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Cell division is the process by which a parent cell divides into two or more daughter cells.[1] Cell division usually occurs as part of a larger cell cycle. In eukaryotes, there are two distinct types of cell division; an asexual reproduction, whereby each daughter cell is genetically identical to the parent cell (mitosis), that are diploid cells [1]and a reproductive cell division, whereby the number of chromosomes in the daughter cells is reduced by half to produce haploid gametes (meiosis).[2] In cell biology, mitosis (/maɪˈtoʊsɪs/) is a part of the cell cycle, in which, replicated chromosomes are separated into two new nuclei. Mitosis produces genetically identical cells in which the total number of chromosomes is maintained. In general, mitosis (division of the nucleus) is preceded by the G1 stage of interphase, and is often followed by cytokinesis; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. The different stages of Mitosis all together define the mitotic (M) phase of an animal cell cycle—once the parent cell is divided in the mitotic phase, it develops two identical daughter cells [3]. Meiosis results in four haploid daughter cells by undergoing one round of DNA replication followed by two divisions. Homologous chromosomes are separated in the first division, and sister chromatids are separated in the second division. Both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. Both are believed to be present in the last eukaryotic common ancestor.

Prokaryotes (bacteria and archaea) usually undergo an asexual cell division known as binary fission, where their genetic material is divided equally into two daughter cells. While binary fission may be the means of division by most prokaryotes, there are alternative manners of division, such as budding, that have been observed. All cell divisions, regardless of organism, are preceded by a single round of DNA replication.

Interphase[edit]

Interphase is the process through which a cell must go before mitosis, meiosis, and cytokinesis.[4] Interphase consists of three main phases: 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.[5] There are checkpoints during interphase that allow the cell to either advance or halt further development. One of the checkpoint is between G1 and S, the purpose for this checkpoint is to check for appropriate cell size and any DNA damage. The second check point is in the G2 phase, this checkpoint also check for cell size but also the DNA replication. The last check point is located at the site of metaphase, where it checks that the chromosomes are correctly connected to the mitotic spindles. [6]In S phase, the chromosomes are replicated in order for the genetic content to be maintained.[7] During G2, the cell undergoes the final stages of growth before 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 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.[8] There are three transition checkpoints the cell has to go through before entering the M phase. The most important being the G1-S transition checkpoint. If the cell does not pass this checkpoint, it results in the cell exiting the cell cycle.[9]

Prophase[edit]

Image of prophase, of a roots of Vicia faba.

Prophase is the first stage of division. The nuclear envelope is broken down in this stage, long strands of chromatin condense to form shorter more visible strands called chromosomes, the nucleolus disappears, and microtubules attach to the chromosomes at the disc-shaped kinetochores present in the centromere.[10] Microtubules associated with the alignment and separation of chromosomes are referred to as the spindle and spindle fibers. Chromosomes will also be visible under a microscope and will be connected at the centromere. During this condensation and alignment period in meiosis, the homologous chromosomes undergo a break in their double-stranded DNA at the same locations, followed by a recombination of the now fragmented parental DNA strands into non-parental combinations, known as crossing over.[11] This process is evidenced to be caused in a large part by the highly conserved Spo11 protein through a mechanism similar to that seen with toposomerase in DNA replication and transcription.[12]

  1. ^ Martin EA, Hine R (2020). A dictionary of biology (6th ed.). Oxford: Oxford University Press. ISBN 9780199204625. OCLC 176818780.
  2. ^ Griffiths AJ (2012). Introduction to genetic analysis (10th ed.). New York: W.H. Freeman and Co. ISBN 9781429229432. OCLC 698085201.
  3. ^ "10.2 The Cell Cycle - Biology 2e | OpenStax". openstax.org. Retrieved 2020-11-24.
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  6. ^ Molinari, M. (2000). "Cell cycle checkpoints and their inactivation in human cancer". Cell Proliferation. 33 (5): 261–274. doi:10.1046/j.1365-2184.2000.00191.x. ISSN 1365-2184. PMC 6496592. PMID 11063129.{{cite journal}}: CS1 maint: PMC format (link)
  7. ^ Morgan DO (2007). The cell cycle : principles of control. London: New Science Press. ISBN 9780199206100. OCLC 70173205.
  8. ^ Lindqvist A, van Zon W, Karlsson Rosenthal C, Wolthuis RM (May 2007). "Cyclin B1-Cdk1 activation continues after centrosome separation to control mitotic progression". PLOS Biology. 5 (5): e123. doi:10.1371/journal.pbio.0050123. PMC 1858714. PMID 17472438.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  9. ^ Paulovich AG, Toczyski DP, Hartwell LH (February 1997). "When checkpoints fail". Cell. 88 (3): 315–21. doi:10.1016/S0092-8674(00)81870-X. PMID 9039258. S2CID 5530166.
  10. ^ Schermelleh L, Carlton PM, Haase S, Shao L, Winoto L, Kner P, Burke B, Cardoso MC, Agard DA, Gustafsson MG, Leonhardt H, Sedat JW (June 2008). "Subdiffraction multicolour imaging of the nuclear periphery with 3D structured illumination microscopy". Science. 320 (5881): 1332–6. Bibcode:2008Sci...320.1332S. doi:10.1126/science.1156947. PMC 2916659. PMID 18535242.
  11. ^ Lewontin RC, Miller JH, Gelbart WM, Griffiths AJ (1999). "The Mechanism of Crossing-Over". Modern Genetic Analysis.
  12. ^ Keeney S (2001). Mechanism and control of meiotic recombination initiation. Current Topics in Developmental Biology. Vol. 52. Elsevier. pp. 1–53. doi:10.1016/s0070-2153(01)52008-6. ISBN 9780121531522. PMID 11529427.
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