Endosymbiotic hypothesis

According to the endosymbiotic hypothesis, the eukaryotes used genes from both bacteria (alpha-protobacteria) and cyanobacteria. The first led to the development of mitochondria, the second to that of chloroplasts, i.e., cell organelles which are highly important for energy production (ATP synthesis) and photosynthesis. 

Discussion of the endosymbiotic hypothesis in the light of modern endosymbiotic anaerobic organisms. 

The PolyP metabolism in eukaryotic cells has specific peculiarities in each cellular compartment. For example, a large amount of evidence has been obtained for yeast, suggesting that the synthesis and degradation of PolyP in each specialized organelle and compartment of the cells is mediated by different sets of enzymes. This is consistent with the endosymbiotic hypothesis of eukaryotic cell origin. 

At present, transmembrane /1-barrel proteins have been found exclusively in the outer membrane of gram-negative prokaryotes these membranes seem to lack a-helical proteins. Accordingly, a separation exists between a-proteins in all cytoplasmic membranes and /1-proteins in the specialized outer membranes. Following the endosymbiotic hypothesis, /1-proteins are also expected in the outer membranes of mitochondria and chloroplasts, butnone of these proteins has yet been structurally elucidated. Given the limited abundance of such membranes, the /1-proteins are likely to make up only a small, special class of membrane proteins. 

Kellner RLL. What is the basis of pederin polymorphism in Paedems riparius rove beetles The endosymbiotic hypothesis. Entomol. Exp. Appl. 1999 93 41-49. 

The endosymbiotic hypothesis is supported by a considerable amount of indirect evidence. 

The first eukaryotes are believed to have evolved at least 1.5 billion years ago. The transition from ancient prokaryotic to eukaryotic cell structure is arguably the most important one in evolution, except for the origin of life itself. The endosymbiotic hypothesis is an interesting and compelling view of this transition. 

List six pieces of evidence that support the endosymbiotic hypothesis. 

The endosymbiotic hypothesis proposes that mitochondria and chloroplasts are derived from aerobic bacteria. Is there any structural feature of these organelles that precludes their having been developed by eukaryotic cells ... 

The evidence that supports the endosymbiotic hypothesis includes the following ... 

The existence of mitochondrial DNA, ribosomes, and tRNAs supports the hypothesis of the endosymbiotic origin of mitochondria (see Fig. 1-36), which holds that the first organisms capable of aerobic metabolism, including respiration-linked ATP production, were prokaryotes. Primitive eukaryotes that lived anaerobically (by fermentation) acquired the ability to carry out oxidative phosphorylation when they established a symbiotic relationship with bacteria living in their cytosol. After much evolution and the movement of many bacterial genes into the nucleus of the host eukaryote, the endosymbiotic bacteria eventually became mitochondria. 

Compact review of the endosymbiotic origin hypothesis and the evidence for and against it. 

---