query: in which phase of cell cycle are chromosomes replicated

pos: Cell cycle it is complete, all of the chromosomes have been replicated, i.e., each chromosome has two (sister) chromatids. Thus, during this phase, the amount of DNA in the cell has effectively doubled, though the ploidy of the cell remains the same. Rates of RNA transcription and protein synthesis are very low during this phase. An exception to this is histone production, most of which occurs during the S phase. G2 phase occurs after DNA replication and is a period of protein synthesis and rapid cell growth to prepare the cell for mitosis. During this phase microtubules begin to reorganize to form

pos: Mitosis (synthesis), and G (second gap). During all three parts of interphase, the cell grows by producing proteins and cytoplasmic organelles. However, chromosomes are replicated only during the S phase. Thus, a cell grows (G), continues to grow as it duplicates its chromosomes (S), grows more and prepares for mitosis (G), and finally divides (M) before restarting the cycle. All these phases in the cell cycle are highly regulated by cyclins, cyclin-dependent kinases, and other cell cycle proteins. The phases follow one another in strict order and there are "checkpoints" that give the cell cues to proceed from one phase to

pos: G2 phase G2 phase G phase, or Gap 2 phase, is the second subphase of Interphase in the cell cycle directly preceding mitosis. It follows the successful completion of S phase, during which the cell’s DNA is replicated. G phase ends with the onset of prophase, the first phase of mitosis in which the cell’s chromatin condenses into chromosomes. G phase is a period of rapid cell growth and protein synthesis during which the cell prepares itself for mitosis. Curiously, G phase is not a necessary part of the cell cycle, as some cell types (particularly young "Xenopus" embryos and some cancers

pos: Meiosis 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 DNA replication, meiotic cells enter a prolonged G2-like stage known as meiotic prophase. During this time, homologous chromosomes pair with each other and undergo genetic recombination, a programmed process in which DNA is

pos: Cell cycle it is complete, all of the chromosomes have been replicated, i.e., each chromosome has two (sister) chromatids. Thus, during this phase, the amount of DNA in the cell has effectively doubled, though the ploidy of the cell remains the same. Rates of RNA transcription and protein synthesis are very low during this phase. An exception to this is histone production, most of which occurs during the S phase. G2 phase occurs after DNA replication and is a period of protein synthesis and rapid cell growth to prepare the cell for mitosis. During this phase microtubules begin to reorganize to form

pos: Establishment of sister chromatid cohesion Establishment of sister chromatid cohesion Sister chromatid cohesion refers to the process by which sister chromatids are paired and held together during certain phases of the cell cycle. Establishment of sister chromatid cohesion is the process by which chromatin-associated cohesin protein becomes competent to physically bind together the sister chromatids. In general, cohesion is established during S phase as DNA is replicated, and is lost when chromosomes segregate during mitosis and meiosis. Some studies have suggested that cohesion aids in aligning the kinetochores during mitosis by forcing the kinetochores to face opposite cell poles. Cohesin first associates with the chromosomes

pos: Cell division chromosomes must be replicated, and the duplicated genome must be separated cleanly between cells. A great deal of cellular infrastructure is involved in keeping genomic information consistent between generations. Interphase is the process a cell must go through before mitosis, meiosis, and cytokinesis. Interphase consists of three main stages: G1, S, and G2. G1 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 progressed or denied further development. In S phase, the chromosomes are replicated

pos: Neuronal cell cycle Kozminski, K.G. (2013). Cell cycle checkpoint regulators reach a zillion. Cell Cycle 12, 1501–1509. Neuronal cell cycle The Cell Cycle represents the life cycle of the biological cell, its creation, reproduction and eventual death. The process by which cells divide into two daughter cells is called mitosis. Once these cells are formed they enter G1, the phase in which many of the proteins needed to replicate DNA are made. After G1, the cells enter S phase during which the DNA is replicated. After S, the cell will enter G2 where the proteins required for mitosis to occur are synthesized. Unlike

pos: Neuronal cell cycle Neuronal cell cycle The Cell Cycle represents the life cycle of the biological cell, its creation, reproduction and eventual death. The process by which cells divide into two daughter cells is called mitosis. Once these cells are formed they enter G1, the phase in which many of the proteins needed to replicate DNA are made. After G1, the cells enter S phase during which the DNA is replicated. After S, the cell will enter G2 where the proteins required for mitosis to occur are synthesized. Unlike most cell types however, neurons are generally considered incapable of proliferating once they are

pos: S phase be scrutinized by a novel S-phase checkpoint. 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 restriction point, the cell will progress through S-phase

pos: S phase 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 restriction point, the cell will progress through S-phase even if environmental conditions become unfavorable. Accordingly,

pos: Cell growth 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 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,

pos: G1/S transition G1/S transition The G1/S transition is a stage in the cell cycle at the boundary between the G1 phase, in which the cell grows, and the S phase, during which DNA is replicated. It is a cell cycle check point where DNA integrity is assessed and the cell cycle can pause in response to improperly or partially replicated DNA. During this transition the cell makes decisions to become quiescent (enter G0), differentiate, make DNA repairs, or proliferate based on environmental cues and molecular signaling inputs. The G1/S transition occurs late in G1 and the absence or improper application of this

pos: Embryonic stem cell 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 (i.e. sister chromosomes aren’t present). Mouse ES cells lack a G1 checkpoint and do not undergo cell

pos: Centrosome cycle are of different ages, though. One centriole originates from the mother cell and the other is replicated from the mother centriole during the cell cycle. It is possible to distinguish between the two preexisting centrioles, because the mother and daughter centriole differ in both shape and function. For example, the mother centriole can nucleate and organize microtubules, whereas the daughter centriole can only nucleate. First, procentrioles begin to form near each preexisting centriole as the cell moves from the G1 phase to the S phase. During S and G2 phase of the cell cycle, the procentrioles elongate until they reach

pos: Ridge (biology) 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). Because in yeast all genes have a promoter unit of their own it was not suspected that genes would cluster near to each other but they did. Clusters were present on all 16 yeast chromosomes. A year later Cho et

