Life is a process from one generation to the next, so it is a process of constant renewal and constant starting from scratch. The life of a cell begins with the division of the mother cell and ends with the formation of daughter cells or the death of the cell itself. The formation of daughter cells is usually regarded as a sign of the end of a cell division, and the cell cycle refers to the process from the beginning of a cell division to the next cell division. In this process, the genetic material of the cell is copied and distributed equally to the two daughter cells.
(1) interval
The interphase is divided into three stages, namely, prophase of DNA synthesis (G 1 period), anaphase of DNA synthesis (S period) and anaphase of DNA synthesis (G2 period).
1.G 1 (the first gap) is the period from mitosis to DNA replication, also known as prophase, which mainly synthesizes RNA and ribosomes. This stage is characterized by metabolism of active substances, rapid synthesis of RNA and protein, and significant increase in cell volume. The main significance of this issue is to make material and energy preparations for the next stage of S-phase DNA replication. After cells entered G 1 phase, they did not all continue to proliferate in the next phase without exception. At this time, there may be three kinds of cells with different prospects: ① proliferating cells: these cells can enter the S phase from G 1 phase in time and maintain vigorous division ability. Such as epithelial cells of digestive tract and bone marrow cells; ② Cells that don't proliferate temporarily or static cells: These cells don't turn to S phase immediately after entering G 1 phase, and only enter S phase to continue to proliferate when necessary, such as injury or surgery. Such as hepatocytes and renal tubular epithelial cells; ③ Non-proliferative cells: After entering G 1 phase, these cells lose their ability to divide, stay in G 1 phase for life, and eventually differentiate, age and die. Such as highly differentiated nerve cells, muscle cells and mature red blood cells.
2.S phase is the period of DNA synthesis, during which histone is synthesized in addition to DNA. All the enzymes needed for DNA replication were synthesized during this period.
3. The second gap stage is the late stage of DNA synthesis and the preparation stage of mitosis. During this period, DNA synthesis stopped, and a large number of RNA and protein were synthesized, including tubulin and maturation promoting factors.
(2) the period of division
M phase: cell division phase.
Cell division period: prophase, metaphase, anaphase, anaphase.
Cell mitosis is a continuous process that needs to go through prophase, metaphase, anaphase and anaphase. A mother cell divides into two daughter cells. It usually takes 1 ~ 2 hours.
1. In the early stage, chromatin filaments were highly spiraled and chromosomes gradually formed. Chromosomes are short and thick and strongly basophilic. Two centrosomes move in opposite directions, forming two poles in the cell; Then, microtubules were synthesized from centriole satellites to form spindles. With the spiraling of chromatin, nucleoli gradually disappeared. The nuclear membrane began to decompose into discrete vesicular endoplasmic reticulum.
2. At the metaphase, the cells become spherical, and the nucleoli and nuclear membrane have completely disappeared. All chromosomes move to the equatorial plane of the cell, and the microtubules at the poles of the spindle are attached to the centromere of each chromosome. A complete genome of ***46 can be isolated from metaphase cells, of which 44 are autosomes and 2 are sex chromosomes. The karyotype of male is 44+XY and that of female is 44+XX. The isolated chromosomes are short and thick, rod-shaped or hairpin-shaped, and they are all connected by two chromatids through narrow centromeres.
3. At the later stage, due to the activity of spindle microtubules, the centromere divides vertically, and the two chromatids of each chromosome separate and move in opposite directions, approaching their centrosomes, and the chromatids are divided into two groups. At the same time, due to the activity of microfibril circulating under the cell membrane at the equator, the cells become longer and dumbbell-shaped.
4. At the end of the period, chromatids gradually uncoil, and chromatin filaments and nucleoli reappear; The vesicle combination of endoplasmic reticulum is nuclear membrane; The equatorial part of the cell narrows and deepens, and finally completely divides into two diploid daughter cells.
G0 phase: The period when cells temporarily leave the cell cycle, stop cell division and perform some biological functions.
In vivo, cells [1] can be divided into three types according to their dividing ability: ① periodic cells, such as hematopoietic stem cells, epidermal and gastrointestinal epithelial stem cells. These cells always maintain active division ability and continue to enter the cell cycle; ② terminally differentiated cells, such as mature red blood cells, nerve cells and other highly differentiated cells, have lost their ability to divide, also called terminally differentiated cells; ③ Cell groups (G0 cells) that do not proliferate temporarily, such as hepatocytes, renal tubular epithelial cells, myocardial cells and thyroid follicular epithelial cells. They are differentiated cells that perform specific functions, usually in G0 phase, so they are also called G0 phase cells. Under some stimulation, these cells re-enter the cell cycle. For example, after partial hepatectomy, the remaining hepatocytes divide rapidly.
