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Topic: Endosymbiotic hypothesis


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In the News (Tue 25 Jun 19)

  
  Talk:Endosymbiotic hypothesis - Wikipedia, the free encyclopedia
Currently, I think the evidence I offer in support of the Endosymbiotic Hypothesis is fairly weak, and much of the evidence seems consistent with a variety of other hypotheses.
Ideally, this article should cite the evidence that more-convincingly indicates that the Endosymbiotic Hypothesis is probably correct, and other hypotheses (like the one I just made up) are significantly less plausible.
This could be expanded on - I think the presence of nucleomorphs in the chloroplasts of cryptomonads and chlorarachniophytes has been considered a spectacular piece of evidence for the endosymbiotic hypothesis, though it shows chloroplasts secondarily derived from eukaryotic rather than prokaryotic ancestors.
www.wikipedia.org /wiki/Talk:Endosymbiotic_hypothesis   (771 words)

  
 Endosymbiotic hypothesis: Definition and Links by Encyclopedian.com - All about Endosymbiotic hypothesis   (Site not responding. Last check: 2007-11-06)
The Endosymbiotic Hypothesis is a hypothesis about the origins of mitochondria and chloroplasts, which are organelles of eukaryotic cells.
The hypothesis postulates that the mitochondria evolved from aerobic bacteria (probably proteobacteria, related to the rickettsias), that the chloroplast evolved from endosymbiotic cyanobacteria (autotrophic prokaryotes).
Margulis has also proposed that eukaryotic flagella and cilia may have arisen from endosymbiotic spirochetes, but these organelles do not contain DNA and do not show any ultrastructural similarities to any prokaryotes, and as a result this idea does not have wide support.
www.encyclopedian.com /en/Endosymbiotic-hypothesis.html   (705 words)

  
 Endosymbiotic theory - Wikipedia, the free encyclopedia
The endosymbiotic theory concerns the origins of mitochondria and chloroplasts, which are organelles of eukaryotic cells.
The theory postulates that the mitochondria evolved from facilitated anaerobic bacteria (probably proteobacteria, related to the rickettsias), and that the chloroplast evolved from endosymbiotic cyanobacteria (autotrophic prokaryotes).
The endosymbiotic hypothesis was popularized by Lynn Margulis.
en.wikipedia.org /wiki/Endosymbiotic_hypothesis   (742 words)

  
 Endosymbiotic theory - EvoWiki   (Site not responding. Last check: 2007-11-06)
The Endosymbiotic theory states that the cellular organelles mitochondria and chloroplasts (more generally, plastids) of eukaryotic cells were originally free living prokaryotic organisms.
A seeming difficulty with the endosymbiosis hypothesis is the fact that several mitochondrial and chloroplast proteins are made using nuclear genes and then shipped to those respective organelles.
Gene loss is also known to have happened in other endosymbiotic organisms, like Buchnera aphidicola, a symbiont of aphids that supplies "essential" amino acids and other nutrients to their hosts, and Rickettsia prowazekii, which causes the disease typhus.
wiki.cotch.net /wiki.phtml?title=Endosymbiotic_theory   (1465 words)

  
 Mitochondrion
Because of the unique matrilineal transmission of mitochondrial DNA, scientists in population genetics and evolutionary biology often use data from mitochondrial DNA sequences to draw conclusions about genealogy and evolution.
These and similar pieces of evidence motivate the endosymbiotic hypothesis — that mitochondria originated as prokaryotic endosymbionts.
Essentially this widely accepted hypothesis postulates that the ancestors of modern mitochondria were independent bacteria that colonized the interior of the ancient precursor of all eukaryotic life.
publicliterature.org /en/wikipedia/m/mi/mitochondrion.html   (885 words)

  
 Evolution of flagella - EvoWiki   (Site not responding. Last check: 2007-11-06)
The modern version of the hypothesis was first proposed by Lynn Margulis as Sagan (1967) (Margulis was the first wife of the late Carl Sagan).
The only real point in favor of the symbiotic hypothesis is that there apparently actually are eukaryotes that use symbiotic spirochetes as their motility organelles (only inside termite guts (http://occ.awlonline.com/bookbind/pubbooks/tfc/medialib/Applications/termites.html), though, as far as I know).
At present the symbiotic hypothesis for the origin of cilia seems to be basically a pet idea of Margulis and a few of her associates.
www.evowiki.org /wiki.phtml?title=Evolution_of_flagella   (5776 words)

  
 Two-source hypothesis   (Site not responding. Last check: 2007-11-06)
The Two-Source Hypothesis was first articulated in 1838 by Christian Hermann Weisse, but it did not gain wide acceptance among German critics until Heinrich Julius Holtzmann endorsed it in 1863.
The Two-Source Hypothesis crossed the channel into England in the 1880s primarily due to the efforts of William Sanday, but it was Burnett Hillman Streeter who definitively expressed the case in 1924.
The Griesbach hypothesis continues to be the main challenger to the Two-Source Hypothesis in America, primarily due to the efforts of William R. Farmer (1965), but in England its most influential opponents favor the Farrer hypothesis (Mark → Matthew → Luke).
www.information-and-answers.com /resource-Two-source_hypothesis.html   (214 words)