pos: Biochemical switches in the cell cycle and SBF. 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 as checkpoints to

pos: Biochemical switches in the cell cycle 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 as checkpoints to ensure that

pos: Large tumor antigen after which the helicase continues unwinding. The major functions of LTag in the viral life cycle involve dysregulation of the host cell's cell cycle and replication of the virus's circular DNA genome. Because polyomavirus genome replication relies on the DNA replication machinery of the host cell, the cell must be in S phase (the part of the cell cycle in which the host cell's genome is normally replicated) in order to provide the necessary molecular machinery for viral DNA replication. The SV40 LTag can induce S phase and activate the host cell's DNA damage response. Coordinated actions of the OBD

pos: Mitosis to the chromosome. The lagging chromatid is excluded from both nuclei and is lost. Therefore, one of the daughter cells will be monosomic for that chromosome. "Endoreduplication" (or endoreplication) occurs when chromosomes duplicate but the cell does not subsequently divide. This results in polyploid cells or, if the chromosomes duplicates repeatedly, polytene chromosomes. Endoreduplication is found in many species and appears to be a normal part of development. Endomitosis is a variant of endoreduplication in which cells replicate their chromosomes during S phase and enter, but prematurely terminate, mitosis. Instead of being divided into two new daughter nuclei, the replicated

pos: Nondisjunction binding sites for spindle attachment. Cohesin is loaded onto newly replicated chromosomes in oogonia during fetal development. Mature oocytes have only limited capacity for reloading cohesin after completion of S phase. The prolonged arrest of human oocytes prior to completion of meiosis I may therefore result in considerable loss of cohesin over time. Loss of cohesin is assumed to contribute to incorrect microtubule-kinetochore attachment and chromosome segregation errors during meiotic divisions. The result of this error is a cell with an imbalance of chromosomes. Such a cell is said to be aneuploid. Loss of a single chromosome (2n-1), in which

pos: Small tumor antigen and LTag interact through their J domains with Hsc70 to increase its ATPase activity. Because polyomavirus genome replication relies on the DNA replication machinery of the host cell, the cell must be in S phase (the part of the cell cycle in which the host cell's genome is normally replicated) in order to provide the necessary molecular machinery for viral DNA replication. Viral proteins therefore promote dysregulation of the cell cycle and entry into S phase. This function is usually primarily provided by LTag through its interactions with retinoblastoma protein and p53. STag contributes to this process through its interaction

pos: Actomyosin ring 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 the spindle apparatus. and occurs towards the later stage of mitosis, the telophase, in which sister chromatids are

pos: Centrosome in 1888 by Theodor Boveri. Centrosomes are associated with the nuclear membrane during the prophase stage of the cell cycle. In mitosis the nuclear membrane breaks down and the centrosome nucleated microtubules can interact with the chromosomes to build the mitotic spindle. The mother centriole, the older of the two in the centriole pair, also has a central role in 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

pos: Polyomaviridae small tumor antigen (ST) and large tumor antigen (LT) - are expressed first, from a single alternatively spliced messenger RNA strand. These proteins serve to manipulate the host's cell cycle - dysregulating the transition from G1 phase to S phase, when the host cell's genome is replicated - because host cell DNA replication machinery is needed for viral genome replication. The precise mechanism of this dysregulation depends on the virus; for example, SV40 LT can directly bind host cell p53, but murine polyomavirus LT does not. LT induces DNA replication from the viral genome's non-coding control region (NCCR), after which

pos: Gene 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 molecular inheritance, and the link between the classical and molecular pictures of genes. Organisms inherit the characteristics of their parents because the cells of the offspring contain

pos: G2 phase not function strictly as activators of cyclin B1/CDK1 in G, as CDK2 has been shown to be required for activation of the p53-independent G checkpoint activity, perhaps through a stabilizing phosphorylation on Cdc6. CDK2-/- cells also have aberrantly high levels of Cdc25A. Cyclin A2/CDK1 has also been shown to mediate proteosomal destruction of Cdc25B. These pathways are often deregulated in cancer. G2 phase G phase, or Gap 2 phase, is the second subphase of Interphase in the cell cycle directly preceding mitosis. It follows the successful completion of S phase, during which the cell’s DNA is replicated. G phase ends

pos: Histone the synthesis of histone proteins: H1, H2A, H2B, H3, H4. These proteins are synthesized during S phase of the cell cycle. There are different mechanisms which contribute to the increase of histone synthesis. Yeast carry one or two copies of each histone gene, which are not clustered but rather scattered throughout chromosomes. Histone gene transcription is controlled by multiple gene regulatory proteins such as transcription factors which bind to histone promoter regions. In budding yeast, the candidate gene for activation of histone gene expression is SBF. SBF is a transcription factor that is activated in late G1 phase, when it

pos: Histone to be the removal of a segment of the 3’ end of the mRNA strand, and is dependent on association with stem-loop binding protein (SLBP). SLBP also stabilizes histone mRNAs during S phase by blocking degradation by the 3’hExo nuclease. SLBP levels are controlled by cell-cycle proteins, causing SLBP to accumulate as cells enter S phase and degrade as cells leave S phase. SLBP are marked for degradation by phosphorylation at two threonine residues by cyclin dependent kinases, possibly cyclin A/ cdk2, at the end of S phase. Metazoans also have multiple copies of histone genes clustered on chromosomes which

pos: Transposable element short direct repeats (a staggered cut in the target DNA filled by DNA polymerase) followed by inverted repeats (which are important for the TE excision by transposase). Cut-and-paste TEs may be duplicated if their transposition takes place during S phase of the cell cycle, when a donor site has already been replicated but a target site has not yet been replicated. Such duplications at the target site can result in gene duplication, which plays an important role in genomic evolution. Not all DNA transposons transpose through the cut-and-paste mechanism. In some cases, a replicative transposition is observed in which a

