what are the three phases of cell division
G1 phase


The g phase, or Gap 1 phase, is the first of four phases of the cell cycle that takes place in eukaryotic cell division. In this part of interphase, the cell synthesizes mRNA and proteins in preparation for subsequent steps leading to mitosis. G phase ends when the cell moves into the S phase of interphase. G phase together with the S phase and G phase comprise the long growth period of the cell cycle called interphase that takes place before cell division in mitosis (M phase). During G phase,
729024
Mitosis


not always occur; coenocytic (a type of multinucleate condition) cells undergo mitosis without cytokinesis. The mitotic phase is a relatively short period of the cell cycle. It alternates with the much longer "interphase", where the cell prepares itself for the process of cell division. Interphase is divided into three phases: G (first gap), S (synthesis), and G (second gap). During all three parts of interphase, the cell grows by producing proteins and cytoplasmic organelles. However, chromosomes are replicated
104209
Plant embryogenesis


from a single pollen grain. Pollen grains consists of three cells - one vegetative cell containg two generative cells. According to Maraschin et al., androgenesis must be triggered during the asymmetric division of microspores. However, once the vegetative cell starts to make starch and proteins, androgenesis can no longer occur. Maraschin et al., indicates that this mode of embryogenesis consists of three phases. The first phase is the "acquisition of embryonic potential", which is the repression of gametophyte formation, so that the differentiation of cells
4866836
Cell cycle


division again. It is also called preparatory phase or intermitosis. Typically interphase lasts for at least 91% of the total time required for the cell cycle. Interphase proceeds in three stages, G, S, and G, followed by the cycle of mitosis and cytokinesis. The cell's nuclear DNA contents are duplicated during S phase. The first phase within interphase, from the end of the previous M phase until the beginning of DNA synthesis, is called G (G indicating "gap"). It is also called
7478760
KaiC


of "Synechococcus" are linked together through a one way mechanism. The circadian clock gates cells division, only allowing it to proceed at certain phases. The cell cycle does not appear to have any effect on the circadian clock though. When binary fission occurs, the daughter cells inherit the mother cell's circadian clock and are in phase with the mother cell. The circadian gating of cell division may be a protective feature to prevent division at a vulnerable phase. Phases in which KaiC has high ATPase activity do not allow for
17909113
Schizosaccharomyces pombe


mitosis, division occurs by the formation of a septum, or cell plate, that cleaves the cell at its midpoint. The central events of cell reproduction are chromosome duplication, which takes place in S (Synthetic) phase, followed by chromosome segregation and nuclear division (mitosis) and cell division (cytokinesis), which are collectively called M (Mitotic) phase. G1 is the gap between M and S phases, and G2 is the gap between S and M phases. In the budding yeast, the G1 phase is
13946571
Cell division


and more cyclin dependent kinases attach to cyclin signaling the cell further into interphase. At the peak of the cyclin attached to the cyclin dependent kinases this system pushes the cell out of interphase and into the M phase, where mitosis, meiosis, and cytokinesis occur. There are three transition checkpoints the cell goes through before entering the M phase. The most important being the G-S transition checkpoint. If the cell does not pass this checkpoint, then the cell will exit the cell cycle. Prophase is the first stage of
16324801
Cell division


the process a cell must go through before mitosis, meiosis, and cytokinesis. Interphase consists of three main phases: G, S, and G. G is a time of growth for the cell where specialized cellular functions occur in order to prepare the cell for DNA Replication. There are checkpoints during interphase that allow the cell to be either advance or halt further development. In S phase, the chromosomes are replicated in order for the genetic content to be maintained. During G, the cell undergoes the final stages of growth before
16324799
Cell cycle


have temporarily or reversibly stopped dividing are said to have entered a state of quiescence called G phase. After cell division, each of the daughter cells begin the interphase of a new cycle. Although the various stages of interphase are not usually morphologically distinguishable, each phase of the cell cycle has a distinct set of specialized biochemical processes that prepare the cell for initiation of cell division. G is a resting phase where the cell has left the cycle and has stopped dividing. The cell cycle starts with this phase. The word "
7478757
Cell growth


The term cell growth is used in the contexts of biological cell development and cell division (reproduction). When used in the context of cell development, the term refers to increase in cytoplasmic and organelle volume (G1 phase), as well as increase in genetic material (G2 phase) following the replication during S phase. This is not to be confused with growth in the context of cell division, referred to as proliferation, where a cell, known as the "mother cell", grows and divides to produce two
11095817
Cell cycle


prepare the cell for initiation of cell division. The eukaryotic cell cycle consists of four distinct phases: G phase, S phase (synthesis), G phase (collectively known as interphase) and M phase (mitosis and cytokinesis). M phase is itself composed of two tightly coupled processes: mitosis, in which the cell's nucleus divides, and cytokinesis, in which the cell's cytoplasm divides forming two daughter cells. Activation of each phase is dependent on the proper progression and completion of the previous one. Cells that
7478756
G1 phase


). G phase is particularly important in the cell cycle because it determines whether a cell commits to division or to leaving the cell cycle. If a cell is signaled to remain undivided, instead of moving onto the S phase, it will leave the G phase and move into a state of dormancy called the G phase. Most nonproliferating vertebrate cells will enter the G phase. Within the cell cycle, there is a stringent set of regulations known as the cell cycle control system that controls the timing and coordination of the phases
729027
Biochemical switches in the cell cycle


