M-Mitosis phase

Eucaryotic cells execute their reproduction in a cyclic process, in which at least two phases, a S phase and a M phase, can be differentiated on the basis of biochemical and morphological features. The biochemical characteristic of the S (synthesis) phase is the replication of nuclear DNA and thus doubling of the genetic information. In M (mitosis) phase, division of the chromosomes between the daughter cells is prepared and carried out. 

Because MIB-1 monoclonal antibody is used extensively to determine the cell proliferation index, its applications are discussed below. This antibody detects the nuclear antigen Ki-67 expressed in proliferating cells but not in resting cells. The antibody reacts with the nuclei of cells in mid-Gj (first gap), S (DNA synthesis), G2 (second gap), and M (mitosis) phases, but not in the G0 or quiescent phases. The use of MIB-1 antibody is one of the simplest and most reliable labeling techniques for assessing the rate of proliferation of a neoplastic cell population. Thus, the antibody can be used to assess the growth fraction (i.e., the number of cells in cell cycle) of normal, reactive, and neoplastic tissues. 

Hg. 6.1 Cell cycle and regulation of cell cycle progression by cyclin-dependent kinases [3]. Cl, Capi phase between M and S phases S, DNA synthesis phase G2 gap 2 phase between S and M phases and M, mitosis phase. 

During the M (mitosis) phase, cell division occurs. 

S—DNA replication phase Gj—Resting phase Gj—Resting phase M—Mitosis phase... 

The cell cycle is a key process that recurs in a periodic manner. Early cell cycles in amphibian embryos are driven by a mitotic oscillator. This oscillator produces the repetitive activation of the cyclin-dependent kinase cdkl, also known as cdc2 [131]. Cyclin synthesis is sufficient to drive repetitive cell division cycles in amphibian embryonic cells [132]. The period of these relatively simple cell cycles is of the order of 30 min. In somatic cells the cell cycle becomes longer, with durations of up to 24 h or more, owing to the presence of checkpoints that ensure that a cell cycle phase is properly completed before the cell progresses to the next phase. The cell cycle goes successively through the phases Gl, S (DNA replication), G2, and M (mitosis) before a new cycle starts in Gl. After mitosis cells can also enter a quiescent phase GO, from which they enter Gl under mitogenic stimulation. 

Fig. 9. The cell cycle. M mitosis G1+S+G2 interphase, i.e., the period between ceU division. During G1 (G for gap) the cellular genome is in the diploid state. This is followed by the S-phase (S for synthesis) during which the DNA is replicated, and finally G2. Insert Cell-cycle analysis of HM02 cells cultured with and without vinblastine. CeU-cycle distribution was determined by staining DNA with propidium iodide, and the number of cells in different phases of the cell cycle was measured with a FACStar flow cytometer. Vinblastine, which disrupts the formation of microtubules, causes cell-cycle arrest in the G2/M-phase...

The cell cycle consists of four successive phases along which the cell progresses Gl, S (DNA replication), G2, and M (mitosis). 

Of the four phases, the two critical ones are DNA replication, which occurs during Gi to S phase, and the physical process of cell division, which occurs during G2 to M (for mitosis) phase these are critical checkpoints . 

Figure 37.2 A simplified schematic view of cell cycle progression in diatoms, with critical arrest points and dominant processes indicated. Most diatoms arrest at the Gl/S boundary, but a secondary arrest point can occur during the G2/M phase. M mitosis S DNA replication (synthesis) G1 and G2 gap phases.

Figure 1 Phases of the cell cycle. Go, resting phase (nonproliferation of cells) Gi, pre-DNA synthetic phase (12h to a few days). S, DNA synthesis (usually 2-4 h) Ga, post-DNA synthesis (2-4h cells are tetraphoid in this stage) M, mitosis (1-2 h).

Figure 3-1. Cell cycle. (Gj = cell growth S = DNA synthesis and replication Gj = proteins made in preparation for cell division M = mitosis G = rest phase.)...

The eukaryote cell cycle is composed of the following four phases M phase, mitosis phase (gap 1), between mitosis and initiation of DNA synthesis S phase, DNA synthesis and phase (gap 2), cell growth and macromolecule synthesis. 

Shortly after acute renal failure many normally quiescent kidney cells enter the cell cyde. Orderly progression through the cell cycle is regulated by sequential synthesis, activation, compartmentalization and degradahon of proteins controUing both entry and exit from each of the four phases of the cyde G1 (gap-1), S (DNA synthesis), G2 (gap-2) and M (mitosis) (Figure... 

The eukaryotic cell cycle is divided into four phases M (mitosis), Gj (the period between mitosis and the Initiation of nuclear DNA replication), S (the period of nuclear DNA replication), and G2 (the period between the completion of nuclear DNA replication and mitosis) (see Figure 21-1). 

Cell biologists consider the cell cycle to be divided into five phases Gl, S, G2, M and GO. There are three principal checkpoints at which the cell cycle is stopped if defects are detected the Gl checkpoint, the G2 checkpoint and the spindle checkpoint during the mitosis phase. The tumour suppressors p53, the guardian angel protein , and Rh protein regulate progression from the Gl phase to the S phase. Mutations of p53 and Rb that fail to suppress progression result in uncontrolled cell division, i.e. tumour development. 

Mitosis phase (M phase). The spindle checkpoint ensures that all the chromosomes are correctly aligned on the spindle fibre prior to... 

Fig. 2.1. Duration of phases of the cell cycle in the apical meristem of Vida fabci at 19°. Values in parentheses indicate duration of each phase in h. M mitosis Gj period between division and the onset of S S period of DNA synthesis (DNA content doubles) G2 period between termination of DNA synthesis and initiation of mitosis (organization of newly synthesized DNA into chromosomes). Total cycle time = 19.3 h. (After Evans and Scott 1964)...

The eukaryotic somatic cell cycle is defined by a sequential order of tasks a dividing cell has to complete it must replicate its DNA, segregate its chromosomes, grow, and divide. The cell cycle can be divided into four discrete phases. DNA replication is restricted to S phase (DNA synthesis phase), which is preceded by a gap phase called G1 and followed by a gap phase called G2. During mitosis (M phase) the sister chromatids are segregated into two new daughter nuclei and mitosis is completed by the division of the cytoplasm termed cytokinesis (Fig. 1). 

APC is active from mid-M phase (anaphase) to the end of G1 phase and required for disconnecting sister chromatids and exit from M-Phase to Gl. The complex mediates the ubiquitination of Securin and Cyclin B. Degradation of these proteins, which block mitotic progression, promotes anaphase onset and exit from mitosis. 

Enoch, T., and Nurse, P. (1991). Coupling M phase and S phase controls maintaining the dependence of mitosis on chromosome replication. Cell 65 921-923. 

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