“Cell division”的意思、由来-开放百科全书

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: a vegetative division, whereby each daughter cell is genetically identical to the parent cell (mitosis),^[2] 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 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) 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 microorganisms 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.^[3] The human body experiences about 10 quadrillion cell divisions in a lifetime.^[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.^[5] A great deal of cellular infrastructure is involved in keeping genomic information consistent between generations.

Phases of cell division

Interphase

Interphase is the process a cell must go through before mitosis, meiosis, and cytokinesis.^[6] 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 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, 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. 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. There are three transition checkpoints the cell goes through before entering the M phase. The most important being the G1-S transition checkpoint. If the cell does not pass this phase, then the cell will most likely not go through the rest of the cell division cycle.

Prophase

Prophase is the first stage of division. The nuclear envelope is broken down, long strands of chromatin condense to form shorter more visible strands called chromosomes, the nucleolus disappears, and microtubules attach to the chromosomes at the kinetochores present in the centromere.^[7] 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, homologous [chromosomes cross] over.

Metaphase

In metaphase, the centromeres of the chromosomes convene themselves on the metaphase plate (or equatorial plate), an imaginary line that is equidistant from the two centrosome poles. 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.^[8] Spindle fibres 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

Telophase

Variants

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.

Degradation

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.{{citation needed|date=October 2016}} 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.

History

A cell division under microscope was first discovered by German botanist Hugo von Mohl in 1835 as he worked over Green algae Cladophora glomerata.^[15]

In 1943, cell division was filmed for the first time^[16] by Kurt Michel using a phase-contrast microscope.^[17]

See also

References

1. ^{{cite book|title=Oxford Dictionary Biology|year=2008|publisher=Oxford University Press|location=New York|isbn=978-0-19-920462-5|edition=6th|editor=Robert.S Hine|page=113}}
2. ^{{cite book|last=Griffiths|first=Anthony J.F.|title=Introduction to Genetic Analysis|year=2012|publisher=W.H. Freeman and Company|location=New York|isbn=978-1-4292-2943-2|page=35|edition=10|author2=Wessler, Susan R.|author3=Carroll, Sean B.|author4=Doebley, John}}
3. ^{{cite book | last = Maton | first = Anthea | title = Cells: Building Blocks of Life | publisher = Prentice Hall | year = 1997 | location = New Jersey | pages = 70–74 | url = | doi = | id = | isbn = 978-0-13-423476-2 }}
4. ^{{Cite journal | last = Quammen | first = David | authorlink = David Quammen | title = Contagious cancer: The evolution of a killer | url = http://harpers.org/archive/2008/04/0081988 | journal = Harper's | volume = 316 | issue = 1895 | page = 42 | date = April 2008 | accessdate = 24 September 2012}}
5. ^{{Cite book|title=Cell Division: Theory, Variants, and Degradation|last=Krylov|first=Mikhail C.|publisher=Nova Science Publishers, Inc.|year=2010|isbn=9781608769865|location=New York|pages=137}}
6. ^{{Cite book|title=Essentials of human anatomy and physiology|last=Marieb|first=Elaine|publisher=Benjamin Cummings|year=2000|isbn=978-0-8053-4940-5|location=San Francisco|pages=|quote=|via=}}
7. ^{{Cite journal |last=Schermelleh |first=Lothar |last2=Carlton |first2=Peter M. |last3=Haase |first3=Sebastian |last4=Shao |first4=Lin |last5=Winoto |first5=Lukman |last6=Kner |first6=Peter |last7=Burke |first7=Brian |last8=Cardoso |first8=M. Cristin |last9=Agard |first9=David A. |date=2008-06-06 |title=Subdiffraction Multicolor Imaging of the Nuclear Periphery with 3D Structured Illumination Microscopy |journal=Science |volume=320 |issue=5881 |pages=1332–1336 |doi=10.1126/science.1156947 |issn=0036-8075 |pmc=2916659 |pmid=18535242}}
8. ^{{cite web |url=https://www.sciencedaily.com/releases/2007/06/070611122252.htm |title=Researchers Shed Light On Shrinking Of Chromosomes |date=June 12, 2007 |website=ScienceDaily |access-date=2017-02-02}}
9. ^{{cite book|last1=Elrod|first1=Susan|title=Schaum's Outline of Genetics|date=2002|publisher=McGraw-Hill Companies, Inc|location=United States of America|isbn=9780071625036|page=8|edition=Fifth}}
10. ^{{Cite web|url=http://www.biology-pages.info/C/CellCycle.html|title=The Cell Cycle|website=www.biology-pages.info|access-date=2017-02-02}}
11. ^{{Cite journal|date=September 2013|title=Campbell Biology in Focus. By Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson, and Jane B. Reece. Boston (Massachusetts): Pearson. $146.67. xxxix + 905 p.; ill. + A-1 - A-34; B-1; C-1; D-1; E-1 - E-2; F-1 - F-3; CR-1 - CR-6; G-1 - G-34; I-1 - I-48 (index). ISBN: 978-0-321-81380-0. 2014.|journal=The Quarterly Review of Biology|volume=88|issue=3|pages=242|doi=10.1086/671541|issn=0033-5770}}
12. ^{{Cite journal|last=Dekker|first=Job|date=2014|title=Two ways to fold the genome during the cell cycle: insights obtained with chromosome conformation capture|journal=Epigenetics & Chromatin|volume=7|issue=1|pages=25|doi=10.1186/1756-8935-7-25|pmid=25435919|issn=1756-8935}}
13. ^{{Cite journal|last=Hetzer|first=Martin W.|date=2017-02-02|title=The Nuclear Envelope|journal=Cold Spring Harbor Perspectives in Biology|volume=2|issue=3|pages=a000539|doi=10.1101/cshperspect.a000539|issn=1943-0264|pmc=2829960|pmid=20300205}}
14. ^[https://web.archive.org/web/20130629210808/http://www.phiab.se/applications/cell-division Phase Holographic Imaging. Cell Division]
15. ^{{NDB|17|690|691|Mohl, Hugo von|Karl Mägdefrau|118830538}}
16. ^{{Cite book|title=eLS (formerly Encyclopedia of Life Sciences)|last=Masters|first=Barry R|date=2008|publisher=John Wiley & Sons, Ltd|isbn=9780470015902|location=|pages=3|language=en|chapter=History of the Optical Microscope in Cell Biology and Medicine|doi=10.1002/9780470015902.a0003082|chapter-url=http://www.fen.bilkent.edu.tr/~physics/news/masters/ELS_LM.pdf}}
17. ^{{YouTube|Ge4k3uiB3qw}}