Periodic action folding editing this paragraph
At present, scientists have found that several types of regulatory factors play an important role in the cell cycle. One is cell growth factor, which can regulate cell division and proliferation. For example, the second cell cycle regulator, also called endogenous regulator, is the protein synthesized by the cell itself.
The prelude of cell cycle regulation mechanism has been opened, and scientists are studying the relationship between cell cycle and oncogenes, tumor suppressor genes, growth factors and cell proliferation and differentiation from different angles. I believe that through hard work, we can finally find the magic "switch" to control the cell cycle. In the treatment of tumor, we can also use the principle of cell cycle to prescribe the right medicine. For example, G0 cells are insensitive to chemotherapy and often become the source of cancer recurrence in the future. Therefore, we can try to induce G0 cancer cells to enter the proliferation cycle and then kill them. This is a problem of theoretical and practical significance that is still being explored.
Related detection folding edit this paragraph
I. Sample Preparation Prepare one or more of the following samples.
One, tissue single cell suspension (such as lymph gland, spleen, bone marrow, placental cells)
B, tissue culture cells
C. Monocytes isolated from Ficoll-hypaque
Ⅱ. Reaction system-DNA hypotonic buffer
0.25g trisodium citrate
Triton-x100 0.75ml
Propidium iodide 0.025g.
0.005g ribonuclease
250 ml distilled water
After storing the hypotonic solution of DNA in a closed bottle for several months, we did not find any loss of staining activity.
III. Dye ...
1, 1× 106 cells per tube;
2. Remove the supernatant as completely as possible after the sample is centrifuged, and do not break the precipitate;
3. Add 1 ml DNA hypotonic staining buffer (which can be dyed with methyl green) to the precipitate and mix well;
4. Store the sample in the dark at 4℃ for 30 minutes or less than 1 hour for flow cytometry analysis.
Note: Prolonging the exposure time in hypotonic buffer will lead to the increase of sample fragments. Cell cycle detection can be used as an evaluation index of biocompatibility. Examples are as follows: In vitro cell culture was used to observe the effects of different mass fractions of hydroxyapatite extract on the cytological morphology of L-929 cells, MTT colorimetry was used to evaluate the effects of hydroxyapatite extract on the growth and proliferation of L-929 cells, and flow cytometry was used to detect the effects of hydroxyapatite extract on the growth cycle and apoptosis of L-929 cells. The results showed that hydroxyapatite extract had no obvious effect on the morphology of cells cultured in vitro, and had no obvious inhibitory effect on cell growth and proliferation. The cytotoxicity of extracts from different mass fractions of materials ranged from 0 ~ 1. With the increase of the mass fraction of hydroxyapatite extract, the apoptosis rate gradually increased. Hydroxyapatite extracts of 50%, 75% and 100% can obviously reduce G0 /G 1 cell ratio, increase S and G2/M cell ratio, increase DNA synthesis of L-929 cells, and promote cell growth and tissue repair. Cell cycle detection is a reliable method and index to evaluate the biocompatibility of biomaterials.
Other data folding edit this paragraph.
Cell cycle (cell mitosis) formula folding
Take plant cell mitosis as an example:
Mitosis is divided into five stages.
Connect the front, middle and back.
First, prepare the interval.
Intermittent chromatids replicate between them.
In the early stage, two things disappeared and one thing dispersed.
Centromere aggregation equatorial plate
In the later stage, silk pulls chromosomes to the poles.
Reconstruction of two-elimination and two-storage wall at the end of the period
Note: Cell walls do not form at the ends of animal cells.
Periodic detailed folding
The process from the end of one division to the end of the next division of cells that proliferate through mitosis. This process has been going on. Cell cycle is one of the important discoveries of cytology in 1950s. Before that, mitosis was regarded as the main stage in the cell proliferation cycle, while interphase cells were regarded as the static stage of cells. In 195 1, Howard et al. labeled Vicia faba root tip cells with P- phosphate and studied the time interval of DNA synthesis in root tip cells by autoradiography. It was observed that the incorporation of P was not in mitotic stage, but some time before mitosis. It was found that there was a DNA synthesis phase (S phase) in the interphase before P was mixed into DNA. There is a gap between S phase and mitotic phase (M phase) called G2 phase, and another gap between M phase and S phase called G 1 phase, and G 1 phase cannot synthesize DNA.
So they put forward the concept of cell cycle, and proved for the first time that interphase is an extremely important stage in cell cycle, and many special biochemical events related to cell division have taken place. This discovery was later confirmed by similar research conducted by scholars with H- thymidine.
Most cell life activities are spent in interphase, such as the cell cycle of rat corneal epithelial cells, accounting for 14000 minutes. The split period only takes 70 minutes. Every stage of the cell cycle has complex biochemical changes. Interphase is the period when cells synthesize DNA, RNA, protein and various enzymes, and it is the main stage to prepare the material foundation for cell division.
