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Line 2: + + + + − == History ==+ − − The endosymbiotic theory was first articulated by famed [[Russian]] botanist Konstantin Mereschkowski in 1905<ref>Mereschkowski C (1905). "Über Natur und Ursprung der Chromatophoren im Pflanzenreiche". Biol Centralbl 25: 593–604.</ref>. Mereschkowski based his theory in part on work done by botanist Andreas Schimper, who had observed in 1883 that the division of chloroplasts in green [[plants]] closely resembled that of cyanobacteria. Schimper had himself tentatively proposed (in a footnote) that green plants could have arisen from the symbiosis of two simpler organisms.<ref>Schimper AFW (1883). "Über die Entwicklung der Chlorophyllkörner und Farbkörper". Bot. Zeitung 41: 105–14, 121–31, 137–46, 153–62.</ref> In the 1920s, Irvin Wallin, a [[professor]] at the University of Colorado Medical School, extended the idea of an endosymbiotic origin to the mitochondria.<ref>Wallin IE (1923). "The Mitochondria Problem". The American Naturalist 57 (650): 255–61. doi:10.1086/279919. − </ref> These theories were initially dismissed (or ignored) by the scientific community. More detailed electron microscopic comparisons between cyanobacteria and chloroplasts (for example, studies by Hans Ris<ref>Ris H, Singh RN (January 1961). "Electron microscope studies on blue-green algae". J Biophys Biochem Cytol 9 (1): 63–80. doi:10.1083/jcb.9.1.63. PMC 2224983. PMID 13741827.</ref>) combined with the discovery that plastids and mitochondria contain their own [[DNA]]<ref>Stocking C and Gifford E (1959). "Incorporation of thymidine into chloroplasts of Spirogyra". Biochem. Biophys. Res. Comm. 1 (3): 159–64. doi:10.1016/0006-291X(59)90010-5. − </ref> (which had recently been identified as the hereditary material of organisms) led to a resurrection of the idea in the 1960s. − The endosymbiotic theory was advanced and substantiated with [[microbiology|microbiological]] evidence in 1967 by [[American]] biologist Lynn Margulis. A young faculty member at [[Boston University]], Margulis authored a theoretical paper entitled ''The Origin of Mitosing Eukaryotic Cells''<ref>Lynn Sagan (1967). "On the origin of mitosing cells". J Theor Bio. 14 (3): 255–274. doi:10.1016/0022-5193(67)90079-3. PMID 11541392.</ref>. The paper, however, was "rejected by about fifteen scientific journals," Margulis recalled<ref>John Brockman, The Third Culture, New York: Touchstone, 1995, 135.</ref>(see [[Best of the Public]]). It was finally accepted by ''The Journal of Theoretical Biology'' and is considered today a landmark in modern endosymbiotic theory. Drawing heavily from the ideas of Mereschkowski and Wallin, Margulis's endosymbiotic theory formulation is the first to rely on direct microbiological observations as opposed to [[paleontology|paleontological]] or [[zoology|zoological]] observations, which were previously the norm for new works in [[evolutionary biology]]. + − + − == Evidence ==+ − A great body of evidence exists in the fields of [[molecular biology]], [[biochemistry]], and [[genetics]] that supports the theory that mitochondria and plastids arose from bacteria<ref>Kimball, J. 2010. Kimball's Biology Pages. Accessed October 13, 2010. An online open source biology text by Harvard professor, and author of a general biology text, John W. Kimball.</ref><ref>Reece, J., Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson, 2010. Campbell Biology. 9th Edition Benjamin Cummings; 9th Ed. (October 7, 2010)</ref><ref>Raven, P., George Johnson, Kenneth Mason, Jonathan Losos, Susan Singer, 2010. Biology. McGraw-Hill 9th Ed. (January 14, 2010)</ref>.+ − * 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. − * They are surrounded by two or more membranes, and the innermost of these shows differences in composition from the other membranes of the cell. They are composed of a peptidoglycan [[cell wall]] characteristic of a bacterial cell. − * 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 in shape and in its size). − * DNA sequence analysis and [[phylogeny|phylogenetic]] estimates suggest that nuclear DNA contains genes that probably came from plastids. − * 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. − *Much of the internal structure and biochemistry of plastids, for instance the presence of thylakoids and particular [[chlorophyll|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. − * Mitochondria have several [[enzyme|enzymes]] and transport systems similar to those of bacteria. − * 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 "primary" plastids that have not yet been acquired from other plastid-containing eukaryotes. − * Among 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 the two membranes. − * Mitochondria and plastids are similar in size to bacteria. Line 37:
