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Encyclopedia > Endosymbiotic theory

The endosymbiotic theory concerns the origins of mitochondria and plastids (e.g. chloroplasts), which are organelles of eukaryotic cells. According to this theory, these organelles originated as separate prokaryotic organisms which were taken inside the cell as endosymbionts. Mitochondria developed from proteobacteria (in particular, Rickettsiales or close relatives) and chloroplasts from cyanobacteria. Image File history File links Mergefrom. ... It has been suggested that this article or section be merged into Endosymbiotic theory. ... Image File history File links Mergefrom. ... As a logical conclusion of the endosymbiont theory, since modern-day mitochondrial and chloroplast genomes do not contain a full set of housekeeping genes, and lack many that other descendants of their speculative ancestors share, there must have been a loss of genes. ... Electron micrograph of a mitochondrion showing its mitochondrial matrix and membranes In cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed organelle that is found in most eukaryotic cells. ... Plastids are a class of membrane-bound organelles found in plant and algal cells. ... Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. ... Schematic of typical animal cell, showing subcellular components. ... Kingdoms Animalia - Animals Fungi Plantae - Plants Chromalveolata Protista Alternative phylogeny Unikonta Opisthokonta Metazoa Choanozoa Eumycota Amoebozoa Bikonta Apusozoa Cabozoa Rhizaria Excavata Corticata Archaeplastida Chromalveolata Animals, plants, fungi, and protists are eukaryotes (IPA: ), organisms whose cells are organized into complex structures by internal membranes and a cytoskeleton. ... Prokaryotic bacteria cell structure Prokaryotes (IPA: //) are a group of organisms that lack a cell nucleus (= karyon), or any other membrane-bound organelles. ... An endosymbiont is any organism that lives within the body or cells of another organism, i. ... Orders Alpha Proteobacteria    Caulobacterales - e. ... Families Rickettsiaceae Ehrlichiaceae Holosporaceae The Rickettsiales are an order of small proteobacteria. ... Orders The taxonomy is currently under revision. ...

Contents

History

The endosymbiotic theory was first articulated by the Russian botanist Konstantin Mereschkowski in 1905.[1] Mereschkowsky was familiar with work by the German botanist Andreas Schimper, who had observed in 1883 that the division of chloroplasts in green plants closely resembled that of free-living cyanobacteria, and who had himself tentatively proposed (in a footnote) that green plants had arisen from a symbiotic union of two organisms.[2] Ivan Wallin extended the idea of an endosymbiotic origin to mitochondria in the 1920s.[3] These theories were initially dismissed or ignored. More detailed electron microscopic comparisons between cyanobacteria and chloroplasts (for example studies by Hans Ris[4]), combined with the discovery that plastids and mitochondria contain their own DNA[5] (which by that stage was recognized to be the hereditary material of organisms) led to a resurrection of the idea in the 1960s. Konstantin Sergejewicz Mereschkowsky (1855-1921) (Russian: Константин Сергеевич Мережковский, also transliterated Konstantin Sergeevich Merezhkovsky, Konstantin Sergivich Merezhkovsky, Constantin Sergeevič Mérejkovski, Constantin Sergejewicz Mereschcowsky, and Konstantin Sergejewicz Mereschkovsky) was a prominent Russian biologist and botanist active mainly around Kazan, whose research on lichens led him to propose the theory of symbiogenesis - that larger... For other uses, see 1905 (disambiguation). ... Andreas Schimper Andreas Franz Wilhelm Schimper May 12, 1856 Strassburg, Germany - September 9, 1901 Basle, Switzerland was a botanist and phytogeographer who made major contributions in the fields of histology, ecology and plant geography. ... Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. ... Orders The taxonomy is currently under revision. ... Electron micrograph of a mitochondrion showing its mitochondrial matrix and membranes In cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed organelle that is found in most eukaryotic cells. ...


