CELL DIVISION is the process by which a parent cell divides into two
or more daughter cells.
For simple unicellular organisms such as the amoeba , one cell division is equivalent to reproduction – an entire new organism is created. On a larger scale, mitotic cell division can create progeny from multicellular organisms, such as plants that grow from cuttings. Mitotic cell division enables sexually reproducing organisms to develop from the one-celled zygote , which itself was produced by meiotic cell division from gametes . After growth, cell division by mitosis allows for continual construction and repair of the organism. The human body experiences about 10 quadrillion cell divisions in a lifetime.
The primary concern of cell division is the maintenance of the original cell's genome . Before division can occur, the genomic information that is stored in 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.
* 1 Phases of cell division
* 2 Variants * 3 Degradation * 4 See also * 5 Notes * 6 References * 7 Further reading * 8 External links
PHASES OF CELL DIVISION
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Interphase is the process a cell must go through before mitosis, meiosis, and cytokinesis. Interphase consists of four main stages: G1, S, and G2. G1 is a time of growth for the cell. If the cell does not progress through G1, the cell then enters a stage called G0. In G0, cells are still living but they are put on hold. The cells may later be called back into interphase if needed at a later time. There are checkpoints during interphase that allow the cell to be either progressed or denied further development. In S phase, the chromosomes are replicated in order for the genetic content to be maintained. During G2, the cell undergoes the final stages of growth before it enters the M phase. The M phase, can be either mitosis or meiosis depending on the type of cell. Germ cells undergo meiosis, while somatic cells will undergo mitosis. After the cell proceeds through 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. 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.
Metaphase is the stage in cell division when the chromosomes line up in the middle of the cell. The chromosomes are still condensing and are currently at one step away from being the most coiled and condensed they will be. Spindle and spindle fibers 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.
Telophase is the last stage of the cell cycle. Two cells form around the chromatin at the two poles of the cell. Two nuclear membranes begin to reform and the chromatin begin to unwind.
Image of the mitotic spindle in a human cell showing microtubules in green, chromosomes (DNA) in blue, and kinetochores in red.
CELLS are broadly classified into two main categories: simple,
non-nucleated prokaryotic cells, and complex, nucleated eukaryotic
cells. Owing to their structural differences, eukaryotic and
prokaryotic cells do not divide in the same way. Also, the pattern of
cell division that transforms eukaryotic stem cells into gametes
(sperm cells in males or egg cells in females), termed meiosis, is
different from that of the division of somatic cells in the body.
Multicellular organisms replace worn-out cells through cell division.
In some animals, however, cell division eventually halts. In humans
this occurs, on average, after 52 divisions, known as the Hayflick
limit . The cell is then referred to as senescent . Cells stop
dividing because the telomeres , protective bits of DNA on the end of
a chromosome required for replication, shorten with each copy,
eventually being consumed.
* ^ Single-celled organisms. See introduction of the article on microorganisms .
* ^ Robert.S Hine, ed. (2008). Oxford Dictionary Biology (6th ed.). New York: Oxford University Press. p. 113. ISBN 978-0-19-920462-5 . * ^ Griffiths, Anthony J.F.; Wessler, Susan R.; Carroll, Sean B.; Doebley, John (2012). Introduction to Genetic Analysis (10 ed.). New York: W.H. Freeman and Company. p. 35. ISBN 978-1-4292-2943-2 . * ^ Maton, Anthea (1997). Cells: Building Blocks of Life. New Jersey: Prentice Hall. pp. 70–74. ISBN 0-13-423476-6 . * ^ Quammen, David (April 2008). "Contagious cancer: The evolution of a killer". Harper's. 316 (1895): 42. Retrieved 24 September 2012. * ^ Marieb, Elaine (2000). Essentials of human anatomy and physiology. San Francisco: Benjamin Cummings. ISBN 0-8053-4940-5 . * ^ Schermelleh, Lothar; Carlton, Peter M.; Haase, Sebastian; Shao, Lin; Winoto, Lukman; Kner, Peter; Burke, Brian; Cardoso, M. Cristin; Agard, David A. (2008-06-06). "Subdiffraction Multicolor Imaging of the Nuclear Periphery with 3D Structured Illumination Microscopy" . Science. 320 (5881): 1332–1336. ISSN 0036-8075 . PMC 2916659 . PMID 18535242 . doi :10.1126/science.1156947 . * ^ "Researchers Shed Light On Shrinking Of Chromosomes". ScienceDaily. June 12, 2007. Retrieved 2017-02-02. * ^ "The Cell Cycle". www.biology-pages.info. Retrieved 2017-02-02.
* ^ Hetzer, Martin W. (2017-02-02). "The Nuclear Envelope" . Cold Spring Harbor Perspectives in Biology. 2 (3). ISSN 1943-0264 . PMC 2829960 . PMID 20300205 . doi :10.1101/cshperspect.a000539 . * ^ Phase Holographic Imaging. Cell Division
* Morgan HI. (2007). "The Cell Cycle: Principles of Control" London: New Science Press. * J.M.Turner Fetus into Man (1978, 1989). Harvard University Press. ISBN 0-674-30692-9 * Cell division: binary fission and mitosis