A series of biochemical switches control transitions between and within the various phases of the cell cycle. The cell cycle is a series of complex, ordered, sequential events that control how a single cell divides into two cells, and involves several different phases. The phases include the G1 and G2 phases, DNA replication or S phase, and the actual process of cell division, mitosis or M phase. During the M phase, the chromosomes separate and cytokinesis occurs. The switches maintain the orderly progression of the cell cycle and act
13326015
Cell division


it enters the M phase, where spindles are synthesized. The M phase, can be either mitosis or meiosis depending on the type of cell. Germ cells, or gametes, undergo meiosis, while somatic cells will undergo mitosis. After the cell proceeds successfully through the M phase, it may then undergo cell division through cytokinesis. The control of each checkpoint is controlled by cyclin and cyclin-dependent kinases. The progression of interphase is the result of the increased amount of cyclin. As the amount of cyclin increases, more
16324800
Cell biology


and development which involves cell growth, DNA replication, cell division, regeneration, and cell death. The cell cycle is divided into four distinct phases: G1, S, G2, and M. The G phase – which is the cell growth phase – makes up approximately 95% of the cycle. The proliferation of cells is instigated by progenitors; the cells then differentiate to become , where cells of the same type aggregate to form tissues, then organs and ultimately systems. The G phases along with the S phase – DNA
6481483
G1/S transition


, cell growth and division is unregulated causing tumor formation in the eye. To ensure proper cell division, the cell cycle utilizes numerous checkpoints to monitor cell progression and halt the cycle when processes go awry. These checkpoints include four DNA damage checkpoints, one unreplicated DNA checkpoint at the end of G2, one spindle assembly checkpoint in mitosis, and a chromosome segregation checkpoint during mitosis. Between G1 and S phase, three DNA damage checkpoints occur to ensure proper growth and synthesis of DNA prior to cell division. Damaged DNA during G1
20464053
Meiosis


two rounds of cell division to produce four daughter cells, each with half the number of chromosomes as the original parent cell. The two meiotic divisions are known as Meiosis I and Meiosis II. Before meiosis begins, during S phase of the cell cycle, the DNA of each chromosome is replicated so that it consists of two identical sister chromatids, which remain held together through sister chromatid cohesion. This S-phase can be referred to as "premeiotic S-phase" or "meiotic S-phase". Immediately following
19258405
Cell growth


accompanied by the formation of a new cell membrane. This is the physical division of "mother" and "daughter" cells. The M phase has been broken down into several distinct phases, sequentially known as prophase, prometaphase, metaphase, anaphase and telophase leading to cytokinesis. Cell division is more complex in eukaryotes than in other organisms. Prokaryotic cells such as bacterial cells reproduce by binary fission, a process that includes DNA replication, chromosome segregation, and cytokinesis. Eukaryotic cell division either involves mitosis or a more complex process
11095838
Cell growth


called phases. The first part, called G phase is marked by synthesis of various enzymes that are required for DNA replication. The second part of the cell cycle is the S phase, where DNA replication produces two identical sets of chromosomes. The third part is the G phase in which a significant protein synthesis occurs, mainly involving the production of microtubules that are required during the process of division, called mitosis. The fourth phase, M phase, consists of nuclear division (karyokinesis) and cytoplasmic division (cytokinesis),
11095837
Labile cell


. Acting as stem cells for these cell types. In labile cells, it is not a speed-up in the segments of the cell cycle (i.e. G1 phase, S phase, G2 phase and M phase), but rather a short or absent G0 phase that is responsible for the cells' constant division. Constantly dividing cells have a higher risk of becoming malignant and develop cancer, dividing uncontrollably. This is why muscle cancer is very rare, even though muscle tissue accounts for ~50% of total body weight,
15630182
Gene


membrane and is separated into the daughter cells as the membrane invaginates to split the cytoplasm into two membrane-bound portions. Binary fission is extremely fast compared to the rates of cell division in eukaryotes. Eukaryotic cell division is a more complex process known as the cell cycle; DNA replication occurs during a phase of this cycle known as S phase, whereas the process of segregating chromosomes and splitting the cytoplasm occurs during M phase. The duplication and transmission of genetic material from one generation of cells to the next is the basis for
1444226
S phase


S phase (Synthesis Phase) is the phase of the cell cycle in which DNA is replicated, occurring between G phase and G phase. Since accurate duplication of the genome is critical to successful cell division, the processes that occur during S-phase are tightly regulated and widely conserved. Entry into S-phase is controlled by the G1 restriction point (R), which commits cells to the remainder of the cell-cycle if there is adequate nutrients and growth signaling. This transition is essentially irreversible; after passing the
46805
Interphase


from interphase. In G1 phase decision for cell division is taking place... When G is completed, the cell enters a relatively brief period of nuclear and cellular division, composed of mitosis and cytokinesis, respectively. After the successful completion of mitosis and cytokinesis, both resulting daughter cells re-enter G of interphase. In the cell cycle, interphase is preceded by telophase and cytokinesis of the M phase. In alternative fashion, interphase is sometimes interrupted by G phase, which, in some circumstances, may then end and be
5267001
Cell cycle


the end of DNA replication and the splitting of the bacterial cell into two daughter cells. In cells with a nucleus, as in eukaryotes, the cell cycle is also divided into two main stages: interphase and the mitotic (M) phase (including mitosis and cytokinesis). During interphase, the cell grows, accumulating nutrients needed for mitosis, and undergoes DNA replication preparing it for cell division. During the mitotic phase, the replicated chromosomes and cytoplasm separate into two new daughter cells. To ensure the proper division of the
7478754
G1 phase


G phase and the S phase in which the cell is cleared for progression into the S phase. Reasons the cell would not move into the S phase include insufficient cell growth, damaged DNA, or other preparations have not been completed. At the G/S checkpoint, formation of the G/S cyclin with Cdk to form a complex commits the cell to a new division cycle. These complexes then activate S-Cdk complexes that move forward with DNA replication in the S phase. Concurrently, anaphase-promoting complex (
729033
Interphase


, in which the cell obtains nutrients and metabolizes them, grows, reads its DNA, and conducts other "normal" cell functions. The majority of eukaryotic cells spend most of their time in interphase. This phase was formerly called the resting phase. However, interphase does not describe a cell that is merely resting; rather, the cell is living and preparing for later cell division, so the name was changed. A common misconception is that interphase is the first stage of mitosis. However, since mitosis is the division
5266998
Actomyosin ring