pos: Bruce William Stillman made up of six subunits that binds to cellular origins of DNA replication and coordinates the entire process of initiating a complete cycle of DNA replication throughout the entire cell genome. Soon after the discovery of ORC, Stillman’s group identified other initiation proteins that together form the pre-replication complex (pre-RC), which makes chromosomes competent for the subsequent initiation of DNA replication during the S phase of the cell cycle. His group’s recent studies have revealed the intricate details of the mechanism of the initiation of DNA replication and illuminated how this process is regulated throughout the cell cycle, including the

pos: Establishment of sister chromatid cohesion yeast, CARs tend to be rich in adenine-thymine base pairs. CARs are independent of origins of replication. Establishment of cohesion refers to the process by which chromatin-associated cohesin becomes cohesion-competent. Chromatin association of cohesin is not sufficient for cohesion. Cohesin must undergo subsequent modification ("establishment") to be capable of physically holding the sister chromosomes together. Though cohesin can associate with chromatin earlier in the cell cycle, cohesion is established during S phase. Early data suggesting that S phase is crucial to cohesion was based on the fact that after S phase, sister chromatids are always found in the bound state.

pos: Histone are localized in structures called Cajal bodies as determined by genome-wide chromosome conformation capture analysis (4C-Seq). Nuclear protein Ataxia-Telangiectasia (NPAT), also known as nuclear protein coactivator of histone transcription, is a transcription factor which activates histone gene transcription on chromosomes 1 and 6 of human cells. NPAT is also a substrate of cyclin E-Cdk2, which is required for the transition between G1 phase and S phase. NPAT activates histone gene expression only after it has been phosphorylated by the G1/S-Cdk cyclin E-Cdk2 in early S phase. This shows an important regulatory link between cell-cycle control and histone synthesis. Histone In

pos: Cell (biology) 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, in which the cell breaks down complex molecules to produce energy and reducing power, and

pos: Actomyosin ring from the center of the plane of division until it fuses with the existing cell wall. Cytokinesis:Actin-myosin ring assembly and contraction 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

pos: DNA unwinding element is replicated only once and that this is occurring in the proper location at the proper time. Operates in response to extracellular signals that coordinate initiation of division, differently from tissue to tissue. External signals trigger replication in S phase via production of cyclins which activate cyclin-dependent kinases (CDK) to form complexes. DNA replication in eukaryotes initiates upon origin recognition complex (ORC) binding to the origin. This occurs at G cell phase serving to drive the cell cycle forward into S phase. This binding allows for further factor binding to create a pre-replicative complex (pre-RC). Pre-RC triggered to initiate when

pos: Premature chromosome condensation prematurely. The appearance of a prematurely condensed chromosome depends on the stage that the interphase cell was in. Chromosomes that are condensed during the G phase are usually long and have a single strand, while chromosomes condensed during the S phase appear crushed. Condensation during the G phase yields long chromosomes with two chromatids. PCC was first reported in 1968, of viral-infected cells showing strange appearance of chromosomes. It was found that the strange appearance was selectively observed in S-phase nuclei, and therefore concluded that the nuclei of cells fused in mitotic cells condensed prematurely by unknown material which accumulated

pos: DNA replication factor CDT1 by minichromosome maintenance complexes (MCM2-7). The activity of CDT1 during the cell cycle is tightly regulated during the S phase by the protein geminin, which inhibits its, and by SCF, which ubiquinates the protein to tag it for proteasomal degradation. This regulation is important in preventing relicensing, thus ensuring that DNA is only replicated once per cell cycle. CDT1 belongs to a family of replication proteins conserved from yeast to humans. Examples of orthologs in other species include: DNA replication factor CDT1 has been shown to interact with SKP2. Cdt1 is recruited by the origin recognition complex in origin licensing.

pos: Cell cycle 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 prepare the cell for initiation of cell division The cell cycle consists of four distinct phases: G phase, S phase (synthesis), G phase (collectively known as interphase) and M phase (mitosis or meiosis). M phase is itself composed of two tightly

pos: Cyclin-dependent kinase 2 E2F transcription factors to express genes that promote entry into S phase where DNA is replicated prior to division. Additionally, NPAT, a known substrate of the Cdk2-Cyclin E complex, functions to activate histone gene transcription when phosphorylated. This increases the synthesis of histone proteins (the major protein component of chromatin), and subsequently supports the DNA replication stage of the cell cycle. Finally, at the end of S phase, the ubiquitin proteasome degrades cyclin E. Although Cdk2 is mostly dispensable in the cell cycle of normally functioning cells, it is critical to the abnormal growth processes of cancer cells. The CCNE1

pos: Origin recognition complex Cdc6, Tah11 (a.k.a. Cdt1), and the Mcm2-Mcm7 complex. Pre-RC assembly during G1 is required for replication licensing of chromosomes prior to DNA synthesis during S phase. Cell cycle-regulated phosphorylation of Orc2, Orc6, Cdc6, and MCM by the cyclin-dependent protein kinase Cdc28 regulates initiation of DNA replication, including blocking reinitiation in G2/M phase. The ORC is present throughout the cell cycle bound to replication origins, but is only active in late mitosis and early G1. In yeast, ORC also plays a role in the establishment of silencing at the mating-type loci Hidden MAT Left (HML) and Hidden MAT Right (HMR). ORC

pos: Spindle checkpoint 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 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,

pos: Ki-67 (protein) most of the protein is relocated to the surface of the chromosomes. Ki-67 protein is present during all active phases of the cell cycle (G, S, G, and mitosis), but is absent in resting (quiescent) cells (G). Cellular content of Ki-67 protein markedly increases during cell progression through S phase of the cell cycle. In breast cancer Ki67 identifies a high proliferative subset of patients with ER-positive breast cancer who derive greater benefit from adjuvant chemotherapy Ki-67 is an excellent marker to determine the growth fraction of a given cell population. The fraction of Ki-67-positive tumor cells (the "Ki-67 labeling

pos: Constitutive heterochromatin mechanism to overcome the silencing that occurs in the rest of the heterochromatin. There are many proposed models for how the genes in these regions are expressed, including the insulation, denial, integration, exploitation, and TE restraining models. When genes are placed near a region of constitutive heterochromatin, their transcription is usually silenced. This is known as position-effect variegation and can lead to a mosaic phenotype. Constitutive heterochromatin is replicated late in S phase of the cell cycle and does not participate in meiotic recombination. Histone modifications are one of the main ways that the cell condenses constitutive heterochromatin. The three

