Cell division
 |
This includes a list of references, but its sources remain unclear because it has insufficient inline citations. (August 2007) |
Cell division is the York|isbn=978-1-4292-2943-8|pages=35|author=Griffiths, Anthony J.F.|edition=10|coauthors=Wessler, Susan R., Carroll, Sean B., Doebley, John}}</ref> and a reductive cell division, whereby the number of chromosomes in the daughter cells is reduced by half, to produce haploid gametes (meiosis). Both of these cell division cycles are required in sexually reproducing organisms at some point in their life cycle, and both are believed to be present in the last eukaryotic common ancestor[1] Prokaryotes also undergo a vegetative cell division known as binary fission, where their genetic material is segregated equally into two daughter cells. All cell divisions, regardless of organism, are preceded by a single round of DNA replication.
For simple unicellular organisms[Note 1] 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. Cell division also enables sexually reproducing organisms to develop from the one-celled zygote, which itself was produced by cell division from gametes. And after growth, cell division allows for continual construction and repair of the organism.[2] A human being's body experiences about 10,000 trillion cell divisions in a lifetime.[3]
Cell division has been modeled by finite subdivision rules.[4]
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".
Contents |
Variants [edit]
Cells are classified into two categories: simple, non-nucleated prokaryotic cells, and complex, nucleated eukaryotic cells. By dint of 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 ova – egg cells – in females) is different from that of the somatic cell division in the cells of the body.
Degradation [edit]
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, as described in the article on telomere shortening. Cancer cells, on the other hand, are not thought to degrade in this way, if at all. An enzyme called telomerase, present in large quantities in cancerous cells, rebuilds the telomeres, allowing division to continue indefinitely.
See also [edit]
- American Society for Cell Biology
- Binary fission
- Cancer
- Cell growth
- Constantly dividing cells
- Mitosis
Notes [edit]
- ^ Single cell organisms. See discussion within lead of the article on microorganism.
References [edit]
- ^ Ramesh MA, Malik SB, Logsdon JM (January 2005). "A phylogenomic inventory of meiotic genes; evidence for sex in Giardia and an early eukaryotic origin of meiosis". Curr. Biol. 15 (2): 185–91. doi:10.1016/j.cub.2005.01.003. PMID 15668177.
- ^ Maton, Anthea; Hopkins, Jean Johnson, Susan LaHart, David, Quon Warner, David, Wright, Jill D (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.
- ^ J. W. Cannon, W. Floyd and W. Parry. Crystal growth, biological cell growth and geometry. Pattern Formation in Biology, Vision and Dynamics, pp. 65–82. World Scientific, 2000. ISBN 981-02-3792-8,ISBN 978-981-02-3792-9.
- ^ Phase Holographic Imaging. Cell Division
Further reading and reference sources [edit]
- 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
External links [edit]
- How Cells Divide: Mitosis vs. Meiosis
- The Mitosis and Cell Cycle Control Section from the Landmark Papers in Cell Biology (Gall JG, McIntosh JR, eds.) contains commentaries on and links to seminal research papers on mitosis and cell division. Published online in the Image & Video Library of The American Society for Cell Biology
- The Image & Video Library of The American Society for Cell Biology contains many videos showing the cell division.
- Videos of the first cell divisions in Xenopus laevis embryos (side view and top view), acquired by MRI (DOI of paper)
- Images : Calanthe discolor Lindl. - Flavon's Secret Flower Garden
- Tyson's model of cell division and a Description on BioModels Database
- WormWeb.org: Interactive Visualization of the C. elegans Cell Lineage - Visualize the entire set of cell divisions of the nematode C. elegans
|
|||||||||||||||||||||||||||||||