The cell cycle is divided into two primary phases: DNA synthesis or "S phase" and Mitosis or "M phase". During the "S phase", duplication of chromosomes occurs whereas "M phase" is characterized by two processes known as nuclear (mitosis) and cytoplasmic (cytokinesis) divisions. The Actomyosin ring is a prominent structure during cytoplasmic division or cytokinesis (i.e., splitting from the parent cell after duplication and segregation of the genetic material has been completed). The ring forms perpendicular to the axis of
3442065
Platypus


and relies on the yolk sac for sustenance. The yolk is absorbed by the developing young. During the second phase, the digits develop, and in the last phase, the egg tooth appears. Most mammal zygotes go through holoblastic cleavage, meaning that following fertilisation the ovum is split due to cell divisions into multiple, divisible daughter cells. This is in comparison to the more ancestral process of meroblastic division in non-mammals (including platypuses), which causes the ovum to split but not completely. This causes the cells
4252819
Interphase


Interphase is the phase of the cell cycle in which a typical cell spends most of its life. If, we consider that the total event (interphase and mitotic cell division) take place about 24 hrs. then the interphase is of 23 hrs. Interphase can also be thought of as lasting for 90% of the cell's life, while Mitosis usually lasts for 10%. During this phase, the cell copies its DNA in preparation for mitosis. Interphase is the 'daily living' or metabolic phase of the cell
5266997
Cell cycle checkpoint


main indication for a cell to "restrict" and not enter the cell cycle. The decision to commit to a new round of cell division occurs when the cell activates cyclin-CDK-dependent transcription which promotes entry into S phase. This check point ensures the further process. During early G1, there are three transcriptional repressors, known as pocket proteins, that bind to E2F transcription factors. The E2F gene family is a group of transcription factors that target many genes that are important for control of the cell cycle, including
17927923
Blastula


fertilization and is therefore exclusively from the mother. In many organisms including "Xenopus" and "Drosophila", the mid-blastula transition usually occurs after a particular number of cell divisions for a given species, and is defined by the ending of the synchronous cell division cycles of the early blastula development, and the lengthening of the cell cycles by the addition of the G1 and G2 phases. Prior to this transition, cleavage occurs with only the synthesis and mitosis phases of the cell cycle. The addition of the two growth
5177304
Neurogenins


exocrine cells have been reprogrammed into cells with an islet cell-like phenotype following direct expression of NGN3 or manipulation that leads to its expression. The development of the pancreas is broken up into three phases, primary phase, secondary phase, and tertiary phase. Ngn3 is active in the primary and secondary phase. In the primary phase Ngn3 assists in α cell differentiation and in the secondary phase another wave of Ngn3 assists in differentiation of β cells, pancreatic polypeptide cells, and δ cells. Differentiation is marked as complete after the
3067473
Fis


structure and the initiation of DNA replication. It is a nucleoid-associated protein in Escherichia coli that is abundant during early exponential growth in rich medium but is in short supply during stationary phase. When stationary-phase cells are subcultured into a rich medium, Fis levels increase from less than 100 to over 50,000 copies per cell prior to the first cell division. As cells enter exponential growth, nascent synthesis is largely shut off, and intracellular Fis levels decrease as a function of cell division. Fis synthesis also transiently increases when
12239757
Cell cycle


p53. If the DNA is damaged, p53 will either repair the DNA or trigger the apoptosis of the cell. If p53 is dysfunctional or mutated, cells with damaged DNA may continue through the cell cycle, leading to the development of cancer. The relatively brief "M phase" consists of nuclear division (karyokinesis). It is a relatively short period of the cell cycle. M phase is complex and highly regulated. The sequence of events is divided into phases, corresponding to the completion of one set of activities and
7478764
Interphase


of the nucleus, prophase is actually the first stage. In interphase, the cell gets itself ready for mitosis or meiosis. Somatic cells, or normal diploid cells of the body, go through mitosis in order to reproduce themselves through cell division, whereas diploid germ cells (i.e., primary spermatocytes and primary oocytes) go through meiosis in order to create haploid gametes (i.e., sperm and ova) for the purpose of sexual reproduction. Chromosomes are copied. There are three stages of cellular interphase, with each phase ending when
5266999
Trichonympha


as well as a new parabasal body. Sexual reproduction in "Trichonympha" occurs in three distinct phases: gametogenesis, fertilization and meiosis. Gametogenesis occurs when gametes are produced by the division of a haploid cell that has encysted in response to the wood roach host molting. The nucleus and the cytoplasm of the haploid cell divide to produce two unequal gametes. The unequal division is caused by the production of unequal daughter chromosomes, each of which goes to a specific pole. One of the gametes, referred to by Cleveland as the
5036769
G1 phase


checkpoint because it does not determine whether cell conditions are ideal to move on to the next phase, but it changes the course of the cell. After a vertebrate cell has been in the G phase for about three hours, the cell enters a restriction point in which it is decided whether the cell will move forward with the G phase or move into the dormant G phase. This point also separates two halves of the G phase; the post-mitotic and pre-mitotic phases. Between the beginning of the G phase
729030
Thymidine kinase in clinical chemistry


tissue, and so initially they were termed fetal and adult thymidine kinases. Soon it was shown that TK1 is present in the cytoplasm only in anticipation of cell division (cell cycle-dependent) whereas the presence of TK2, which is located in the mitochondria, is cell cycle-independent. TK1 is synthesized by the cell during the S phase of cell division. After cell division is completed, TK1 is degraded intracellularly, so that it does not pass into body fluids after normal cell division. The TK enzyme suggested as
3096615
G2 phase


resides in G phase. During mitotic S phase, DNA replication produces two nearly identical sister chromatids. DNA double-strand breaks that arise after replication has progressed or during the G2 phase can be repaired before cell division occurs (M-phase of the cell cycle). Thus, during the G2 phase, double-strand breaks in one sister chromatid may be repaired by homologous recombinational repair using the other intact sister chromatid as template. In vertebrate cells, the G/M DNA damage checkpoint consists of an arrest of the
18915467
Embryonic stem cell


