Fission (biology)

Fission, in biology, is the division of a single entity into two or more parts and the regeneration of those parts into separate entities resembling the original. The object experiencing fission is usually a cell, but the term may also refer to how organisms, bodies, populations, or species split into discrete parts.[1][2][3] The fission may be binary fission, in which a single entity produces two parts, or multiple fission, in which a single entity produces multiple parts.

Binary fission

Bacilli division diagram
Schematic diagram of cellular growth (elongation) and binary fission of bacilli. Blue and red lines indicate old and newly generated bacterial cell wall, respectively. (1) growth at the centre of the bacterial body. e.g. Bacillus subtilis, E. coli, and others. (2) apical growth. e.g. Corynebacterium diphtheriae.

Organisms in the domains of Archaea and Bacteria reproduce with binary fission. This form of asexual reproduction and cell division is also used by some organelles within eukaryotic organisms (e.g., mitochondria). Binary fission results in the reproduction of a living prokaryotic cell (or organelle) by dividing the cell into two parts, each with the potential to grow to the size of the original.

Fission of prokaryotes

The single DNA molecule first replicates, then attaches each copy to a different part of the cell membrane. When the cell begins to pull apart, the replicated and original chromosomes are separated. The consequence of this asexual method of reproduction is that all the cells are genetically identical, meaning that they have the same genetic material (barring random mutations). Unlike the process of mitosis used by eukaryotic cells, binary fission takes place without the formation of a spindle apparatus on the cell. In binary fission the parental identity is lost.

Process of bacterial fission

Binary Fission 2
Binary fission in a prokaryote

The process of binary fission in bacteria involves the following steps. First, the cell's DNA is replicated. The replicated DNA copies then move to opposite poles of the cell in an energy-dependent process.[4] The cell lengthens. Then, the equatorial plane of the cell constricts and separates the plasma membrane such that each new cell has exactly the same genetic material.

More specifically, the following steps occur:

  1. The bacterium before binary fission is when the DNA is tightly coiled.
  2. The DNA of the bacterium has uncoiled and duplicated.
  3. The DNA is pulled to the separate poles of the bacterium as it increases the size to prepare for splitting.
  4. The growth of a new cell wall begins to separate the bacterium.
  5. The new cell wall fully develops, resulting in the complete split of the bacterium.
  6. The new daughter cells have tightly coiled DNA rods, ribosomes, and plasmids; these are now brand new organisms.

Speed of bacterial fission

Binary fission is generally rapid though its speed varies between species. For E. coli, cells typically divide about every 20 minutes at 37 °C.[5] Because the new cells will, in turn, undergo binary fission on their own, the time binary fission requires is also the time the bacterial culture requires to double in the number of cells it contains. This time period can, therefore, be referred to as the doubling time. Some species other than E. coli may have faster or slower doubling times: some strains of Mycobacterium tuberculosis may have doubling times of nearly 100 hours.[6] Bacterial growth is limited by factors including nutrient availability and available space, so binary fission occurs at much lower rates in bacterial cultures once they enter the stationary phase of growth.

Fission of organelles

Some organelles in eukaryotic cells reproduce using binary fission. Mitochondrial fission occurs frequently within the cell, even when the cell is not actively undergoing mitosis, and is necessary to regulate the cell's metabolism.[7]

Types of binary fission

Binary fission in organisms can occur in four ways, irregular,longitudinal, transverse, oblique.

  1. Irregular: In this fission, cytokinesis may take place along any plane but it is always perpendicular to the plane of karyokinesis. e.g. amoeba
  2. Longitudinal: Here cytokinesis takes place along the longitudinal axis. e.g. in flagellates like Euglena.
  3. Transverse: Here cytokinesis takes place along the transverse axis. e.g. in ciliate protzoans like paramecium.
  4. Oblique: In this type of binary fission cytokinesis occurs obliquely. e.g. ceratium

Multiple fission

Fission of protists

Multiple fission at the cellular level occurs in many protists, e.g. sporozoans and algae. The nucleus of the parent cell divides several times by amitosis, producing several nuclei. The cytoplasm then separates, creating multiple daughter cells.[8][9][10]

Some parasitic, single-celled organisms undergo a multiple fission-like process to produce numerous daughter cells from a single parent cell. Isolates of the human parasite Blastocystis hominis were observed to begin such a process within 4 to 6 days.[11] Cells of the fish parasite Trypanoplasma borreli have also been observed participating in both binary and multiple fission.[12]

Fission of apicomplexans

In the apicomplexans, a phylum of parasitic protists, multiple fission, or schizogony, is manifested either as merogony, sporogony or gametogony. Merogony results in merozoites, which are multiple daughter cells, that originate within the same cell membrane,[13][14] sporogony results in sporozoites, and gametogony results in microgametes.