The endosymbiotic hypothesis was fleshed out and popularized by Lynn Margulis. In her 1981 work Symbiosis in Cell Evolution she argued that eukaryotic cells originated as communities of interacting entities, including endosymbiotic spirochaetes that developed into eukaryotic flagella and cilia. This last idea has not received much acceptance, since flagella lack DNA and do not show ultrastructural similarities to prokaryotes. See also Evolution of flagella. Lynn Margulis Dr. Lynn Margulis (born March 15, 1938) is a biologist and University Professor in the Department of Geosciences at the University of Massachusetts Amherst. ... Families Spirochaetaceae Brachyspiraceae    Brachyspira    Serpulina Leptospiraceae    Leptospira    Leptonema Spirochaetes is a phylum of distinctive Gram-negative bacteria, which have long, helically coiled cells. ... For the insect anatomical structure, see Antenna (biology). ... Not to be confused with Psyllium. ... The evolution of flagella is of great interest to biologists because the three known varieties of flagella (eukaryotic, bacterial, and archaebacterial) each represent an extremely sophisticated cellular structure that requires the interaction of many different and finely-tuned systems to function correctly. ...


According to Margulis and Sagan,[6] "Life did not take over the globe by combat, but by networking" (i.e., by cooperation), and Darwin's notion of evolution driven by natural selection is incomplete (see Evolution). This article is about evolution in biology. ...


The possibility that peroxisomes may have an endosymbiotic origin has also been considered, although they lack DNA. Christian de Duve proposed that they may have been the first endosymbionts, allowing cells to withstand growing amounts of free molecular oxygen in the Earth's atmosphere. However, it now appears that they may be formed de novo, contradicting the idea that they have a symbiotic origin (Gabaldón et al. 2006). Basic structure of a peroxisome Peroxisomes are ubiquitous organelles in eukaryotes that participate in the metabolism of fatty acids and other metabolites. ... Christian de Duve (born October 2, 1917) is a biochemist. ...


Evidence

Evidence that mitochondria and plastids arose from ancient endosymbiosis of bacteria is as follows:

  • Both mitochondria and plastids contain DNA that is different from that of the cell nucleus and that is similar to that of bacteria (in being circular and in its size).
  • They are surrounded by two or more membranes, and the innermost of these shows differences in composition from the other membranes of the cell. The composition is like that of a prokaryotic cell membrane.
  • New mitochondria and plastids are formed only through a process similar to binary fission. In some algae, such as Euglena, the plastids can be destroyed by certain chemicals or prolonged absence of light without otherwise affecting the cell. In such a case, the plastids will not regenerate.
  • Much of the internal structure and biochemistry of plastids, for instance the presence of thylakoids and particular chlorophylls, is very similar to that of cyanobacteria. Phylogenetic estimates constructed with bacteria, plastids, and eukaryotic genomes also suggest that plastids are most closely related to cyanobacteria.
  • DNA sequence analysis and phylogenetic estimates suggests that nuclear DNA contains genes that probably came from the plastid.
  • Some proteins encoded in the nucleus are transported to the organelle, and both mitochondria and plastids have small genomes compared to bacteria. This is consistent with an increased dependence on the eukaryotic host after forming an endosymbiosis. Most genes on the organellar genomes have been lost or moved to the nucleus. Most genes needed for mitochondrial and plastid function are located in the nucleus. Many originate from the bacterial endosymbiont.
  • Plastids are present in very different groups of protists, some of which are closely related to forms lacking plastids. This suggests that if chloroplasts originated de novo, they did so multiple times, in which case their close similarity to each other is difficult to explain. Many of these protists contain "secondary" plastids that have been acquired from other plastid-containing eukaryotes, not from cyanobacteria directly.
  • Among the eukaryotes that acquired their plastids directly from bacteria (known as Primoplantae), the glaucophyte algae have chloroplasts that strongly resemble cyanobacteria. In particular, they have a peptidoglycan cell wall between their two membranes.
  • These organelles' ribosomes are like those found in bacteria (70s).
  • Proteins of organelle origin, like those of bacteria, use N-formylmethionine as the initiating amino acid.