. Thus, mouse ES cells predominantly use high fidelity homologous recombinational repair (HRR) to repair DSBs. This type of repair depends on the interaction of the two sister chromosomes formed during S phase and present together during the G2 phase of the cell cycle. HRR can accurately repair DSBs in one sister chromosome by using intact information from the other sister chromosome. Cells in the G1 phase of the cell cycle (i.e. after metaphase/cell division but prior the next round of replication) have only one copy of each chromosome (
18380640
Myxogastria


in this phase, they cross-fertilise to a diploid zygote through the fusion of protoplasms and nuclei. The conditions which trigger this are not known. The diploid zygote becomes a multinucleated plasmodium through multiple nuclear divisions without further cell division. If the resulting cells were peritrichous, they change their shape before the fusion from the peritrichous form to the myxamoeba. For the production of a zygote, cells of different mating types (heterothallic) are required. The second trophic phase begins with the development of the plasmodium. The multinucleated organism
4900298
G0 phase


reversible G phases can be found in non-stem cells such as mature hepatocytes. Hepatocytes are typically quiescent in normal livers but undergo limited replication (less than 2 cell divisions) during liver regeneration after partial hepatectomy. However, in certain cases, hepatocytes can experience immense proliferation (more than 70 cell divisions) indicating that their proliferation capacity is not hampered by existing in a reversible quiescent state. Often associated with aging and age-related diseases in vivo, senescent cells can be found in many renewable tissues, including the stroma
22036738
Autospore


cell wall and remain attached to the mother cell. An autospore is defined one of the daughter cells formed by the internal division of a single cell. Autospores are formed as a result of fission in the mitotic phase of cell division of green algae. There are multiple methods that a cell can take to form autospores. The cell can undergo a multiple fission after 2 nuclear divisions where 4 autospores will form which is the preferred mechanism in organisms such as "P. subcapitata". In addition to this mechanism, there is binary
11848227
Cancer immunology


Cancer immunoediting is a process in which immune system interacts with tumor cells. It consists of three phases: elimination, equilibrium and escape. These phases are often referred to as "the three Es" of cancer immunoediting. Both, adaptive and innate immune system participate in immunoediting. In the elimination phase, the immune response leads to destruction of tumor cells and therefore to tumor suppression. However, some tumor cells may gain more mutations, change their characteristics and evade the immune system. These cells might enter the equilibrium phase,
2803114
Cell growth


in which cell division occurs after a constant volume has been added since the previous division. By always growing by the same amount, cells born smaller or larger than average naturally converge to an average size equivalent to the amount added during each generation. Cell reproduction is asexual. For most of the constituents of the cell, growth is a steady, continuous process, interrupted only briefly at M phase when the nucleus and then the cell divide in two. The process of cell division, called cell cycle, has four major parts
11095836
Cell cycle


the growth phase. During this phase, the biosynthetic activities of the cell, which are considerably slowed down during M phase, resume at a high rate. The duration of G is highly variable, even among different cells of the same species. In this phase, the cell increases its supply of proteins, increases the number of organelles (such as mitochondria, ribosomes), and grows in size. In G phase, a cell has three options. The deciding point is called check point (Restriction point). This
7478761
Thymidine kinase


be activated and converted to a tetramer in this way, showing that the enzyme occurring in cells has been modified after synthesis. TK1 is synthesized by the cell during the S phase of cell division. After cell division is completed, TK1 is degraded intracellularly and does not pass to body fluids after normal cell division. There is a feed-back regulation of the action of thymidine kinase in the cell: thymidine triphosphate (TTP), the product of the further phosphorylation of thymidine, acts as an inhibitor to thymidine kinase.
12247522
Genome instability


S/G2 phase in the presence of DNA damage caused by radiation. The yeast cells with defective rad9 failed to arrest following radiation, continued cell division and died rapidly while the cells with wild-type rad9 successfully arrested in late S/G2 phase and remained viable. The cells that arrested were able to survive due to the increased time in S/G2 phase allowing for DNA repair enzymes to function fully. There are hotspots in the genome where DNA sequences are prone to gaps and breaks after inhibition of DNA synthesis such
6731997
Spindle checkpoint


Only this pattern of attachment will ensure that each daughter cell receives one copy of the chromosome. When cells are ready to divide, because cell size is big enough or because they receive the appropriate stimulus, they activate the mechanism to enter into the cell cycle, and they duplicate most organelles during S (synthesis) phase, including their centrosome. Therefore, when the cell division process will end, each daughter cell will receive a complete set of organelles. At the same time, during S phase all cells must duplicate their
13558838
Cell biology


replication, damage and repair – are considered to be the inter-phase portion of the cycle, while the M phase (mitosis and ) is the cell division portion of the cycle. The cell cycle is regulated by a series of signalling factors and complexes such as cyclin-dependent kinase and p53, to name a few. When the cell has completed its growth process, and if it is found to be damaged or altered, it undergoes cell death, either by apoptosis or necrosis, in order to eliminate the threat
6481484
Tracy Sonneborn


ordinated? Sonneborn surgically removed a small section of cell wall and replaced it rotated by 180 degrees. The cortex with the cilia in the replaced section continued to 'wave' in the same direction as they had before surgery, i.e. now in antiphase to the others. What was remarkable is that both daughters of paramecium on which this operation had been performed also showed the same trait of a reverse phase wave if the reversal overlapped the division plane. If the reversed cortex did not overlap the division plane then only one the progeny
5073178
G0 phase