Line 24: + − == Serial Endosymbiosis Theory and Evolution ==+ + + − + − <blockquote>+ − I greatly admire Lynn Margulis's sheer courage and stamina in sticking by the endosymbiosis theory, and carrying it through from being an unorthodoxy to an orthodoxy. I'm referring to the theory that the eukaryotic cell is a symbiotic union of primitive prokaryotic cells. This is one of the great achievements of twentieth-century evolutionary biology, and I greatly admire her for it.<ref>John Brockman, The Third Culture, New York: Touchstone, 1995, 144.</ref> − </blockquote> − − There are essentially two differing views concerning endosymbiotic theory, one slightly more logical than the other: − * [[Creationists]] (rightfully) assume that [[God]], in His infinite wisdom, designed a complex cellular system that allows modern organisms to function perfectly on a ''molecular level''. Endosymbiotic theory speaks to the majesty of His [[creation]]. Indeed, when confronted with endosymbiotic theory, [[Christians]] often think of the words of Daniel: "I will praise thee, for I am fearfully and wonderfully made." − * The general consensus of the scientific community is that endosymbiotic theory is a demonstrated fact, backed up by a mountain of molecular/biochemical evidence. This fact, in conjunction with a wealth of biological research, confirms Darwin's theory of evolution as a scientific truth. + + + − * [[Biology]]
Reverted edits by XavierC (talk) to last revision by Conservative
the origins of [[mitochondria]], plastids (e.g. [[chloroplasts]]), and [[nuclei]] in [[eukaryotes|eukaryotic cells]]. According
the origins of [[mitochondria]], plastids (e.g. [[chloroplasts]]), and [[nuclei]] in [[eukaryotes|eukaryotic cells]]. According
to this theory, these organelles arose from free-living bacteria that were taken inside another cell as endosymbionts.
to this theory, these organelles arose from free-living bacteria that were taken inside another cell as endosymbionts.
== Creation science critique of the edosymbiotic hypothesis ==
[[Image:Carl weiland.jpg|thumbnail|150px|right|Dr. [[Carl Wieland]] is the Managing Director of Creation Ministries International ]]
Citing a biology textbook [[Creation Ministries International]] writes:
{{cquote|Sometimes it is stated more cautiously:
‘In the endosymbiont theory, the ancestor of the eukaryotic cell (we will call this organism a protoeukaryote) is presumed to have been a large, anaerobic, heterotrophic prokaryote that obtained its energy by a glycolytic pathway. Unlike present-day bacteria, this organism had the ability to take up particulate matter … . '''The endosymbiont theory''' postulates that a condition arose in which a large, particularly complex, anaerobic prokaryote took up a small aerobic prokaryote into its cytoplasm and retained it in a permanent state [emphasis added].’
Whichever way it is stated, it is given an aura of authority and certainty by its frequent repetition in writings on cell biology. Many students find it convincing. However, like many [[evolution|evolutionary]] ideas, it may look solid from a distance, but gaps appear on close scrutiny.
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|Earth's]] atmosphere. However, it now appears that they may be formed ''de novo'', contradicting the idea that they have a symbiotic origin<ref>Gabaldón T, Snel B, van Zimmeren F, Hemrika W, Tabak H, Huynen MA (2006). "Origin and evolution of the peroxisomal proteome". Biol. Direct 1 (1): 8. doi:10.1186/1745-6150-1-8. PMC 1472686. PMID 16556314. (Provides evidence that contradicts an endosymbiotic origin of peroxisomes. Instead it is suggested that they evolutionarily originate from the Endoplasmic Reticulum)</ref>. It is believed that over millennia these endosymbionts transferred some of their own DNA to the host cell's nucleus during the evolutionary transition from a symbiotic community to an instituted eukaryotic cell (called "serial endosymbiosis"). This hypothesis is thought to be possible because it is known today from scientific observation that transfer of DNA occurs between [[bacteria]] species, even if they are not closely related. Bacteria can take up DNA from their surroundings and have a limited ability to incorporate it into their own [[genome]].
The evidence for the endosymbiont theory revolves around selected similarities between mitochondria and bacteria, especially the DNA ring structure. However, these similarities do not prove evolutionary relationship. There is no clear pathway from any one kind of bacteria to mitochondria, although several types of bacteria share isolated points of similarity. Indeed, the scattered nature of these similarities has left plenty of room for a less-publicized ‘direct evolution’ theory of mitochondrial origin, in which they never had any free-living stage. There is enough diversity among the mitochondria of protozoa to make evolutionists wonder if endosymbiotic origin of mitochondria occurred more than once.
Mitochondrial DNA
The endosymbiont theory implies that there should be considerable autonomy for mitochondria. This is not the case. Mitochondria are far from self-sufficient even in their DNA, which is their most autonomous feature. Mitochondria actually have most of their proteins coded by nuclear genes, including their DNA synthesis enzymes.<ref>http://creation.com/mitochondria-created-to-energize-us</ref>}}
== Problems ==
== Problems ==
These last two problems are accounted for by the [http://www.fbmc.fcen.uba.ar/materias/genmol/bibliografia-1/hipotesis%20del%20hidrogeno%20para%20el%20primer%20eucariota.pdf hydrogen hypothesis].
