the control of an intrinsic genetic mechanism under certain physiological or pathological conditions. And programmed cell death (PCD) refers to the reactive death of a certain physiological stimulus during development, which requires certain gene expression. Apoptosis is a description of the morphological changes in a series of fixed patterns during cell death, while PCD is a functionally focused concept. There are differences between the two, but they are often mixed. Apoptosis (ap. Ptosis) or programmed cell death (PCD) is a cellular death process in which multicellular organisms regulate the development of the body and maintain the stability of the Pb gene. At present, there are various names for spontaneous degeneration of cells. More commonly used is programmed cell death (Pr08Nmmed celld6ath, PcD), originally used for embryonic development. The spontaneous degeneration of cells in specific parts during embryonic differentiation is caused by the expression of intracellular genes in this part according to certain procedures, also known as gene-scheduled cell death, physiological cell death, naturally occurring cell death, cell sequestration, apoptosis. Or apoptosis, etc. Apoptosis is characterized by nucleus condensation, chromosomal DNA being cut into ladders by nucleosomes, cell shrinkage, and finally formation of apoptotic bodies. Does not cause the dissolution of surrounding cells. Apoptosis is emitted in the cell population, progresses in stages, and depends on the supply of ATP and the synthesis of RNA and protein, which is an active elimination mechanism. It can be observed not only in the physiological state such as individual development and egg cell retreat, but also in many diseases and pathological conditions such as autoimmune diseases, neurodegenerative diseases, and ischemic diseases. The intracellular signaling pathway of apoptosis can be roughly divided into two phases, an induction phase and an implementation phase. Factors inducing apoptosis during the induction phase of apoptosis are endogenous and exogenous. Endogenous factors include the activation and inhibition mechanisms of apoptosis-inducing mechanisms (such as Fas ligand, tumor necrosis factor, etc.) (inhibition of growth factors, hormones, receptor factors and other proliferative factors). Exogenous factors include physical factors such as radiation and heat shock, chemical factors such as drugs and poisons, and biological factors such as viruses and bacteria. In recent years, it has also been found that the effects of reactive oxygen species and nitric oxide on nervous system diseases, cardiovascular diseases, immune diseases and aging are related to apoptosis to varying degrees. Recent studies have shown that the key link in the occurrence of apoptosis is not in the nucleus but in the cytoplasm. The mitochondrial membrane function changes, the intimal transmembrane potential disappears and the release of protease activators in the mitochondria induces various apoptosis-related metabolic changes before apoptotic cells are induced to undergo characteristic morphological changes and DNA degradation. Biological functions of apoptosis (1) Elimination of unwanted or redundant cells, the human brain has 95% of cell death during development. (2) Remove cells that are no longer functioning. The tail cells die when the sputum is abnormal; the mammalian endometrial epithelial cells die during the menstrual period. (3) Remove abnormally developed cells. As the development of the vertebrate visual system, neurons that do not form the correct neuronal connections are removed. (4) Some harmful cells are removed, and thymocytes are induced to die before leaving the thymus. The process of apoptosis The process of apoptosis can be roughly divided into four stages: (1) Apoptosis signal transduction When the apoptosis-inducing factors inside and outside the cell bind to the affected cell receptor, the cells produce complex biochemical reactions. And form a second messenger related to apoptosis: cAMP, Ca2+, ceramide and other signaling molecules form a death signal. (2) The apoptotic gene regulated by apoptotic gene activation starts to follow a predetermined program after receiving the death signal, and synthesizes various enzymes and related substances required for performing apoptosis. (3) Execution of apoptosis (common pathway) The main performers of apoptosis are two types of enzymes: endogenous nuclease (Dnase) - a biological command system that completely destroys cells; Caspases 3 - a complete disintegration of cells. (4) Clearance of apoptotic cells After apoptosis, cells can be decomposed by adjacent macrophages.