, H3K4me3 and H3K27me3, are two major histone methylation patterns that form a bivalent domain and are located near transcription initiation sites. These epigenetic markers have been found to regulate lineage decisions in embryonic stem cells as well as control quiescence in hair follicle and muscle stem cells via chromatin modification. Functional tumor suppressor genes, particularly p53 and Rb gene, are required to maintain stem cell quiescence and prevent exhaustion of the progenitor cell pool through excessive divisions. For example, deletion of all three components of the Rb family of proteins has been
22036731
Cyclin-dependent kinase 10


Cell division protein kinase 10 is an enzyme that in humans is encoded by the "CDK10" gene. The protein encoded by this gene belongs to the CDK subfamily of the Ser/Thr protein kinase family. The CDK subfamily members are highly similar to the gene products of S. cerevisiae cdc28, and S. pombe cdc2, and are known to be essential for cell cycle progression. This kinase has been shown to play a role in cellular proliferation. Its function is limited to cell cycle G2-M phase. At least three alternatively spliced
1947790
Nuclear DNA


that during meiosis, each of these phases occurs twice — once during the first round of division, called meiosis I, and again during the second round of division, called meiosis II. Prior to cell division, the DNA material in the original cell must be duplicated so that after cell division, each new cell contains the full amount of DNA material. The process of DNA duplication is usually called replication. The replication is termed semiconservative since each new cell contains one strand of original DNA and one newly synthesized strand of DNA
20102968
Midblastula


cell cycle begins to slow down and the G1 and G2 phases are added to the cell cycle. The addition of these phases allows the cell to have more time to proofread the new genetic material it is making to ensure there are no mutations. The asynchronous nature of the cell divisions is an important change that occurs during/after the MBT. The timing of MBT varies between different organisms. Zebrafish MBT occurs at cycle 10, but it occurs at cycle 13 in both "Xenopus" and "Drosophila". Cells are
9942598
Cell cycle


cell, there are control mechanisms known as cell cycle checkpoints. The cell-division cycle is a vital process by which a single-celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed. After cell division, each of the daughter cells begin the interphase of a new cycle. Although the various stages of interphase are not usually morphologically distinguishable, each phase of the cell cycle has a distinct set of specialized biochemical processes that
7478755
Ueli Schibler


of self-sustained, autonomous oscillators in the peripheral tissue, Schibler and his colleagues found evidence for interaction between the circadian clock and the timing of cell division. Single-cell recordings revealed how circadian gene expression in fibroblasts persists during cell division, and how cell division can phase shift the circadian cycle of the dividing cells. Due to the central role of Period (PER) and Cryptochrome (CRY) proteins in the negative feedback loop of the circadian clock, Schibler and colleagues posited the PER-CRY complex concentration to be
13856727
Cell cycle


check point is called the restriction point or START and is regulated by G/S cyclins, which cause transition from G to S phase. Passage through the G check point commits the cell to division. The ensuing S phase starts when DNA synthesis commences; when it is complete, all of the chromosomes have been replicated, i.e., each chromosome consists of two sister chromatids. Thus, during this phase, the amount of DNA in the cell has doubled, though the ploidy and number of chromosomes are unchanged. Rates of
7478762
Chloroplast


found in a mature photosynthetic plant cell. If the cell divides, chloroplast division provides the additional chloroplasts to partition between the two daughter cells. In single-celled algae, chloroplast division is the only way new chloroplasts are formed. There is no proplastid differentiation—when an algal cell divides, its chloroplast divides along with it, and each daughter cell receives a mature chloroplast. Almost all chloroplasts in a cell divide, rather than a small group of rapidly dividing chloroplasts. Chloroplasts have no definite S-phase—their DNA
6481869
Mitochondrion


single-celled eukaryotes, their growth and division is linked to the cell cycle. For example, a single mitochondrion may divide synchronously with the nucleus. This division and segregation process must be tightly controlled so that each daughter cell receives at least one mitochondrion. In other eukaryotes (in mammals for example), mitochondria may replicate their DNA and divide mainly in response to the energy needs of the cell, rather than in phase with the cell cycle. When the energy needs of a cell are high, mitochondria grow and divide
19833239
CDC6


Cell division control protein 6 homolog is a protein that in humans is encoded by the "CDC6" gene. The protein encoded by this gene is highly similar to Saccharomyces cerevisiae Cdc6, a protein essential for the initiation of DNA replication. This protein functions as a regulator at the early steps of DNA replication. It localizes in the cell nucleus during cell cycle phase G1, but translocates to the cytoplasm at the start of S phase. The subcellular translocation of this protein during the cell cycle is regulated through its phosphorylation by cyclin
6673199
Centrosome


making cilia and flagella. The centrosome is copied only once per cell cycle so that each daughter cell inherits one centrosome, containing two structures called centrioles (see also: centrosome cycle). The centrosome replicates during the S phase of the cell cycle. During the prophase in the process of cell division called mitosis, the centrosomes migrate to opposite poles of the cell. The mitotic spindle then forms between the two centrosomes. Upon division, each daughter cell receives one centrosome. Aberrant numbers of centrosomes in a cell have been associated
11134266
Cell (biology)


occurs during the S phase of the cell cycle. In meiosis, the DNA is replicated only once, while the cell divides twice. DNA replication only occurs before meiosis I. DNA replication does not occur when the cells divide the second time, in meiosis II. Replication, like all cellular activities, requires specialized proteins for carrying out the job. Between successive cell divisions, cells grow through the functioning of cellular metabolism. Cell metabolism is the process by which individual cells process nutrient molecules. Metabolism has two distinct divisions: catabolism
3756013
Phase-contrast microscopy


to study living cells and how they proliferate through cell division. It is one of the few methods available to quantify cellular structure and components that does not use fluorescence. After its invention in the early 1930s, phase-contrast microscopy proved to be such an advancement in microscopy that its inventor Frits Zernike was awarded the Nobel Prize in Physics in 1953. The basic principle to making phase changes visible in phase-contrast microscopy is to separate the illuminating (background) light from the specimen-scattered light (which makes up the
19708714
Triple phase boundary


