Endosymbiont hypothesis

Kroemer G (1997a) Mitochondrial implication in apoptosis. Towards an endosymbiont hypothesis of apoptosis evolution. Cell Death Differ 4 443-456 Kroemer G (1997b) The proto-oncogene bcl-2 and its role in regulating apoptosis. Nat... 

A FIGURE 8-3 Evolutionary origin of mitochondria and chloroplasts according to endosymbiont hypothesis. 

According to the endosymbiontic hypothesis mitochondria derive from ancestors that are closely related to modern purple bacteria, for example, Pseudomonas, Rhodobacter, and Paracoccus. Although mitochondria are embedded in a cellular environment with narrowly controlled conditions regarding pH, redox balance, and substrate availability, bacteria may encounter a variety of environmental conditions. A repertoire of respiratory chains and regulatory mechanisms as opposed to a single electron transfer chain allows them to cope with a variety of environments. 

These commonalities between mitochondria, chloroplasts, and bacteria undoubtedly have an evolutionary origin. In bacteria both photosynthesis and oxidative phosphorylation occur on the plasma membrane. Analysis of the sequences and transcription of mitochondrial and chloroplast DNAs (Chapters 10 and 11) has given rise to the popular hypothesis that these organelles arose early in the evolution of eukaryotic cells by endocytosis of bacteria capable of oxidative phosphorylation or photosynthesis, respectively (Figure 8-3). According to this endosymbiont... 

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