The hydrogen hypothesis is a model proposed by William F. Martin and Miklós Müller in 1998 that describes a possible way in which the mitochondrion arose as an endosymbiont within a prokaryote (an archaeon), giving rise to a symbiotic association of two cells from which the first eukaryotic cell could have arisen.
According to the hydrogen hypothesis:
- The host that acquired the mitochondrion was a prokaryote, a hydrogen-dependent archaeon, possibly similar in physiology to a modern methanogenic archaea which uses hydrogen and carbon dioxide to produce methane;
- The future mitochondrion was a facultatively anaerobic eubacterium which produced hydrogen and carbon dioxide as byproducts of anaerobic respiration;
- A symbiotic relationship between the two started, based on the host's hydrogen dependence (anaerobic syntrophy).
The hypothesis differs from many alternative views within the endosymbiotic theory framework, which suggest that the first eukaryotic cells evolved a nucleus but lacked mitochondria, the latter arising as a eukaryote engulfed a primitive bacterium that eventually became the mitochondrion.
The hypothesis attaches evolutionary significance to hydrogenosomes and provides a rationale for their common ancestry with mitochondria. Hydrogenosomes are anaerobic mitochondria that produce ATP by, as a rule, converting pyruvate into hydrogen, carbon dioxide and acetate. Examples from modern biology are known where methanogens cluster around hydrogenosomes within eukaryotic cells. Most theories within the endosymbiotic theory framework do not address the common ancestry of mitochondria and hydrogenosomes.
The hypothesis provides a straightforward explanation for the observation that eukaryotes are genetic chimeras with genes of archaeal and eubacterial ancestry. Furthermore, it would imply that archaea and eukarya split after the modern groups of archaea appeared. Most theories within the endosymbiotic theory framework predict that some eukaryotes never possessed mitochondria. The hydrogen hypothesis predicts that no primitively mitochondrion-lacking eukaryotes ever existed. In the 10 years following the publication of the hydrogen hypothesis, this specific prediction has been tested many times and found to be in agreement with observation.
Other articles related to "hydrogen hypothesis, hypothesis, hydrogen":
... One hypothesis on how gas could have leaked is that one of the many bracing wires within the airship snapped and punctured at least one of the internal gas ... Advocates of this hypothesis believe that the hydrogen began to leak approximately five minutes before the fire ... A punctured cell would have freed hydrogen into the air and could have been ignited by a static discharge (see above), or it is also possible that the broken bracing wire ...
... the hypotheses can be categorized as – the serial endosymbiotic theory (SET), the hydrogen hypothesis (mostly a process of symbiosis where hydrogen ... In the hydrogen hypothesis, the symbiotic linkage of an anaerobic and autotrophic methanogenic archaeon (host) with an alpha-proteobacterium (the symbiont) gave rise ... The host utilized hydrogen (H2) and carbon dioxide (CO2) to produce methane while the symbiont, capable of aerobic respiration, expelled H2 and CO2 as byproducts ...
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