pos: Alexandrium (dinoflagellate) is controlled through light/dark timing. "Alexandrium" species must be of proper size before then can enter S and G2 phase. (11) "Alexandrium fundyense" increases greatly in size during the G2/M phase and after mitosis, it decreases in size. (12) Other species can produce DNA through the entirety of the cell cycle. (12) Thus, researchers have said that going through G1 is light dependent and going through S phase is size dependent. (11) (12) The specific toxins produced are regulated by the nuclear genes. (3) The genome mass is upwards of 200 pg DNA. (3) It has up to 150 chromosomes

pos: Centrosome cycle cycle occurs early in the cell cycle, so that by the time mitosis occurs there are two centrosomes. The centrosome cycle consists of four phases that are synchronized to cell cycle. These include: centrosome duplication during the G1 phase and S Phase, centrosome maturation in the G2 phase, centrosome separation in the mitotic phase, and centrosome disorientation in the late mitotic phase—G1 phase. Centrioles are generated in new daughter cells through duplication of pre-existing centrioles in the mother cells. Each daughter cell inherits two centrioles (one centrosome) surrounded by pericentriolar material as a result of cell division. The two centrioles

neg: Mitosis Mitosis In cell biology, mitosis () is a part of the cell cycle when replicated chromosomes are separated into two new nuclei. Cell division gives rise to genetically identical cells in which the number of chromosomes is maintained. In general, mitosis (division of the nucleus) is preceded by the S stage of interphase (during which the DNA is replicated) and is often accompanied or followed by cytokinesis, which divides the cytoplasm, organelles and cell membrane into two new cells containing roughly equal shares of these cellular components. Mitosis and cytokinesis together define the mitotic (M) phase of an animal cell

neg: Cell cycle cells. In cells with a nucleus, as in eukaryotes, the cell cycle is also divided into three periods: interphase, the mitotic (M) phase, and cytokinesis. During interphase, the cell grows, accumulating nutrients needed for mitosis, preparing it for cell division and duplicating its DNA. During the mitotic phase, the chromosomes separate. During the final stage, cytokinesis, the chromosomes and cytoplasm separate into two new daughter cells. To ensure the proper division of the 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

neg: Archaea after the cell's chromosome is replicated and the two daughter chromosomes separate, the cell divides. In the genus "Sulfolobus", the cycle has characteristics that are similar to both bacterial and eukaryotic systems. The chromosomes replicate from multiple starting-points (origins of replication) using DNA polymerases that resemble the equivalent eukaryotic enzymes. In euryarchaea the cell division protein FtsZ, which forms a contracting ring around the cell, and the components of the septum that is constructed across the center of the cell, are similar to their bacterial equivalents. In cren- and thaumarchaea, but the cell division machinery Cdv fulfills a similar role.

neg: Chromothripsis which contain whole chromosomes or fragments of chromosomes. The segregation of single chromosomes into individual micronuclei explains why DNA fragmentation is isolated to single chromosomes in chromothripsis. These micronuclei undergo defective DNA replication, which is slower than DNA replication in the main nucleus and causes a proximal DNA damage response (DDR) to be initiated. However, DNA repair and cell cycle checkpoint activation fail to follow. Consequently, chromosomes that are not correctly replicated in micronuclei become fragmented. The method by which the pulverization of these chromosomes occur is not fully understood, but it is thought to be caused either by aberrant

neg: Mitosis of DNA, two circular chromosomes are attached to a special region of the cell membrane, eukaryotic mitosis is usually characterized by the presence of many linear chromosomes, whose kinetochores attaches to the microtubules of the spindle. In relation to the forms of mitosis, closed intranuclear pleuromitosis seems to be the most primitive type, as it is the more similar to bacterial division. Mitotic cells can be visualized microscopically by staining them with fluorescent antibodies and dyes. Mitosis In cell biology, mitosis () is a part of the cell cycle when replicated chromosomes are separated into two new nuclei. Cell division

neg: Cell cycle a spindle. 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 the start of the next. These phases are sequentially known as: Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets in two nuclei. During the process of mitosis the pairs of chromosomes condense and attach to fibers that pull the sister chromatids

neg: Cell cycle coupled processes: karyokinesis, in which the cell's chromosomes are divided, 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 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

neg: Chromosome octamers with part of a DNA strand attached to and wrapped around it). Chromatin fibers are packaged by proteins into a condensed structure called chromatin. Chromatin contains the vast majority of DNA and a small amount inherited maternally, can be found in the mitochondria. Chromatin is present in most cells, with a few exceptions, for example, red blood cells. Chromatin allows the very long DNA molecules to fit into the cell nucleus. During cell division chromatin condenses further to form microscopically visible chromosomes. The structure of chromosomes varies through the cell cycle. During cellular division chromosomes are replicated, divided, and

neg: Homologous recombination and G phases of the cell cycle, when sister chromatids are more easily available. Compared to homologous chromosomes, which are similar to another chromosome but often have different alleles, sister chromatids are an ideal template for homologous recombination because they are an identical copy of a given chromosome. In contrast to homologous recombination, NHEJ is predominant in the G phase of the cell cycle, when the cell is growing but not yet ready to divide. It occurs less frequently after the G phase, but maintains at least some activity throughout the cell cycle. The mechanisms that regulate homologous recombination and

neg: Neuronal cell cycle differentiated, as they are in the adult nervous system. Nevertheless, it remains plausible that neurons may re-enter the cell cycle under certain circumstances. Sympathetic and cortical neurons, for example, try to reactivate the cell cycle when subjected to acute insults such as DNA damage, oxidative stress, and excitotoxicity. This process is referred to as “abortive cell cycle re-entry” because the cells usually die in the G1/S checkpoint before DNA has been replicated. Cell Cycle Regulation Transitions through the cell cycle from one phase to the next are regulated by cyclins binding their respective cyclin dependent kinases (Cdks) which then activate