Fission of green algae

Green algae can divide into more than two daughter cells. The exact number of daughter cells depends on the species of algae and is an effect of temperature and light.[15]

Multiple fission of bacteria

Most species of bacteria primarily undergo binary reproduction. Some species and groups of bacteria may undergo multiple fission as well, sometimes beginning or ending with the production of spores.[16] The species Metabacterium polyspora, a symbiont of guinea pigs, has been found to produce multiple endospores in each division.[17] Some species of cyanobacteria have also been found to reproduce through multiple fission.[18]

Plasmotomy

Some protozoans reproduce by yet another mechanism of fission called as plasmotomy. In this type of fission, a multinucleate adult parent undergoes cytokinesis to form two multinucleate (or coenocytic) daughter cells. The daughter cells so produced undergo karyokinesis, further.

Such a type of reproduction is shown by opalina and pelomyxa.

Clonal fragmentation

Fragmentation in multicellular or colonial organisms is a form of asexual reproduction or cloning where an organism is split into fragments. Each of these fragments develop into mature, fully grown individuals that are clones of the original organism. In echinoderms, this method of reproduction is usually known as fissiparity.[19]

Population fission

Any splitting of a single population of individuals into discrete parts may be considered fission. A population may undergo fission for a variety of reasons, including migration or geographic isolation. Because the fission leads to genetic variance in the newly isolated, smaller populations, population fission is a precursor to speciation.[20][21]

See also

References

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  3. ^ Hubbell, S. (2003). "Modes of speciation and the lifespans of species under neutrality: a response to the comment of Robert E. Ricklefs". Oikos. 100 (1): 193–199. doi:10.1034/j.1600-0706.2003.12450.x.
  4. ^ Rokney, Assaf; Shagan, Merav; Kessel, Martin; Smith, Yoav; Rosenshine, Ilan; Oppenheim, Amos B. (September 2009). "E. coli Transports Aggregated Proteins to the Poles by a Specific and Energy-Dependent Process". Journal of Molecular Biology. 392 (3): 589–601. doi:10.1016/j.jmb.2009.07.009. PMID 19596340.
  5. ^ Sezonov, G.; Joseleau-Petit, D.; D'Ari, R. (28 September 2007). "Escherichia coli (E coli) Physiology in Luria-Bertani Broth". Journal of Bacteriology. 189 (23): 8746–8749. doi:10.1128/JB.01368-07. PMC 2168924.
  6. ^ North, R. J. (1 June 1993). "Mycobacterial virulence. Virulent strains of Mycobacteria tuberculosis have faster in vivo doubling times and are better equipped to resist growth-inhibiting functions of macrophages in the presence and absence of specific immunity". Journal of Experimental Medicine. 177 (6): 1723–1733. doi:10.1084/jem.177.6.1723.
  7. ^ van der Bliek, A. M.; Shen, Q.; Kawajiri, S. (3 June 2013). "Mechanisms of Mitochondrial Fission and Fusion". Cold Spring Harbor Perspectives in Biology. 5 (6): a011072–a011072. doi:10.1101/cshperspect.a011072. PMC 3660830.
  8. ^ "Cell reproduction". Encyclopædia Britannica.
  9. ^ Britannica Educational Publishing (2011). Fungi, Algae, and Protists. The Rosen Publishing Group. ISBN 978-1-61530-463-9. Retrieved 2016-12-21.
  10. ^ P.Puranik, Asha Bhate (2007). Animal Forms And Functions: Invertebrata. Sarup & Sons. ISBN 978-81-7625-791-6. Retrieved 2016-12-21.
  11. ^ Suresh, K.; Howe, J.; Ng, G. C.; Ho, L. C.; Ramachandran, N. P.; Loh, A. K.; Yap, E. H.; Singh, M. (1994). "A multiple fission-like mode of asexual reproduction inBlastocystis hominis". Parasitology Research. 80 (6): 523–527. doi:10.1007/BF00932701.
  12. ^ Pecková, H.; Lom, J. (1990). "Growth, morphology and division of flagellates of the genusTrypanoplasma (Protozoa, Kinetoplastida) in vitro". Parasitology Research. 76 (7): 553–558. doi:10.1007/BF00932559.
  13. ^ Lynn Margulis; Heather I. McKhann; Lorraine Olendzenski (1993). Illustrated glossary of protoctista: vocabulary of the algae, apicomplexa, ciliates, foraminifera, microspora, water molds, slime molds, and the other protoctists. Jones & Bartlett Learning. ISBN 978-0-86720-081-2. Retrieved 2016-12-21.
  14. ^ Yoshinori Tanada; Harry K. Kaya (1993). Insect pathology. Gulf Professional Publishing. ISBN 978-0-12-683255-6. Retrieved 2016-12-21.
  15. ^ Bišová, K.; Zachleder, V. (17 January 2014). "Cell-cycle regulation in green algae dividing by multiple fission" (PDF). Journal of Experimental Botany. 65 (10): 2585–2602. doi:10.1093/jxb/ert466. PMID 24441762. Retrieved 23 August 2016.
  16. ^ Angert, Esther R. (March 2005). "Alternatives to binary fission in bacteria" (PDF). Nature Reviews Microbiology. 3 (3): 214–224. doi:10.1038/nrmicro1096. PMID 15738949. Retrieved 23 August 2016.
  17. ^ Angert, E. R.; Losick, R. M. (18 August 1998). "Propagation by sporulation in the guinea pig symbiont Metabacterium polyspora". Proceedings of the National Academy of Sciences. 95 (17): 10218–10223. doi:10.1073/pnas.95.17.10218.
  18. ^ Stanier, Roger Y.; Deruelles, Josette; Rippka, Rosmarie; Herdman, Michael; Waterbury, John B. (1 March 1979). "Generic Assignments, Strain Histories and Properties of Pure Cultures of Cyanobacteria". Microbiology. 111 (1): 1–61. doi:10.1099/00221287-111-1-1.
  19. ^ Helen Nilsson Sköld; Matthias Obst; Mattias Sköld; Bertil Åkesson (2009). "Stem Cells in Asexual Reproduction of Marine Invertebrates". In Baruch Rinkevich; Valeria Matranga. Stem Cells in Marine Organisms. Springer. p. 125. ISBN 978-90-481-2766-5. Retrieved 2016-12-21.
  20. ^ Whitlock, Michael C. (May 1994). "Fission and the Genetic Variance Among Populations: The Changing Demorgraphy of Forked Fungus Beetle Populations". The American Naturalist. 143 (5): 820–829. doi:10.1086/285634. JSTOR 2462878.
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Budding