  
 Changing perspectives on the origin of eukaryotesLaura A
Finally, analyses of hydrogenosomes have led to the hypothesis that these organelles are highly modified relatives of extant mitochondria303132.
The implications of the loss of the kingdom Archezoa are profound: instead of a stepwise model of the evolution of eukaryotes, in which the nucleus and microtubules evolved before the acquisition of mitochondria, we must now consider the possibility that the nuclei, mitochondria and microtubules of eukaryotes had a simultaneous origin.
It is now possible to assume that the original endosymbiotic event that gave rise to the mitochondria (whether for respiration40, hydrogen-dependent metabolism42 or sulfur-dependent metabolism43) occurred in the ancestor of all extant eukaryotes, and that this endosymbiosis explains both the chimeric nature of eukaryotic genomes and the origin of mitochondria.
cas.bellarmine.edu /tietjen/Ecology/changing_perspectives_on_the_ori.htm   (3213 words)

  
 General Biology Exam #1-Fall 2001   (Site not responding. Last check: 2007-11-06)
16.___D__The endosymbiotic hypothesis argues that prokaryotes became some of the organelles of early eukaryotic cells.
To be valid, a hypothesis should lead to a predicted result.
Hypothesis testing is a form of deductive reasoning.
www.franklincollege.edu /bioweb/gbsb/ex1f01.htm   (1351 words)

  
 Eukaryota History Summary   (Site not responding. Last check: 2007-11-06)
The endosymbiotic hypothesis for the origin of eukaryotic cells was first proposed by Lynn Margulis in her 1981 book, Symbiosis in Cell Evolution.
The endosymbiotic hypothesis ("endo" means "within," "symbiosis" is a situation in which organisms live together in close association) suggests that eukaryotic cells arose when certain prokaryotic cells acquired endosymbionts, in this case other prokaryotic cells that lived within them.
It is believed that the endosymbionts derived benefits from the host such as protection and organic nutrients, while the host obtained ATP (from the prokaryotes which evolved into mitochondria) or access to the products of photosynthesis (from the prokaryotes which evolved into chloroplasts).
www.bookrags.com /history/biology/eukaryota-ansc-02   (571 words)

  
 Brainstorms: Endosymbiosis and science
When Margulis revived Wallin's hypothesis, she pointed to the newly discovered facts that indicated mitochondria had their own DNA and the mitochondria replicated rather than formed de novo.
Suffice it to say that the main thrust of her hypothesis has been rejected by mainstream science, where endosymbiosis currently accounts for the origin of mitochondria and chloroplasts, not eukarya (although some now favor a symbiosis these between archaea and eubacteria).
I mention all this not in any attempt to discredit Margulis and her hypothesis, but to illustrate that some have a tendency to forget the failed predictions and remember the successful ones.
www.iscid.org /boards/ubb-get_topic-f-6-t-000236.html   (1064 words)

  
 The Emergence of Complex Life
This endosymbiotic hypothesis may explain the evolution of more complex cell structures from simpler cell precursors.
The endosymbiotic hypothesis suggests a mechanism for the evolution of cell complexity.
It is important to appreciate that an amazing amount of evolution precedes the point in time, roughly 600 million years ago, when the fossil record that we recognize from our visits to museums begins to chronicle the evolution of higher life forms.
www.globalchange.umich.edu /globalchange1/current/lectures/complex_life/complex_life.html   (2642 words)

  
 MSN Encarta - Search Results - endosymbiotic hypothesis
Hypothesis, a preliminary assumption or tentative explanation that accounts for a set of facts, taken to be true for the purpose of investigation and...
Big Bang Theory, hypothesis on the origin of the universe
identifying a hypothesis, negating a hypothesis, testing for true statements, writing a hypothesis, writing conditional statements
encarta.msn.com /endosymbiotic+hypothesis.html   (163 words)

  
 Internal Structure of a Neuron - Mitochondria   (Site not responding. Last check: 2007-11-06)
It is estimated that the first of living cells, prokaryotes, emerged approximately 3.5 billion years ago (Arms and Camp, 1995).
A popularly held belief, the endosymbiotic hypothesis, holds that eukaryotic cell arose from prokaryotic cells.
The endosymbiotic hypothesis was generated in part in an attempt to explain the finding that mitochondria contain their own genetic material, DNA and RNA molecules.
psych.athabascau.ca /html/Psych402/Biotutorials/1/mitochondria.shtml   (227 words)

  
 Endosymbiont   (Site not responding. Last check: 2007-11-06)
It is generally believed that certain organelles of the eukaryotic cell, especially mitochondria and chloroplasts, originated as bacterial endosymbionts.
This theory is known as the endosymbiotic hypothesis.
Nancy A. Moran (1996), Accelerated evolution and Muller’s ratchet in endosymbiotic bacteria, Proceedings of the National Academy of Sciences of the USA, 93, pp.
www.sciencedaily.com /encyclopedia/endosymbiont   (783 words)