A "triple phase boundary" (TPB) is a geometrical class of phase boundary and the location of contact between three different phases. A simple example of a TPB is a coastline where land, air and sea meet to create an energetic location driven by solar, wind and wave energy capable of supporting a high level of biodiversity. This concept is particularly important in the description of electrodes in fuel cells and batteries. For example for fuel cells, the three phases are an ion conductor (electrolyte), an electron conductor
5052547
Temperature measurement


the existence of triple point cells. Triple points are conditions of pressure, volume and temperature such that three phases are simultaneously present, for example solid, vapor and liquid. For a single component there are no degrees of freedom at a triple point and any change in the three variables results in one or more of the phases vanishing from the cell. Therefore, triple point cells can be used as universal references for temperature and pressure (see Gibbs phase rule). Under some conditions it becomes possible to measure temperature by a
7618851
Plant embryogenesis


can occur. Then during the "initiation of cell divisions", multicellular structures begin to form, which are contained by the exine wall. The last step of androgenesis is "pattern formation", where the embryo-like structures are released out of the exile wall, in order for pattern formation to continue. After these three phases occur, the rest of the process falls in line with the standard embryogenesis events. Embryonic tissue is made up of actively growing cells and the term is normally used to describe the early formation
4866837
G0 phase


restricted. Three G states exist and can be categorized as either reversible (quiescent) or irreversible (senescent and differentiated). Each of these three states can be entered from the G phase before the cell commits to the next round of the cell cycle. Quiescence refers to a reversible G state where subpopulations of cells reside in a 'quiescent' state before entering the cell cycle after activation in response to extrinsic signals. Quiescent cells are often identified by low RNA content, lack of cell proliferation markers, and increased label retention
22036727
Embryonic stem cell


are always expressed at high levels. Cyclin-dependent kinases such as CDK2 that promote cell cycle progression are overactive, in part due to downregulation of their inhibitors. Retinoblastoma proteins that inhibit the transcription factor E2F until the cell is ready to enter S phase are hyperphosphorylated and inactivated in ESCs, leading to continual expression of proliferation genes. These changes result in accelerated cycles of cell division. Although the shortened G1 phase has been linked to maintenance of pluripotency, ESCs grown in serum-free 2i conditions do express hypo-phosphorylated active
18380630
Cohesin


enter into the G1 stage of cell cycle, and they duplicate most organelles during S (synthesis) phase, including their centrosome. Therefore, when the cell division process will end, each daughter cell will receive a complete set of organelles. At the same time, during S phase all cells must duplicate their DNA very precisely, a process termed DNA replication. Once DNA replication has finished, in eukaryotes the DNA molecule is compacted and condensed, to form the mitotic chromosomes, each one constituted by two sister chromatids, which
5730695
Mitotic inhibitor


move and separate chromosomes and other components of the cell for cell division (mitosis). Mitotic inhibitors interfere with the assembly and disassembly of tubulin into microtubule polymers. This interrupts cell division, usually during the mitosis (M) phase of the cell cycle when two sets of fully formed chromosomes are supposed to separate into daughter cells. Examples of mitotic inhibitors frequently used in the treatment of cancer include paclitaxel, docetaxel, vinblastine, vincristine, and vinorelbine. Colchicine and griseofulvin are mitotic inhibitors used in the treatment of gout and toenail
843026
S phase


, the cell continuously scrutinizes its genome for abnormalities. Detection of DNA damage induces activation of three canonical S-phase "checkpoint pathways" that delay or arrest further cell cycle progression: In addition to these canonical checkpoints, recent evidence suggests that abnormalities in histone supply and nucleosome assembly can also alter S-phase progression. Depletion of free histones in "Drosophila" cells dramatically prolongs S-phase and causes permanent arrest in G2-phase. This unique arrest phenotype is not associated with activation of canonical DNA damage pathways, indicating that nucleosome
46816
Cyclin B


Cyclin B plays in integral role in many types of cancer. Hyperplasia (uncontrolled cell growth) is one of the hallmarks of cancer. Because cyclin B is necessary for cells to enter mitosis and therefore necessary for cell division, cyclin B levels are often de-regulated in tumors. When cyclin B levels are elevated, cells can enter M phase prematurely and strict control over cell division is lost, which is a favorable condition for cancer development. On the other hand, if cyclin B levels are depleted the cyclin B/
21542586
Symbiodinium


to as mitotic or vegetative growth), cells undergo a diel cycle of karyokinesis (chromosome/nuclear division) in darkness. The mother cell then divides (cytokinesis) soon after exposure to light and releases two motile cells. The initiation and duration of motility varies among species. Approaching or at the end of the photoperiod the mastigotes cease swimming, release their flagella, and undergo a rapid metamorphosis into the coccoid form. As cultures reach stationary growth phase, fewer and fewer motile cells are observed, indicating slower division rates.
298730
Triple phase boundary


, and a virtual "porosity" phase for transporting gaseous or liquid fuel molecules. The electrochemical reactions that fuel cells use to produce electricity occur in the presence of these three phases. Triple phase boundaries are thus the electrochemically active sites within electrodes. The oxygen reduction reaction that occurs at a solid oxide fuel cell's (SOFC) cathode, can be written as follows: Different mechanisms bring these reactants to a TPB to carry out this reaction. The kinetics of this reaction is one of the limiting factors in cell performance,
5052548
Porcine circovirus


