Significance: Cell proliferation is one of the important physiological functions of living cells and the important role of organisms Vital characteristics 。 Cell proliferation is the basis of organism growth, development, reproduction and heredity. Method: Eukaryote According to different processes, there are three ways to split mitosis ， Amitosis ， Meiosis 。 Among them, mitosis is the most common mode of division in all eukaryotes such as humans, animals, plants, fungi, etc Eukaryotic cell The main way of proliferation. Meiosis is germ cell A special mitosis in formation. Split Introduction
mitosis yes Eukaryote The main way of cell division. (The figure at the upper right corner shows the beginning and result of common mitosis) multicellular organism The body increases the number of somatic cells by mitosis. somatic cell Mitosis is carried out periodically, that is, with cell cycle 。 Cell cycle A cell cycle refers to a cell that divides continuously from the completion of one division to the completion of the next.
A cell cycle consists of two stages: Interphase and Fission period 。 From the end of a cell division to the next division, it is an interphase. After the end of the interdivision period, it enters the division period. In a cell cycle, the time occupied by these two stages is quite different. Generally, the interphase occupies 90% to 95% of the cell cycle; The division phase accounts for about 5% to 10% of the cell cycle. Different types of cells, one cell cycle The time is also different. Cell division interval The interphase of cell division is the beginning of a new cell cycle, which prepares the conditions for cell division. Very complex changes are taking place inside the cell. In recent years, radioactive isotope Mark the certificate of autoradiography technology, interval The biggest characteristic of cells is to complete DNA molecule The replication and synthesis of related proteins. Therefore, the interval is the whole cell cycle The critical preparation stage in. · mitosis Periodic change of cell division The most obvious change is the change of chromosomes in the nucleus. For the convenience of research, people Fission period It is divided into four periods: early stage, middle stage, late stage and late stage. In fact, changes in various periods of the split period are continuous, and there is no strict time limit. early stage
In the prophase of cell division, the most obvious change is the appearance of chromosomes in the nucleus. Interphase The duplicated chromosomes are gradually shortened and thickened due to the spiral entanglement, and the shape is clearer and clearer. stay optical microscope When we look at the cells in this period, we can see that each chromosome actually includes two parallel chromosomes Sister chromatid These two parallel sister chromatids are not completely separated, but connected by a common centromere. In the early stage, nucleolus Gradually disintegrate, and the nuclear membrane gradually disappears. At the same time, a lot of Spindle yarn , forming a fusiform Spindle The chromosomes in the cell are scattered in the center of the spindle. metaphase
At the metaphase of cell division, the spindle is clearly visible. At this time Centromere On both sides of the cell, there are spindle filaments attached to it. The spindle filaments pull chromosomes to move, so that the centromere of each chromosome is arranged on a plane in the center of the cell. This plane is perpendicular to the axis of the spindle, similar to the position of the equator on the earth, so it is called Equatorial plate 。 In metaphase cells, the shape of chromosomes is relatively fixed, the number is relatively clear, and it is easy to observe clearly. later stage
At the later stage of cell division, each centromere splits into two, the two originally connected to the same centromere Sister chromatid With the separation, they become two sub chromosomes. Spindle yarn Towing Daughter chromosome Respectively to the two poles of the cell, so that each pole of the cell has a set of chromosomes. The shape and number of these two sets of chromosomes are identical, and each set of chromosomes is identical to the shape and number of chromosomes in the parent cells before division. late
When these two sets of chromosomes reach the two poles of the cell, the shape of each chromosome changes and gradually becomes a slender and coiled silk. At the same time, the spindle filament gradually disappeared, and new nuclear membranes and nucleolus 。 The nuclear membrane surrounds the chromosome and forms two new nuclei. At this time Equatorial plate A Cell plate The cell plate expands from the center of the cell to the periphery, gradually forming a new cell wall 。 Finally, one cell divides into two daughter cells. Most of the daughter cells go to the next cell cycle Of Interphase Status. Animal cell mitosis And plant cell Are basically the same. The different characteristics are: first, animal cells have Centrosome , on cell division Of interval , two of the centrosome Centriole Each produces a new centriole, so there are two groups of centrioles in the cell. In the process of cell division, the position of one group of centrioles remains unchanged, and the other group of centrioles moves to the other pole of the cell. Around these two groups of centrioles, numerous radial Star ray The star rays between the two sets of centrioles form Spindle 。 Second, at the end of animal cell division, the middle part of the cell does not form Cell plate Instead, the cell membrane sinks inward from the middle of the cell, and finally constricts the cell into two parts, each containing a nucleus. In this way, one cell divides into two daughter cells. Cell mitosis The important significance of the is to accurately distribute the chromosomes of the parent cells to the two daughter cells after replication. Because there are genetic material Therefore, in the biological parent and Progeny It maintains the stability of genetic traits. Visible, cellular mitosis It is of great significance for biological heredity. 