The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ... A biological membrane or biomembrane is an enclosing or separating tissue which acts as a barrier within or around a cell. ... Binary fission Binary fission is the form of asexual reproduction in single-celled organisms by which one cell divides into two cells of the same size, used by most prokaryotes. ... A seaweed (Laurencia) up close: the branches are multicellular and only about 1 mm thick. ... Hey Euglena is a common Euglenophyte protist, typical of the euglenids, and commonly found in nutrient-rich freshwater, with a few marine species. ... Thylakoids (green) inside a chloroplast Thylakoids (green) inside a cyanobacterium (Synechocystis) A Thylakoid is a membrane-bound compartment inside chloroplasts and cyanobacteria. ... Chlorophyll is a green pigment found in most plants, algae, and cyanobacteria. ... Orders The taxonomy is currently under revision. ... In biology, phylogenetics (Greek: phylon = tribe, race and genetikos = relative to birth, from genesis = birth) is the study of evolutionary relatedness among various groups of organisms (e. ... In biology, phylogenetics (Greek: phylon = tribe, race and genetikos = relative to birth, from genesis = birth) is the study of evolutionary relatedness among various groups of organisms (e. ... Typical phyla Chromalveolata Chromista Heterokontophyta Haptophyta Cryptophyta (cryptomonads) Alveolata Dinoflagellata Apicomplexa Ciliophora (ciliates) Cabozoa Excavata Euglenozoa Percolozoa Metamonada Rhizaria Radiolaria Foraminifera Cercozoa Archaeplastida (in part) Rhodophyta (red algae) Glaucophyta (basal archaeplastids) Amoebozoa Choanozoa Many others; classification varies Protists (IPA: (RP); (GenAm)), Greek protiston -a meaning the (most) first of all... subgroups Glaucophyta Rhodophyta (Red algae) Viridiplantae (green plants) (= Chlorobionta) Green algae (grade group) Embryophyta (Land plants) Primoplantae is a group of organisms that includes green plants (green algae and land plants), red algae, and an obscure group of single-celled algae called the glaucophytes. ... The glaucophytes, also referred to as glaucocystophytes or glaucocystids, are a tiny group of freshwater algae. ... Peptidoglycan, also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of eubacteria. ... Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ...

Secondary Endosymbiosis

Primary endosymbiosis involves the engulfment of a bacterium by another free living organism. Secondary endosymbiosis occurs when the product of primary endosymbiosis is itself engulfed and retained by another free living eukaryote. Secondary endosymbiosis has occurred several times and has given rise to extremely diverse groups of algae and other eukaryotes. Some organisms can take opportunistic advantage of a similar process, where they engulf an alga and use the products of its photosynthesis, but once the prey item dies (or is lost) the host returns to a free living state. Obligate secondary endosymbionts become dependent on their organelles and are unable to survive in their absence (for a review see McFadden 2001[7]).


One possible secondary endosymbiosis in process has been observed by Okamoto & Inouye (2005). The heterotrophic protist Hatena behaves like a predator until it ingests a green algae, which loses its flagella and cytoskeleton, while Hatena, now a host, switches to photosynthetic nutrition, gains the ability to move towards light and loses its feeding apparatus. Hatena (or mysterious) is a new creature discovered in Japan. ... Divisions Chlorophyta Charophyta Green algae are microscopic protists; found in all aquatic environments, including marine, freshwater and brackish water. ...


Problems

  • Neither mitochondria nor plastids can survive in oxygen or outside the cell, having lost many essential genes required for survival. This objection is easily accounted for by simply considering the large timespan that the mitochondria/plastids have co-existed with their hosts; genes and systems which were no longer necessary were simply deleted, or in many cases, transferred into the host genome instead. (In fact these transfers constitute an important way for the host cell to regulate plastid or mitochondrial activity.)

See also

The evolution of flagella is of great interest to biologists because the three known varieties of flagella (eukaryotic, bacterial, and archaebacterial) each represent an extremely sophisticated cellular structure that requires the interaction of many different and finely-tuned systems to function correctly. ... A flagellum (plural, flagella) is a whip-like organelle that many unicellular organisms, and some multicellular ones, use to move about. ... Hatena (or mysterious) is a new creature discovered in Japan. ... The Hydrogen hypothesis is a model that describes how the first eukaryotic cell may have developed. ... For other uses, see Lichen (disambiguation). ... Symbiogenesis refers to the merging of two separate organisms to form a single new organism. ... As a logical conclusion of the endosymbiont theory, since modern-day mitochondrial and chloroplast genomes do not contain a full set of housekeeping genes, and lack many that other descendants of their speculative ancestors share, there must have been a loss of genes. ... This article or section is in need of attention from an expert on the subject. ... A protobiont is an aggregate of abiotically produced organic molecules, that has been demonstrated to be formed by self assembly. ... Numt (pronounced “new might”) is an abbreviated term for “nuclear mitochondrial DNA”, which describes any transfer or “transposition” of cytoplasmic mitochondrial DNA sequences into the separate nuclear genome of a eukaryotic organism. ...