E3 ubiquitin ligase normally interacts with p53 during the cell division cycle and prevents it from halting the cell division cycle at S-phase. However, ORF3 also interacts with pPirh2 at the same region as p53 and causes an upregulation of p53 expression. This increase in p53 stops the cell division cycle and the result of this is p53 mediated apoptosis, which releases PCV into the extracellular environment. On 22 March 2010, the U.S. Food and Drug Administration (FDA) recommended suspending the use Rotarix, one of two vaccines licensed in
17390496
History of biology


of life, though they opposed the idea that (3) all cells come from the division of other cells. Thanks to the work of Robert Remak and Rudolf Virchow, however, by the 1860s most biologists accepted all three tenets of what came to be known as cell theory. Cell theory led biologists to re-envision individual organisms as interdependent assemblages of individual cells. Scientists in the rising field of cytology, armed with increasingly powerful microscopes and new staining methods, soon found that even single cells were far more complex than
15242035
Saccharomyces cerevisiae


and sizes. Similarly, stem cells use asymmetric division for self-renewal and differentiation. For many cells, M phase does not happen until S phase is complete. However, for entry into mitosis in "S. cerevisiae" this is not true. Cytokinesis begins with the budding process in late G1 and is not completed until about halfway through the next cycle. The assembly of the spindle can happen before S phase has finished duplicating the chromosomes. Additionally, there is a lack of clearly defined G2 in between M and S.
9431274
Cyclin B


CDK1 complex cannot form, cells cannot enter M phase and cell division slows down. Some anti-cancer therapies have been designed to prevent cyclin B/CDK1 complex formation in cancer cells to slow or prevent cell division. Most of these methods have targeted the CDK1 subunit, but there is an emerging interest in the oncology field to target cyclin B as well. Cyclin levels can easily be determined through immunohistological analysis of tumor biopsies. The fact that cyclin B is often disregulated in cancer cells makes cyclin B an attractive
21542587
Cell cycle


, p53 etc. mutate, they may cause the cell to multiply uncontrollably, forming a tumor. Although the duration of cell cycle in tumor cells is equal to or longer than that of normal cell cycle, the proportion of cells that are in active cell division (versus quiescent cells in G phase) in tumors is much higher than that in normal tissue. Thus there is a net increase in cell number as the number of cells that die by apoptosis or senescence remains the same. The cells which are actively undergoing cell
7478794
Hayflick limit


female cells (which it could not) then the cessation of normal cell replication was governed by an internal counting mechanism. These results disproved Carrel's immortality claims and established the Hayflick limit as a credible biological theory. Unlike Carrel's experiment, Hayflick's have been successfully repeated by other scientists. Hayflick describes three phases in the life of normal cultured cells. At the start of his experiment he named the primary culture "phase one". Phase two is defined as the period when cells are proliferating; Hayflick called this the
105592
Cardiac action potential


three Na into the cell. During this phase the membrane is most permeable to K, which can travel into or out of cell through leak channels, including the inwardly rectifying potassium channel. Therefore, the resting membrane potential is mainly determined by K equilibrium potential and can be calculated using the Goldman-Hodgkin-Katz voltage equation. However, pacemaker cells are never at rest. In these cells, phase 4 is also known as the pacemaker potential. During this phase, the membrane potential slowly becomes more positive, until it
13425177
Ridge (biology)


locate a gene and measure its distance to other genes. The first eukaryote genome ever sequenced was that of Saccharomyces cerevisiae, or budding yeast, in 1996. Half a year after that Velculescu et al. (1997) published a research in which they had integrated SAGE data with the now available genome map. During a cell cycle different genes are active in a cell. Therefore, they used SAGE data from three moments of the cell cycle (log phase, S phase-arrested and G2/M-phase arrested cells
373889
Ornithocercus


been found to show phased cell division (specific dividing times for species throughout the day). By analyzing the states of the megacytic zones and bridges between daughter cells, a study off the coast of Brazil in the South Atlantic Ocean found that while cell division in "O. steinii" required high light intensity, "O. magnificus" and "O. thumii" utilized the days first light. Sexual reproduction and cyst formation are not known in "Ornithocercus." In the early 20th century, radiation schemes based on morphologies in cell
13408046
Paclitaxel


adverse reactions to paclitaxel. Paclitaxel is one of several cytoskeletal drugs that target tubulin. Paclitaxel-treated cells have defects in mitotic spindle assembly, chromosome segregation, and cell division. Unlike other tubulin-targeting drugs, such as colchicine, that inhibit microtubule assembly, paclitaxel stabilizes the microtubule polymer and protects it from disassembly. Chromosomes are thus unable to achieve a metaphase spindle configuration. This blocks the progression of mitosis and prolonged activation of the mitotic checkpoint triggers apoptosis or reversion to the G0-phase of the cell cycle without cell division.
16206854
Eukaryotic DNA replication


cell division cycle 45 (Cdc45) protein is also essential for initiating DNA replication. Studies have shown that Mcm is critical for the loading of Cdc45 onto chromatin and this complex containing both Mcm and Cdc45 is formed at the onset of the S phase of the cell cycle. Cdc45 targets the Mcm protein complex, which has been loaded onto the chromatin, as a component of the pre-RC at the origin of replication during the G stage of the cell cycle. Cell division cycle 45 (Cdc45) protein is a critical
8976391
Follicular phase


secretion of follicular thecal cells and increases LH receptor expression on granulosa cells. Throughout the entire follicular phase, rising estrogen levels in the blood stimulates growth of the endometrium and myometrium of the uterus. It also causes endometrial cells to produce receptors for progesterone, which helps prime the endometrium to respond to rising levels of progesterone during the late proliferative phase and throughout the luteal phase. Two or three days before LH levels begin to increase, usually by day seven of the cycle, one (or occasionally two) of the recruited follicles
7243548
Baculoviridae


spread the infection systemically. During budding, BV acquires a loosely fitting host cell membrane with expressed and displayed viral glycoproteins. Baculovirus infection can be divided to three distinct phases: While BV is produced in the late phase, the ODV form is produced in the very late phase acquiring the envelope from host cell nucleus and embedded in the matrix of occlusion body protein. These occlusion bodies are released when cells lyse to further spread baculovirus infection to next host. The extensive lysis of cells frequently causes the host insect to literally disintegrate,
5644424
Clandestine cell system