Schematic diagram of animal cell mitosis Cells Amitosis The process of nuclear constriction is relatively simple. Generally, the nucleus extends first, enters from the middle of the nucleus, and constricts into two nuclei; Then, the whole cell constricted into two parts from the middle to form two daughter cells. Because it didn't appear in the process of splitting Spindle yarn And chromosomes, so it is called amitosis. (such as red blood cells of frogs) It's a special way mitosis , it has Sexual reproduction Cell formation. It is a sexual reproduction organism germ cell (e.g. animal Spermatogonia or Oogonia ）Develop into mature germ cells（ sperm or Egg cell ）The process of meiosis. During the whole process of meiosis, chromosomes are duplicated only once, and cells divide twice in succession. The result of meiosis is that the number of chromosomes in the newly generated germ cells is half that of the newly original germ cells. For example, human spermatogonia and oocytes each have 46 chromosomes, while sperm and oocytes formed through meiosis only contain 23 chromosomes. Bacteria can be asexual or Genetic recombination There are two ways of reproduction, the main way is to Dichotomy such Asexual reproduction Method of: one Bacterial cell wall Transverse split to form two Progeny Cells. Besides bacteria, dichotomy is also protozoan The most common one Asexual reproduction . Generally mitosis During division, the nucleus is divided into two by one, chromosomes are equally distributed in the two daughter nuclei, and then the cytoplasm also surrounds the two nuclei, forming two daughter bodies of equal size and shape. The two division can be longitudinal, such as Euglena; It can also be transverse split, such as paramecium; Or oblique division, such as hornwort. No bacteria nuclear membrane , only one large ring DNA molecule When bacterial cells divide, The DNA molecule attaches to the cell membrane and replicates into two, then with the extension of the cell membrane, the two copied DNA molecules are separated from each other; At the same time, the cell membrane and cell wall in the middle of the cell grow inward to form a diaphragm, which divides the cytoplasm into two halves and forms two sub cells. This process is called bacterial Dichotomy 。 Amitosis is the earliest one Eukaryotic cell The splitting mode of Eukaryote Ubiquitous in, and not only in somatic cell In, even in germ cell Both can undergo amitosis. Because of its Mitosis No chromosome and Spindle yarn ， Cytokinesis The later genetic material may not be evenly distributed to Daughter cell , and mitosis They are very different, so they are called amitosis. The process of amitosis can be roughly divided into four stages: the first stage in the nucleus Chromatin Replication multiplication, nuclear and nucleolus Increased volume, nucleolus and nucleolus Organization Center Split. In the second phase, nucleolus and nucleolar tissue center are used as the division braking center nuclear membrane Perichromatin associated Chromatin filament It is a traction belt, which pulls the newly copied chromatin and the original chromatin respectively. The newly copied chromatin leaves the nuclear membrane and moves to the equatorial surface of the nucleus under the traction of chromatin filaments from the tissue center of the opposite nucleolus. In the third stage, the nucleus grows into a dumbbell shape, and the central part shrinks and becomes thin. In the fourth stage, the nuclear membrane invagination deepened and finally constricted into two complete daughter nuclei; Then, the whole cell constricted into two parts from the middle to form two daughter cells. It is easy to see that: Amitosis and Dichotomy There are essential differences. Dichotomy refers to prokaryote It is the most primitive way of cell proliferation, and amitosis is Eukaryote Unique cell proliferation mode, through this division, multiple nuclei can be formed at the same time; The nucleus can still perform its physiological function during division. There are many research methods for cell proliferation, mainly including BrdU, EdU, CCK8, etc. Among them, EdU detection method is the latest cell proliferation detection method.
EdU is a Thymidine Analogue, which can substitute T to infiltrate the replicating DNA molecule during cell proliferation ® Fluorescent dye Specific reaction test of DNA replication The activity can accurately reflect the proliferation of cells by detecting EdU markers. Compared with BrdU detection method, EdU detection method is faster, more sensitive and more accurate. EdU detection dye is only 1/500 of the size of BrdU antibody, which is easy to diffuse in cells, without DNA denaturation （ Acidolysis 、 pyrolysis , enzymolysis, etc.) can effectively detect, effectively avoid sample damage, and more accurately reflect cell proliferation and other phenomena at the cell and tissue levels. 