Notes

  1. ^ Mereschkowski C (1905). "Über Natur und Ursprung der Chromatophoren im Pflanzenreiche". Biol Centralbl 25: 593-604. 
  2. ^ Schimper AFW (1883). "Über die Entwicklung der Chlorophyllkörner und Farbkörper". Bot. Zeitung 41: 105-14, 121-31, 137-46, 153-62. 
  3. ^ Wallin IE (1923). "The Mitochondria Problem". The American Naturalist 57:650: 255-261. 
  4. ^ Ris H and Singh RN (1961). "Electron microscope studies on blue-green algae". J Biophys Biochem Cytol 9: 63-80. 
  5. ^ Stocking C and Gifford E (1959). "Incorporation of thymidine into chloroplasts of Spirogyra". Biochem. Biophys. Res. Comm. 1: 159-64. 
  6. ^ Margulis, Lynn and Sagan (2001). "Marvellous microbes". Resurgence 206: 10–12. 
  7. ^ McFadden GI (2001). "Primary and secondary endosymbiosis and the origin of plastids". J Phycology 37 (6): 951-959. 

References

  • Bruce Alberts, Dr. Manigga Suckmeoff, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts and Peter Walter, Molecular Biology of the Cell, Garland Science, New York, 2002. ISBN 0-8153-3218-1. (General textbook)
  • Jeffrey L. Blanchard and Michael Lynch (2000), "Organellar genes: why do they end up in the nucleus?", Trends in Genetics, 16 (7), pp. 315-320. (Discusses theories on how mitochondria and chloroplast genes are transferred into the nucleus, and also what steps a gene needs to go through in order to complete this process.) [1]
  • Paul Jarvis (2001), "Intracellular signalling: The chloroplast talks!", Current Biology, 11 (8), pp. R307-R310. (Recounts evidence that chloroplast-encoded proteins affect transcription of nuclear genes, as opposed to the more well-documented cases of nuclear-encoded proteins that affect mitochondria or chloroplasts.) [2]
  • Fiona S.L. Brinkman, Jeffrey L. Blanchard, Artem Cherkasov, Yossef Av-Gay, Robert C. Brunham, Rachel C. Fernandez, B. Brett Finlay, Sarah P. Otto, B.F. Francis Ouellette, Patrick J. Keeling, Ann M. Rose, Robert E.W. Hancock, and Steven J.M. Jones (2002,) Evidence That Plant-Like Genes in Chlamydia Species Reflect an Ancestral Relationship between Chlamydiaceae, Cyanobacteria, and the Chloroplast Genome Res., 12: pp 1159 - 1167. [3]
  • Okamoto, N. & Inouye, I. (2005), "A Secondary Symbiosis in Progress?", Science, 310, p. 287
  • Guenther Witzany (2006), "Serial Endosymbiotic Theory (SET): The Biosemiotic Update", Acta Biotheoretica, 54(1), pp. 103-117
  • Gabaldón T. et al (2006), "Origin and evolution of the peroxisomal proteome", Biology Direct, 1 (8),. (Provides evidence that contradicts an endosymbiotic origin of peroxisomes. Instead it is suggested that they evolutionarily originate from the Endoplasmic Reticulum) [4]
Fiona Brinkman (nee Lawson) is an Associate Professor in Bioinformatics and Genomics (Department of Molecular Biology and Biochemistry[1]) at Simon Fraser University, British Columbia, Canada, and is a leader in the area of pathogen bioinformatics. ...

  Results from FactBites:
 
Endosymbiotic theory - Biocrawler (0 words)
The endosymbiotic theory concerns the origins of mitochondria and chloroplasts, which are organelles of eukaryotic cells.
According to this theory, these originated as prokaryotic organisms, which came to live inside eukaryotic cells as endosymbionts.
The theory postulates that the mitochondria evolved from aerobic bacteria (probably proteobacteria, related to the rickettsias), and that the chloroplast evolved from endosymbiotic cyanobacteria (autotrophic prokaryotes).
  More results at FactBites »

 
 

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