certain types of insurgency grow in power, they deemphasize the cell system. They may still use cells for leadership security, but if overt violence by organized units becomes significant, cells become less important. In Mao's three-stage doctrine, cells are still useful in Phase II to give cover to part-time guerillas, but as the insurgency creates full-time military units in Phase III, the main units become the focus, not the cells. Different varieties of insurgency place their cells differently with respect to the existing
15814208
Cell cycle


regulate the progress of the cell cycle. Checkpoints prevent cell cycle progression at specific points, allowing verification of necessary phase processes and repair of DNA damage. The cell cannot proceed to the next phase until checkpoint requirements have been met. Checkpoints typically consist of a network of regulatory proteins that monitor and dictate the progression of the cell through the different stages of the cell cycle. There are several checkpoints to ensure that damaged or incomplete DNA is not passed on to daughter cells. Three main checkpoints exist: the G/S
7478786
P16


. When organisms age, the expression of p16 increases to reduce the proliferation of stem cells. This reduction in the division and production of stem cells protects against cancer while increasing the risks associated with cellular senescence. p16 is an inhibitor of cyclin-dependent kinases (CDK). It slows down the cell cycle by prohibiting progression from G1 phase to S phase. Otherwise, CDK4/6 binds cyclin D and forms an active protein complex that phosphorylates retinoblastoma protein (pRB). Once phosphorylated, pRB dissociates from the transcription factor E2F1.
11026985
High-temperature superconductivity


which consists of two sheared crystallographic unit cells. The unit cell of these phases has double Bi–O planes which are stacked in a way that the Bi atom of one plane sits below the oxygen atom of the next consecutive plane. The Ca atom forms a layer within the interior of the CuO layers in both Bi-2212 and Bi-2223; there is no Ca layer in the Bi-2201 phase. The three phases differ with each other in the number of CuO planes; Bi-2201, Bi-2212 and Bi-2223 phases have one, two and three
13442016
Ascomycota


extrude the cell wall. New cell wall material is incorporated during this phase. Cell contents are forced into the progeny cell, and as the final phase of mitosis ends a cell plate, the point at which a new cell wall will grow inwards from, forms. There are three subphyla that are described and accepted: Several outdated taxon names—based on morphological features—are still occasionally used for species of the Ascomycota. These include the following sexual (teleomorphic) groups, defined by the structures of their sexual fruiting bodies
4484739
Retinoblastoma protein


15 possible phosphorylation sites. Generally, phosphorylation causes interdomain locking, which changes Rb’s conformation and prevents binding to target proteins. Different sites may be phosphorylated at different times, giving rise to many possible conformations and likely many functions/ activity levels. Rb restricts the cell's ability to replicate DNA by preventing its progression from the G1 (first gap phase) to S (synthesis phase) phase of the cell division cycle. Rb binds and inhibits E2 promoter-binding–protein-dimerization partner (E2F-DP) dimers,
8749129
DNA replication


in S phase of cell division and their number per nucleus is far smaller than the number of genomic replication forks. P. Heun et al.(2001) tracked GFP-tagged replication foci in budding yeast cells and revealed that replication origins move constantly in G1 and S phase and the dynamics decreased significantly in S phase. Traditionally, replication sites were fixed on spatial structure of chromosomes by nuclear matrix or lamins. The Heun’s results denied the traditional concepts, budding yeasts don't have lamins, and support that replication origins self-assemble and
9095951
Mitosis


the centrosomes) and the nucleolus reappears. Both sets of chromosomes, now surrounded by new nuclear membrane, begin to "relax" or decondense. Mitosis is complete. Each daughter nucleus has an identical set of chromosomes. Cell division may or may not occur at this time depending on the organism. Cytokinesis is not a phase of mitosis but rather a separate process, necessary for completing cell division. In animal cells, a cleavage furrow (pinch) containing a contractile ring develops where the metaphase plate used to be, pinching
104220
Spindle poison


A spindle poison, also known as a spindle toxin, is a poison that disrupts cell division by affecting the protein threads that connect the centromere regions of chromosomes, known as spindles. Spindle poisons effectively cease the production of new cells by interrupting the mitosis phase of cell division at the spindle assembly checkpoint (SAC). However, as numerous and varied as they are, spindle poisons are not yet 100% effective at ending the formation of tumors (neoplasms). Although not 100% effective, substantive therapeutic efficacy has been
16853201
Cell cycle checkpoint


All living organisms are the products of repeated rounds of cell growth and division. During this process, known as the cell cycle, a cell duplicates its contents and then divides in two. The purpose of the cell cycle is to accurately duplicate each organism's DNA and then divide the cell and its contents evenly between the two resulting cells. In eukaryotes, the cell cycle consists of four main stages: G, during which a cell is metabolically active and continuously grows; S phase, during which DNA replication takes place;
17927918
Opalinidae


more trophonts. Nuclear divisions maintain the appropriate number of nuclei during this phase. As the host's breeding season approaches, the trophonts enter a phase known as palintomy -- a series of cell divisions with little or no overall growth or nuclear divisions. The resulting opalines, which become gradually smaller with fewer nuclei per individual, are called tomonts. At some point the small tomonts undergo encystment, and the cysts are released into the environment (i.e. the breeding pool of the anuran host) along with the feces. Sexual and asexual
5176769
Cell cycle checkpoint


G, during which cell growth continues and the cell synthesizes various proteins in preparation for division; and the M (mitosis) phase, during which the duplicated chromosomes (known as the sister chromatids) separate into two daughter nuclei, and the cell divides into two daughter cells, each with a full copy of DNA. Compared to the eukaryotic cell cycle, the prokaryotic cell cycle (known as binary fission) is relatively simple and quick: the chromosome replicates from the origin of replication, a new membrane is assembled, and
17927919