neg: Chromothripsis DNA replication or by premature chromosome condensation, which entails semi-replicated chromosomes being compacted by cyclin-dependent kinase activity. The resulting fragmented chromosome segments can be joined together to give rise to a rearranged chromosome, which can subsequently be reincorporated into the main nucleus of a daughter cell. The new chromosome can persist for several generations of cell cycle divisions and contribute to the development of a cancer cell. Although the micronucleus model is appropriate, other factors are likely to contribute towards chromothripsis for various cancer genomes. Chromosome shattering is triggered and reassembly of chromosome fragments in close proximity is caused by

neg: Cell cycle checkpoint 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 the cell wall forms a septum which divides the cell into two. As the eukaryotic cell cycle is a complex process, eukaryotes have evolved a

neg: Cohesin anaphase onset, which establishes two sets of identical chromosomes at each pole of the cell (telophase). Then the two daughter cells separate, and a new round of the cell cycle freshly starts in each one, at the stage of G0. 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 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

neg: G1/S transition DNA separation in the M phase. After complete synthesis of its DNA, the cell enters the G2 phase where it continues to grow in preparation for mitosis. Following interphase, the cell transitions into mitosis, containing four sub stages: prophase, anaphase, metaphase, and telophase. In mitosis, DNA condenses into chromosomes, which are lined up and separated by the mitotic spindle. After duplicate DNA is separated on opposite ends of the cell, the cytoplasm of the cell is split in two during cytokinesis resulting in two daughter cells. As with most processes in the body, the cell cycle is highly regulated to

neg: Spindle poison microtubules (polymerized tubulin) that aid, along with regulatory proteins; each other in the activity of appropriately segregating replicated chromosomes. Certain compounds affecting the mitotic spindle have proven highly effective against solid tumors and hematological malignancies. Two specific families of antimitotic agents — vinca alkaloids and taxanes — interrupt the cell’s division by the agitation of microtubule dynamics. The vinca alkaloids work by causing the inhibition of the polymerization of tubulin into microtubules, resulting in the G2/M arrest within the cell cycle and eventually cell death. In contrast, the taxanes arrest the mitotic cell cycle by stabilizing microtubules against depolymerization. Even

neg: Cell division the first time, by Kurt Michelwith, using a phase-contrast microscope. Cell division Cell division is the process by which a parent cell divides into two or more daughter cells. Cell division usually occurs as part of a larger cell cycle. In eukaryotes, there are two distinct types of cell division: a vegetative division, whereby each daughter cell is genetically identical to the parent cell (mitosis), and a reproductive cell division, whereby the number of chromosomes in the daughter cells is reduced by half to produce haploid gametes (meiosis). Meiosis results in four haploid daughter cells by undergoing one round of

neg: Histone H2B the cell cycle. Regular histone H2B is only added to nucleosomes during the S-phase of the cell cycle when DNA is replicated; histone H2B isoforms can be added to nucleosomes at other times during the cell cycle. Histone variants of H2B can be explored using "HistoneDB with Variants" database. Histone H2B is modified by a combination of several types of post-translational modifications. These modifications affect the structural and functional organization of chromatin, and the majority of them are found outside the globular domain of the nucleosome where amino acid residues are more accessible. Possible modifications include acetylation, methylation, phosphorylation, ubiquitination,

neg: Spindle checkpoint phase in the cell cycle have been fulfilled are called checkpoints. All along the cell cycle, there are different checkpoints. The checkpoint ensuring that chromosome segregation is correct is termed spindle assembly checkpoint (SAC), spindle checkpoint or mitotic checkpoint. During mitosis or meiosis, the spindle checkpoint prevents anaphase onset until all chromosomes are properly attached to the spindle. To achieve proper segregation, the two kinetochores on the sister chromatids must be attached to opposite spindle poles (bipolar orientation). Only this pattern of attachment will ensure that each daughter cell receives one copy of the chromosome. When cells are ready to

neg: Gametophyte Gametophyte A gametophyte () is one of the two alternating phases in the life cycle of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has one set of chromosomes. The gametophyte is the sexual phase in the life cycle of plants and algae. It develops sex organs that produce gametes, haploid sex cells that participate in fertilization to form a diploid zygote which has two sets of chromosomes. Cell division of the zygote results in a new diploid multicellular organism, the second stage in the life cycle known as the sporophyte, the

neg: Meiosis 1c). Prophase I is typically the longest phase of meiosis. During prophase I, homologous chromosomes pair and exchange DNA (homologous recombination). This often results in chromosomal crossover. This process is critical for pairing between homologous chromosomes and hence for accurate segregation of the chromosomes at the first meiosis division. The new combinations of DNA created during crossover are a significant source of genetic variation, and result in new combinations of alleles, which may be beneficial. The paired and replicated chromosomes are called bivalents or tetrads, which have two chromosomes and four chromatids, with one chromosome coming from each parent. The

neg: CHEK1 other cell cycle stages. During this phase the Chk1 activating element of ssDNA can not be generated suggesting an alternate form of activation. Studies on Chk1 deficient chicken lymphoma cells have shown increased levels of genomic instability and failure to arrest during the spindle checkpoint phase in mitosis. Furthermore, haploinsufficient mammary epithelial cells illustrated misaligned chromosomes and abnormal segregation. These studies suggest Chk1 depletion can lead to defects in the spindle checkpoint resulting in mitotic abnormalities. DNA damage induces the activation of Chk1 which facilitates the initiation of the DNA damage response (DDR) and cell cycle checkpoints. The DNA damage

neg: Mitotic inhibitor 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 fungus, respectively. Cytogenetics, the study of chromosomal material by analysis of G-Banded chromosomes, uses mitotic inhibitors extensively. In order to prepare a slide for cytogenetic study, a mitotic inhibitor is added to the cells being studied. This