  
 Encyclopedia: Endosymbiotic-theory   (Site not responding. Last check: 2007-11-06)
Konstantin Sergivich Merezhkovsky (1855-1921) (also transliterated Konstantin Sergeevich Merezhkovsky, Constantin Sergeevič Mérejkovski, Constantin Sergejewicz Mereschcowsky, Konstantin Sergejewicz Mereschkovsky and Konstantin Sergejewicz Mereschkowsky) 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, more complex...
A flagellum (plural, flagella) is a whip-like organelle that many unicellular organisms, and some multicellular ones, use to move about.
The Hydrogen hypothesis is a model that describes how the first eukaryotic cell may have developed.
www.nationmaster.com /encyclopedia/Endosymbiotic_theory   (1431 words)

  
 Read about Endosymbiotic theory at WorldVillage Encyclopedia. Research Endosymbiotic theory and learn about ...   (Site not responding. Last check: 2007-11-06)
proteobacteria, related to the rickettsias), and that the chloroplast evolved from endosymbiotic
According to Margulis and Sagan (1996), "Life did not take over the globe by combat, but by networking" (i.e., by cooperation), and Darwin's notion of evolution driven by competition is incomplete.
peroxisomes may have an endosymbiotic origin has also been considered, although they lack DNA.
encyclopedia.worldvillage.com /s/b/Endosymbiotic_theory   (671 words)

  
 E words.
The process by which cells take in bulk material from the outside, usually by surrounding the material and isolating it into a vacuole or vesicle which is then brought deeper into the cell.
This hypothesis says that certain organelles, chiefly mitochondria and plastids, evolved from free living bacteria that became symbiotic with the ancestors of modern eukaryotic cells.
Experiments usually involve comparing a control group with an experimental group where the two groups are as similar as possible except that the experimental group receives a treatment not given to the control group.
staff.jccc.net /pdecell/bio122/words/edefs.html   (947 words)

  
 Basics of Cellular Functional Anatomy   (Site not responding. Last check: 2007-11-06)
In the 1960's and 70's biologists led by Lynn Margulis championed the endosymbiotic hypothesis.
In this hypothesis chloroplasts and mitochondria had their origin as prokaryotes that were engulfed by an ancestor to modern eukaryotic cells.
The endosymbiotic hypothesis is currently favored by most biologists.Some evidence for this hypothesis is given below.
www.users.csbsju.edu /~dgbrown/BIOL116/Notes/Cells_Work.html   (3399 words)

  
 Protists   (Site not responding. Last check: 2007-11-06)
Endosymbiotic hypothesis—symbiotic associations of prokaryotes may have resulted in the appearance of cellular organelles and ultimately eukaryotic cells
              The endosymbiotic hypothesis states that eukaryotic organisms originated from symbiotic associations of prokaryotes, which may have resulted in the appearance of cellular organelles, such as mitochondria and chloroplasts.
There seems to be greater support for the endosymbiotic hypothesis.
acad.udallas.edu /biology/GenBio/Protists.html   (1377 words)

  
 Ch. 30
However, the origin of mitochondria, chloroplasts, and perhaps even flagella and cilia, may be explained by the endosymbiotic hypothesis.
The endosymbiotic hypothesis explains origin of mitochondria, chloroplasts, and perhaps flagella and cilia.
It proposes that aerobic heterotrophic bacteria became mitochondria, and cyanobacteria became chloroplasts (and perhaps spirochetes became flagella and cilia) after being taken up by eukaryotic cells and the prokaryotic and eukaryotic cells developing symbiotic relationships.
howard.nebrwesleyan.edu /hhmi/fellows/awasmoen/mader30.html   (2789 words)

  
 Endosymbiotic Theory
Although now accepted as a well-supported theory, both she and the theory were ridiculed by mainstream biologists for a number of years.
Thanks to her persistance, and the large volumes of data that support this hypothesis gathered by her and many other scientists over the last 30 years, biology can now offer a plausible explanation for the evolution of eukaryotes.
Further, in the late 1980's a team of Rockefeller University investigators announced their similar discovery regarding centrioles, structures that provide the eukaryotic cell with the ability of locomotion and cell division.
www.biology.iupui.edu /biocourses/N100/2k2endosymb.html   (767 words)

  
 Telic Thoughts » Endosymbiotic Theory   (Site not responding. Last check: 2007-11-06)
According to the endosymbiotic theory, mitochondria are the descendents of bacteria.
Suffice it to say that the main thrust of her hypothesis has been rejected by mainstream science, where endosymbiosis currently accounts for the origin of mitochondria and chloroplasts, not eukarya (although many now favor a symbiosis between archaea and eubacteria).
I mention all this not in any attempt to discredit Margulis and her hypothesis (as I accept them), but to illustrate that some have a tendency to forget the failed predictions and remember the successful ones.
telicthoughts.com /?p=242   (1796 words)

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