These last two problems are accounted for by the [http://www.fbmc.fcen.uba.ar/materias/genmol/bibliografia-1/hipotesis%20del%20hidrogeno%20para%20el%20primer%20eucariota.pdf hydrogen hypothesis].
== History ==
The endosymbiotic theory was first articulated by famed [[Russian]] botanist Konstantin Mereschkowski in 1905<ref>Mereschkowski C (1905). "Über Natur und Ursprung der Chromatophoren im Pflanzenreiche". Biol Centralbl 25: 593–604.</ref>. Mereschkowski based his theory in part on work done by botanist Andreas Schimper, who had observed in 1883 that the division of chloroplasts in green [[plants]] closely resembled that of cyanobacteria. Schimper had himself tentatively proposed (in a footnote) that green plants could have arisen from the symbiosis of two simpler organisms.<ref>Schimper AFW (1883). "Über die Entwicklung der Chlorophyllkörner und Farbkörper". Bot. Zeitung 41: 105–14, 121–31, 137–46, 153–62.</ref> In the 1920s, Irvin Wallin, a [[professor]] at the University of Colorado Medical School, extended the idea of an endosymbiotic origin to the mitochondria.<ref>Wallin IE (1923). "The Mitochondria Problem". The American Naturalist 57 (650): 255–61. doi:10.1086/279919.
</ref> These theories were initially dismissed (or ignored) by the scientific community. More detailed electron microscopic comparisons between cyanobacteria and chloroplasts (for example, studies by Hans Ris<ref>Ris H, Singh RN (January 1961). "Electron microscope studies on blue-green algae". J Biophys Biochem Cytol 9 (1): 63–80. doi:10.1083/jcb.9.1.63. PMC 2224983. PMID 13741827.</ref>) combined with the discovery that plastids and mitochondria contain their own [[DNA]]<ref>Stocking C and Gifford E (1959). "Incorporation of thymidine into chloroplasts of Spirogyra". Biochem. Biophys. Res. Comm. 1 (3): 159–64. doi:10.1016/0006-291X(59)90010-5.
</ref> (which had recently been identified as the hereditary material of organisms) led to a resurrection of the idea in the 1960s.
The endosymbiotic theory is part of a large body of evidence supporting the [[theory of evolution]]. Prominent evolutionary biologist [[Richard Dawkins]] had the following to say of Lynn Margulis and her work:
The endosymbiotic hypothesis was advanced and substantiated with [[microbiology|microbiological]] evidence in 1967 by [[American]] biologist Lynn Margulis. A young faculty member at [[Boston University]], Margulis authored a theoretical paper entitled ''The Origin of Mitosing Eukaryotic Cells''<ref>Lynn Sagan (1967). "On the origin of mitosing cells". J Theor Bio. 14 (3): 255–274. doi:10.1016/0022-5193(67)90079-3. PMID 11541392.</ref>. The paper, however, was "rejected by about fifteen scientific journals," Margulis recalled<ref>John Brockman, The Third Culture, New York: Touchstone, 1995, 135.</ref>(see [[Best of the Public]]). It was finally accepted by ''The Journal of Theoretical Biology'' and is considered today a landmark in modern endosymbiotic theory. Drawing heavily from the ideas of Mereschkowski and Wallin, Margulis's endosymbiotic theory formulation is the first to rely on direct microbiological observations as opposed to [[paleontology|paleontological]] or [[zoology|zoological]] observations, which were previously the norm for new works in [[evolutionary 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|Earth's]] atmosphere. However, it now appears that they may be formed ''de novo'', contradicting the idea that they have a symbiotic origin<ref>Gabaldón T, Snel B, van Zimmeren F, Hemrika W, Tabak H, Huynen MA (2006). "Origin and evolution of the peroxisomal proteome". Biol. Direct 1 (1): 8. doi:10.1186/1745-6150-1-8. PMC 1472686. PMID 16556314. (Provides evidence that contradicts an endosymbiotic origin of peroxisomes. Instead it is suggested that they evolutionarily originate from the Endoplasmic Reticulum)</ref>. It is believed that over millennia these endosymbionts transferred some of their own DNA to the host cell's nucleus during the evolutionary transition from a symbiotic community to an instituted eukaryotic cell (called "serial endosymbiosis"). This hypothesis is thought to be possible because it is known today from scientific observation that transfer of DNA occurs between [[bacteria]] species, even if they are not closely related. Bacteria can take up DNA from their surroundings and have a limited ability to incorporate it into their own [[genome]].
== See Also ==
== See Also ==
* [[Theory of Evolution]]
* [[Theory of Evolution]]
* [[Theory of Evolution and Cases of Fraud, Hoaxes and Speculation]]
* [[Evolution, Liberalism, Atheism, and Irrationality]]
* [[Evolutionism]]
* [[Symbiosis]]
* [[Symbiosis]]
* [[Cell]]
* [[Cell]]
== References ==
== References ==