In a proliferating cell population, all cells do not proliferate synchronously, and they may have four fates in cell cycle operation (Figure 1): ① cells start the second cycle after M phase; ② Stop at G2 phase, which is called G2 phase cell (R2), and can enter the circulation after being stimulated; ③ It stops at G 1 phase and is called resting cell or G0 phase cell. These cells can still enter the circulation and start DNA synthesis and mitosis after some stimulation. ④ Cells that lose vitality and are close to death are called lost cells or cells that no longer divide. Cells that continue to divide move from one mitotic stage to the next along the cell cycle. Cells that no longer divide leave the cell cycle, no longer divide, and eventually die.
G 1 is the period of synthesizing a large number of substances. The cell volume gradually increases, which makes RNA (including tRNA, mRNA, rRNA and ribosome, etc. ). RNA synthesis leads to the formation of structural proteins and enzyme proteins, which in turn controls the metabolic activities of forming new cell components. G 1 can be divided into two stages: early G 1 and late G 1. In the prophase of G 1, the cells synthesized various RNA and protein peculiar to G 1, but in the anaphase of G 1 to S, they converted into some precursors and enzyme molecules needed for DNA replication, including thymine kinase, thymine nucleotide kinase and deoxythymine nucleotide synthetase. In particular, DNA polymerase has increased dramatically. The increase of these enzyme activities is an indispensable condition for making full use of nucleic acid substrates to synthesize S-phase DNA.
The duration of G 1 phase is quite different, and most cells have a long G 1 phase, which is related to the need to increase cell quality. However, there is no G 1 phase in some cells of unicellular organisms such as amoeba and Tetrahymena (such as sea urchin embryo and mouse embryo cell), and there is no G 1 and G2 phase in China hamster ovary mutant, which connects M phase with S phase. The reason why the length of G 1 period changes greatly is related to the existence of a correction point or blocking point (R point for short) in G 1 period. The r point mainly controls the length of G 1 period. Through this, cells can complete other stages of the cell cycle at a normal speed without being affected by external conditions. Therefore, some people think that the growth of cells stops at the r point of G 1 period. For example, when the level of cAMP in cells increases and the cell density increases, the transition from G 1 phase to S phase can be prevented, puromycin can inhibit protein synthesis or radiomycin D can inhibit RNA synthesis, which can also delay the transition from G 1 phase to S phase. It has been found that trigger protein can be synthesized in G 1 phase; It is unstable and easy to decompose, so it is called V protein. When V protein reaches a certain level in G 1 cell, the cell can enter S phase through R point.
The regulation of cell cycle in G0 phase is mainly realized by the retention of G 1 phase, that is to say, cells are in a retention state. Cells are divided into two through M phase, some can continue to divide and cycle, and some can turn into G0 phase. G0 phase is a period of breaking away from the cell cycle and temporarily stopping division. However, under certain suitable stimulation, it can enter the circulation (Figure 1), synthesize DNA and divide. The characteristics of G0 phase are as follows: ① In unstimulated G0 cells, the potential of DNA synthesis and cell division still exists; ② When G0 cells are stimulated to proliferate, they can synthesize DNA and divide.
In S phase, DNA synthesis and histones related to DNA assembly and chromatin are completed. During this period, the DNA content doubled. At the end of S phase, each chromosome replicates into two chromatids (Hole, 1979). The structures of the two generated sub-DNA molecules are exactly the same as those of the original DNA molecules. A person's nuclear diameter is 10 ~ 20 microns, in which the DNA content is 10g. If it is pulled into a DNA chain, the length can reach 3 meters. The S phase of mammalian cells is generally 6-8 hours. The replication of DNA can be completed in a few hours, mainly because the DNA chain is divided into many replication units (replicators) (up to about 10000), which can be replicated at different times in S phase. In addition, there is S-phase histone synthesis-between G1-S phase, the histone gene is activated, and the transcription of histone mRNA is increased, which runs through the whole S phase. The synthesized histone rapidly transforms the newly synthesized DNA into a nuclear histone complex.
S phase cells contain a factor that can induce DNA synthesis. The cell fusion experiment showed that G 1 cells could accelerate the initiation of DNA replication in their nuclei after being fused with S-phase cells. The base composition of DNA replicated in different stages of S phase is different. Pre-replicated DNA is rich in G-C bases, while post-replicated DNA is rich in A-T bases, that is, euchromatin replicates earlier than heterochromatin (Figure 2).