neg: Proliferative index cycle-associated proteins. Mitotic indexing is the oldest method of assessing proliferation and is determined by counting the number of mitotic figures (cells undergoing mitosis) through a light microscope on H&E stained sections. It is usually expressed as the number of cells per microscopic field. Cells in the mitotic phase are identified by the typical appearance of their chromosomes in the cell during the mitotic phase of the cell cycle. Usually the number of mitotic figures is expressed as the total number in a defined number of high power fields, such as 10 mitoses in 10 high power fields. Since the

neg: Pre-replication complex MCM10. MCM10 cooperates with MCM2-7 in the recruitment of Cdc45. Cdc45 then recruits key components of the replisome; the replicative DNA polymerase α and its primase. DNA replication can then begin. During each cell cycle, it is important that the genome be completely replicated once and only once. Formation of the pre-replication complex during late M and early G1 phase is required for genome replication, but after the genome has been replicated the pre-RC must not form again until the next cell cycle. In S. cerevisiae, CDKs prevent formation of the replication complex during late G1, S, and G2 phases

neg: Clb 5,6 (Cdk1) mutational studies targeting the Clb5 and Clb6 encoding genes have shown that both can activate origins usually replicated early in the cell cycle, but only Clb5 can activate late-stage origins. In cells without Clb5, S-phase is extended because late-stage origins are required to be replicated through the gradual spread of replication forks rather than Clb5-stimulated replication. Cells without Clb6 have little to no phenotypic changes since Clb5 can activate both types of origins. In double mutants for Clb5 and Clb6, the onset of S-phase (rather than the length) is significantly delayed, but will eventually occur as a side result of

neg: Histone This involves the wrapping of DNA around nucleosomes with approximately 50 base pairs of DNA separating each pair of nucleosomes (also referred to as linker DNA). Higher-order structures include the 30 nm fiber (forming an irregular zigzag) and 100 nm fiber, these being the structures found in normal cells. During mitosis and meiosis, the condensed chromosomes are assembled through interactions between nucleosomes and other regulatory proteins. Histones are subdivided into canonical replication-dependent histones that are expressed during the S-phase of cell cycle and replication-independent histone variants, expressed during the whole cell cycle. In animals, genes encoding canonical histones are typically

neg: Cell division the chromosomes line up in the middle of the cell by MTOCs ( microtubule organizing center) by pushing and pulling on centromeres of both chromatids which causes the chromosome to move to the center. The chromosomes are still condensing and are currently at one step away from being the most coiled and condensed they will be. spindle fibre and have already connected to the kinetochores. At this point, the chromosomes are ready to split into opposite poles of the cell towards the spindle to which they are connected. Anaphase is a very short stage of the cell cycle and occurs

neg: Sporophyte Sporophyte A sporophyte () is the diploid multicellular stage in the life cycle of a plant or alga. It develops from the zygote produced when a haploid egg cell is fertilized by a haploid sperm and each sporophyte cell therefore has a double set of chromosomes, one set from each parent. All land plants, and most multicellular algae, have life cycles in which a multicellular diploid sporophyte phase alternates with a multicellular haploid gametophyte phase. In the seed plants, ("gymnosperms") and flowering plants ("angiosperms"), the sporophyte phase is more prominent than the gametophyte, and is the familiar green plant with

neg: Cell nucleus in open mitosis, the cell divides to form two cells. In order for this process to be possible, each of the new daughter cells must have a full set of genes, a process requiring replication of the chromosomes as well as segregation of the separate sets. This occurs by the replicated chromosomes, the sister chromatids, attaching to microtubules, which in turn are attached to different centrosomes. The sister chromatids can then be pulled to separate locations in the cell. In many cells, the centrosome is located in the cytoplasm, outside the nucleus; the microtubules would be unable to attach to

neg: Insertional mutagenesis gene is normally turned off in the cell; however when it is turned on it is able to push the cell into the G1 phase of the cell cycle and cause the cell to begin replication, causing unchecked cell proliferation while allowing the viral gene to be replicated. After many replications where the viral gene stays latent tumours begin to grow. These tumours are normally derived from one mutated/transformed cell (clonal in origin). Avian leukosis virus is an example of a virus that causes a disease by insertional mutagenesis. Newly hatched chicks infected with Avian leukosis virus will begin to

neg: Hayflick limit proliferating; Hayflick called this the time of "luxuriant growth". After months of doubling the cells eventually reach phase three, a phenomenon he named "senescence", where cell replication rate slows before halting altogether. The Hayflick limit has been found to correlate with the length of the telomeric region at the end of chromosomes. During the process of DNA replication of a chromosome, small segments of DNA within each telomere are unable to be copied and are lost. This occurs due to the uneven nature of DNA replication, where leading and lagging strands are not replicated symmetrically. The telomeric region of DNA

neg: Replication timing Replication timing Replication timing refers to the order in which segments of DNA along the length of a chromosome are duplicated. In eukaryotic cells (cells that package their DNA within a nucleus), chromosomes consist of very long linear double-stranded DNA molecules. During the S-phase of each cell cycle (Figure 1), all of the DNA in a cell is duplicated in order to provide one copy to each of the daughter cells after the next cell division. The process of duplicating DNA is called DNA replication, and it takes place by first unwinding the duplex DNA molecule, starting at many locations

neg: Sister chromatids Sister chromatids A sister chromatid refers to the identical copies (chromatids) formed by the DNA replication of a chromosome, with both copies joined together by a common centromere. In other words, a sister chromatid may also be said to be 'one-half' of the duplicated chromosome. A pair of sister chromatids is called a dyad. A full set of sister chromatids is created during the synthesis (S) phase of interphase, when all the chromosomes in a cell are replicated. The two sister chromatids are separated from each other into two different cells during mitosis or during the second division of meiosis.