Budding is a type of asexual reproduction in which a new organism develops from an outgrowth or bud due to cell division at one particular site. The small bulb like projection coming out from the yeast cell is called a bud. The new organism remains attached as it grows, separating from the parent organism only when it is mature, leaving behind scar tissue. Since the reproduction is asexual, the newly created organism is a clone and is genetically identical to the parent organism.

Organisms such as hydra use regenerative cells for reproduction in the process of budding.

In hydra, a bud develops as an outgrowth due to repeated cell division at one specific site. These buds develop into tiny individuals and, when fully mature, detach from the parent body and become new independent individuals.

Internal budding or endodyogeny is a process of asexual reproduction, favoured by parasites such as Toxoplasma gondii. It involves an unusual process in which two daughter cells are produced inside a mother cell, which is then consumed by the offspring prior to their separation.Endopolygeny is the division into several organisms at once by internal budding.

Divisome

The divisome is a protein complex in bacteria that is responsible for cell division, constriction of inner and outer membranes during division, and peptidoglycan (PG) synthesis at the division site. The divisome is a membrane protein complex with proteins on both sides of the cytoplasmic membrane. In gram-negative cells it is located in the inner membrane. The divisome is nearly ubiquitous in bacteria although its composition may vary between species.The elongasome is a modified version of the divisome, without the membrane-constricting FtsZ-ring and its associated machinery. The elongasome is present only in non-spherical bacteria and directs lateral insertion of PG along the long axis of the cell, thus allowing cylindrical growth (as opposed to spherical growth, as in cocci).

Fragmentation (reproduction)

Fragmentation in multicellular organisms is a form of asexual reproduction in which an organism is split into fragments. Each of these fragments develop into matured, fully grown individuals that are identical to their parents

The splitting may or may not be intentional – it may or may not occur due to man-made or natural damage by the environment or predators. This kind of organism may develop specific organs or zones that may be shed or easily broken off. If the splitting occurs without the prior preparation of the organism, both fragments must be able to regenerate the complete organism for it to function as reproduction.

Fragmentation, also known as splitting, as a method of reproduction is seen in many organisms such as filamentous cyanobacteria, molds, lichens, many plants, and animals such as sponges, acoel flatworms, some annelid worms and sea stars.

FtsZ

FtsZ is a protein encoded by the ftsZ gene that assembles into a ring at the future site of the septum of bacterial cell division. This is a prokaryotic homologue to the eukaryotic protein tubulin. FtsZ has been named after "Filamenting temperature-sensitive mutant Z". The hypothesis was that cell division mutants of E. coli would grow as filaments due to the inability of the daughter cells to separate from one another.

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