G2 phase is the gap between the end of DNA replication and the beginning of mitosis, during which cells synthesize some protein and RNA molecules, providing material conditions for entering mitosis. The tracing of radiolabeled RNA precursors and protein precursors showed that there was strong synthesis of RNA and protein in G2 phase. If these synthetic processes are disrupted, cells cannot transition to M phase. G2 phase synthesizes the components needed for chromosome concentration and mitotic apparatus formation. Some people think that G2 phase continues to complete the synthesis of tubulin from S phase, which provides raw materials for the assembly of M phase spindle filaments. Mitotic factors are synthesized in the late G2 phase. In some cells lacking G 1 phase, G2 phase is more complicated, and it has to undertake the events that other cells need to complete in G 1 phase. In a few cases, mitosis begins immediately after the end of S phase, but there is no G2 phase.
M mitosis is a period in which the morphological structure of cells changes rapidly, including a series of changes in the nucleus, the concentration of chromatin, the appearance of spindles, and the accurate and equal distribution of chromosomes to two daughter cells, so that the divided cells maintain genetic consistency. M stage is divided into prophase, metaphase, anaphase and anaphase (see mitosis). Although M phase is the most significant phase of morphological changes, its respiration is reduced, protein synthesis is obviously reduced, and metabolic turnover such as RNA synthesis stops, because the energy required for mitosis is related to the synthesis and storage of other basic substances in interphase.
During the cell cycle, a series of changes have taken place in cell morphology. From the light microscope, it can be seen that the cells in G 1 phase are the smallest, flat and smooth, and gradually increase with the development to S→G2→M phase, from flat to spherical. Under the scanning electron microscope, we can clearly see the changes of cell surface morphology in different periods, such as the gradual increase of microvilli, which is related to various biochemical and physiological periodic changes in cells.
Many biochemical events in cell cycle are regulated in a certain order, which is closely related to the expression of genes in a certain order.
Some people think that there are two most important stages in the cell cycle: G 1 to S and G2 to M; These two stages are in a period of complex and active changes at the molecular level, which are easily affected by environmental conditions. If they can be artificially regulated, it will be of great significance to deeply understand the growth and development of organisms and control the growth of tumors.
It has been found that many internal factors can stimulate or inhibit cell proliferation, such as hormones, serum factors, polyamines, proteolytic enzymes, neuraminidase, cAMP, cGMP, diglyceride (DG), inositol triphosphate (1P3), Ca messenger system and so on. The increase of intracellular cAMP concentration can inhibit cell proliferation, and all factors that can increase intracellular cAMP can inhibit cell proliferation and slow down cell growth. On the contrary, all factors that can reduce the content of cAMP in cells can promote DNA synthesis and cell proliferation. The content of cAMP in different stages of cell cycle is also different (see table). In China hamster ovary strain, the content of cAMP in M phase was the lowest, and the level of cAMP increased three times after M phase. From the prophase of G 1 to the anaphase of G 1, the level of cAMP decreased to a moderate level, and remained low until S (Figure 3).
Many experiments have shown that cGMP can also regulate cell proliferation. If cGMP or bisbutyryl cGMP is added to 3T3 cells in G 1 phase, the DNA content can be induced to increase and the cell division can be promoted. If the level of cGMP in cells is increased, the mitosis of cells can be promoted, and conversely, drugs that promote mitosis can also increase the concentration of cGMP.
CAMP can inhibit cell division and promote cell differentiation, while cGMP can inhibit cell differentiation and promote cell proliferation. In normal growing cells, cAMP and cGMP are maintained at an appropriate level to regulate and control the operation of cell cycle.
Somatostatin is a small molecule protein or polypeptide produced by cells, some of which also contain sugar or RNA. It is not species-specific, but cell-specific. It can inhibit the proliferation of similar cells and is reversible. When the somatostatin content reaches a certain concentration, it can inhibit the proliferation of similar cells, while when the somatostatin concentration decreases, the cell proliferation is active. Some people think that the mechanism of somatostatin is that it can activate adenosine cyclase activity on cell membrane and increase the concentration of cAMP in cells, thus inhibiting cell proliferation. It is also possible that camp-dependent protein kinase phosphorylates protein to affect the activity of regulatory genes.
Cell cycle is also influenced by the body's regulatory system. For example, liver regeneration is accelerated by the regulatory system. However, because the host is out of control, tumor cells proliferate viciously. The principle of cell cycle can be applied to tumor treatment. For example, G0 cells are insensitive to chemotherapy and often become the source of cancer recurrence in the future. Therefore, by studying the regulatory mechanism, inducing G0 cancer cells to enter the cell cycle, and then reasonably killing them with anticancer drugs is an important regulatory measure to prevent cancer metastasis and spread, and it is also a research problem with theoretical and practical significance in cell dynamics.
In a word, the molecular basis of cell proliferation regulation is still less, which needs further exploration.
Bacterial DNA value-added characteristic folding
Bacterial DNA replication, RNA transcription and protein synthesis are carried out at the same time, which is the adaptation of bacteria to rapid growth.
DNA replication is not limited by cell cycle. When the last cell division ends, the DNA in the cell is copied to the middle to ensure the rapid progress of the next division.