neg: Prophase Prophase Prophase (from the Greek πρό, "before" and φάσις, "stage") is the first stage of cell division in both mitosis and meiosis. Beginning after interphase, DNA has already been replicated when the cell enters prophase. The main occurrences in prophase are the condensation of the chromatin and the disappearance of the nucleolus. Microscopy can be used to visualize condensed chromosomes as they move through meiosis and mitosis. Various DNA stains are used to treat cells such that condensing chromosomes can be visualized as the move through prophase. The giemsa G-banding technique is commonly used to identify mammalian chromosomes, utilizing the

neg: Acute radiation syndrome likely to be repaired. Somatic mutations cannot be passed down from parent to offspring, but these mutations can propagate in cell lines within an organism. Radiation damage can also cause chromosome and chromatid aberrations, and their effect depends on what stage of the mitotic cycle the cell is currently in when the irradiation occurs. If the cell is in interphase, while it is still a single strand of chromatin, the damage will be replicated during the S1 phase of cell cycle, and there will be a break on both chromosome arms. Then the damage will be apparent in both daughter

neg: Okazaki fragments cells can take up to 400 hours. Eukaryotes also have a distinct operation for replicating the telomeres at the end of their last chromosomes. Prokaryotes have circular chromosomes, causing no ends to synthesize. Prokaryotes have a short replication process that occurs continuously; eukaryotic cells, on the other hand, only undertake DNA replication during the S-phase of the cell cycle. The similarities are the steps for the DNA replication. In both prokaryotes and eukaryotes, replication is accomplished by unwinding the DNA by an enzyme called the DNA helicase. New strands are created by enzymes called DNA polymerases. Both of these follow

neg: Angelika Amon continues until reactivation of CDC28 toward the end of G1. The Amon lab primarily investigates yeast ("Saccharomyces cerevisiae") as a model for understanding the controls that govern cell-cycle progression. As a Whitehead Fellow, her team discovered that CDC20 plays a crucial role in cell division. Her Whitehead team identified an interaction between phosphatase and CDC14 which initiates the exit of cells from mitosis to the G1 phase. Amon's team demonstrated that CDC20 is the target protein in the spindle checkpoint during mitosis. Amon's more recent work has investigated the regulation of chromosome segregation and how chromosomes are accurately transmitted to

neg: Prophase the meiotic recombination checkpoint) that prevent the cell from entering metaphase I with errors due to recombination. Prophase Prophase (from the Greek πρό, "before" and φάσις, "stage") is the first stage of cell division in both mitosis and meiosis. Beginning after interphase, DNA has already been replicated when the cell enters prophase. The main occurrences in prophase are the condensation of the chromatin and the disappearance of the nucleolus. Microscopy can be used to visualize condensed chromosomes as they move through meiosis and mitosis. Various DNA stains are used to treat cells such that condensing chromosomes can be visualized as

neg: Cell division Cell division Cell division is the process by which a parent cell divides into two or more daughter cells. Cell division usually occurs as part of a larger cell cycle. In eukaryotes, there are two distinct types of cell division: a vegetative division, whereby each daughter cell is genetically identical to the parent cell (mitosis), and a reproductive cell division, whereby the number of chromosomes in the daughter cells is reduced by half to produce haploid gametes (meiosis). Meiosis results in four haploid daughter cells by undergoing one round of DNA replication followed by two divisions. Homologous chromosomes are separated

neg: Boring Billion in the amount of genetic material inside cells as eukaryotes were evolving, the evolution of entirely new structures and mechanisms of gene copying was required, leading to the development of the eukaryotic cell cycle. Histones likely appeared during the Boring Billion to help organize the increasing amount of DNA in ancestral eukaryotic cells. DNA was packed by histones into the first chromosomes. A system of more rapid eukaryotic DNA replication in which DNA was replicated from multiple replication origins was developed so that cells containing much more genetic material would still be able to reproduce quickly. The development of an

neg: Chromatin bridge may form by any number of processes wherein chromosomes remain topologically entangled during mitosis. One way in which this may occur is the failure to resolve joint molecules formed during homologous recombination mediated DNA repair, a process that ensures that replicated chromosomes are intact before chromosomes are segregated during cell division. In particular, genetic studies have demonstrated that the loss of the enzymes BLM (Bloom's Syndrome Helicase) or FANCM each result in a dramatic increase in the number of chromatin bridges. This occurs because loss of these genes causes an increase in chromosome fusions, either in an end-to-end manner or

neg: Replication timing with relative ease indicates that we will soon have a wealth of information about where and when large changes in chromosome folding occur during development and in different diseases. Replication timing Replication timing refers to the order in which segments of DNA along the length of a chromosome are duplicated. In eukaryotic cells (cells that package their DNA within a nucleus), chromosomes consist of very long linear double-stranded DNA molecules. During the S-phase of each cell cycle (Figure 1), all of the DNA in a cell is duplicated in order to provide one copy to each of the daughter cells

neg: Prophase centrosomes, the formation of the mitotic spindle, and the beginning of nucleoli break down. DNA that was replicated in interphase is condensed from molecules with lengths reaching 4 cm to chromosomes that are measured in micrograms. This process employs the condensin complex. Condensed chromosomes consist of two sister chromatids joined at the centromere. During prophase in animal cells, centrosomes move far enough apart to be resolved using a light microscope. Microtubule activity in each centrosome is increased due to recruitment of γ-tubulin. Replicated centrosomes from interphase move apart towards opposite poles of the cell, powered by centrosome associated motor proteins.

neg: Replication timing geography is established in each newly formed cell, the chromosome domains do not move appreciably until the next cell division. In all multi-cellular organisms where it has been measured, early replication takes place in the interior of the nucleus and the chromatin around the periphery is replicated later. Recently developed methods to measure the points where different parts of chromosomes touch each other are almost perfectly aligned to when they replicate. In other words, regions that are replicated early versus late are packaged in such a way as to be spatially segregated in the nucleus, with the intervening DNA containing

neg: Clb 5,6 (Cdk1) the buildup of other mitotic cyclins (Clb1-4). S-phase length is normal in these double mutants. Similar studies have shown a significant difference between mitosis and meiosis progression in cells lacking Clb5 or Clb6, primarily that meiosis S-phase cannot occur properly without Clb5. These mutant cells segregate their unreplicated DNA, which is lethal, and fail to activate the MEC1-DNA M-phase checkpoint, which usually inhibits cell cycle progression if DNA has not been replicated. The inability of Clb1-4 to compensate for the lack of Clb5 activity could potentially be explained by timing and accumulation arguments. In this hypothesis, cyclin concentrations must rise

neg: Cell division cycle 7-related protein kinase (Cdc6 and Cdt1). Mitosis occurs during M phase of the cell cycle and has a number of stages; telophase is the end stage of mitosis when the replication of chromosomes is complete, but separation has not occurred. The Cdc7/Dbf4 kinase complex, along with another serine-threonine kinase, cyclin-dependent kinase (Cdk), phosphorylates the pre-RC which activates it at the G1/S transition. The Dbf4 tethers itself to part of the pre-RC, the origin recognition complex (ORC). Since Cdc7 is attached to the Dbf4 protein the entire complex is held in place during replication. This activation of MCM 2 leads to helicase activity of

neg: DNA damage (naturally occurring) chromosomes compared with cells that are able to undergo a full G2 arrest, suggesting that the purpose of the delay is to give the cell time to repair damaged chromosomes before continuing with the cell cycle. This ensures the proper functioning of mitosis. Various species of animals exhibit similar mechanisms of cellular delay in response to DNA damage, which can be caused by exposure to x-irradiation. The budding yeast Saccharomyces cerevisiae has specifically been studied because progression through the cell cycle can be followed via nuclear morphology with ease. By studying Saccharomyces cerevisiae, researchers have been able to learn more

neg: Anaphase Anaphase 'Anaphase' (from the Greek ἀνά, "up" and φάσις, "stage"), is the stage of mitosis after the metaphase when replicated chromosomes are split and the daughter chromatids are moved to opposite poles of the cell. Chromosomes also reach their overall maximum condensation in late anaphase, to help chromosome segregation and the re-formation of the nucleus. Anaphase starts when the anaphase promoting complex marks an inhibitory chaperone called securin with ubiquitin for destruction. Securin is a protein which inhibits a protease known as separase. The destruction of securin unleashes separase which then breaks down cohesin, a protein responsible for holding sister

neg: Plasmid that may be replicated in the nucleus. Viruses are the most common examples of this, such as herpesviruses, adenoviruses, and polyomaviruses, but some are plasmids. Other examples include aberrant chromosomal fragments, such as double minute chromosomes, that can arise during artificial gene amplifications or in pathologic processes (e.g., cancer cell transformation). Episomes in eukaryotes behave similarly to plasmids in prokaryotes in that the DNA is stably maintained and replicated with the host cell. Cytoplasmic viral episomes (as in poxvirus infections) can also occur. Some episomes, such as herpesviruses, replicate in a rolling circle mechanism, similar to bacterial phage viruses. Others

neg: Circular bacterial chromosome circular chromosomes can sometimes remain interlinked or tangled, and they must be resolved so that each cell inherits one complete copy of the chromosome during cell division. Bacterial chromosome replication is best understood in the well-studied bacteria "Escherichia coli" and "Bacillus subtilis". Chromosome replication proceeds in three major stages: initiation, elongation and termination. The initiation stage starts with the ordered assembly of "initiator" proteins at the origin region of the chromosome, called oriC. These assembly stages are regulated to ensure that chromosome replication occurs only once in each cell cycle. During the elongation phase of replication, the enzymes that were

neg: Cell nucleus aging in its sufferers. The exact mechanism by which the associated biochemical changes give rise to the aged phenotype is not well understood. The cell nucleus contains the majority of the cell's genetic material in the form of multiple linear DNA molecules organized into structures called chromosomes. Each human cell contains roughly two meters of DNA. During most of the cell cycle these are organized in a DNA-protein complex known as chromatin, and during cell division the chromatin can be seen to form the well-defined chromosomes familiar from a karyotype. A small fraction of the cell's genes are located instead

neg: Cell cycle analysis phase, and in the G phase and M phase (after S) identifies the cell cycle phase position in the major phases (G/G versus S versus G/M phase) of the cell cycle. The cellular DNA content of individual cells is often plotted as their frequency histogram to provide information about relative frequency (percentage) of cells in the major phases of the cell cycle. Cell cycle anomalies revealed on the DNA content frequency histogram are often observed after different types of cell damage, for example such DNA damage that interrupts the cell cycle progression at certain checkpoints. Such an arrest of the

neg: Chromatid Chromatid A chromatid (Greek "khrōmat-" 'color' + "-id") is one copy of a newly copied chromosome which is still joined to the original chromosome by a single centromere. Before replication, one chromosome is composed of one DNA molecule. Following replication, each chromosome is composed of two DNA molecules; in other words, DNA replication itself increases the amount of DNA but does "not" increase the number of chromosomes. The two identical copies—each forming one half of the replicated chromosome—are called chromatids. During the later stages of cell division these chromatids separate longitudinally to become individual chromosomes. Chromatid pairs are normally genetically

neg: Genome If the DNA is replicated faster than the bacterial cells divide, multiple copies of the chromosome can be present in a single cell. Most prokaryotes have very little repetitive DNA in their genomes. However, some symbiotic bacteria (e.g. "Serratia symbiotica") have reduced genomes and a high fraction of pseudogenes: only ~40% of their DNA encodes proteins. Some bacteria have auxiliary genetic material, which is carried in plasmids. Eukaryotic genomes are composed of one or more linear DNA chromosomes. The number of chromosomes varies widely from Jack jumper ants and an asexual nemotode, which each have only one pair, to a

neg: Vinblastine established protocols of the Histiocytosis Association. Adverse effects of vinblastine include hair loss, loss of white blood cells and blood platelets, gastrointestinal problems, high blood pressure, excessive sweating, depression, muscle cramps, vertigo and headaches. Vinblastine is a "vinca" alkaloid and a chemical analogue of vincristine. It binds tubulin, thereby inhibiting the assembly of microtubules. Vinblastine treatment causes M phase specific cell cycle arrest by disrupting microtubule assembly and proper formation of the mitotic spindle and the kinetochore, each of which are necessary for the separation of chromosomes during anaphase of mitosis. Toxicities include bone marrow suppression (which is dose-limiting), gastrointestinal