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Mitochondria and plastids contain their own ribosomes; these are more similar to those of bacteria (70S) than those of eukaryotes. [74] Proteins created by mitochondria and chloroplasts use N-formylmethionine as the initiating amino acid, as do proteins created by bacteria but not proteins created by eukaryotic nuclear genes or archaea. [75] [76]
The most common examples of obligate endosymbiosis are mitochondria and chloroplasts; however, they do not reproduce via mitosis in tandem with their host cells. Instead, they replicate via binary fission, a replication process uncoupled from the host cells in which they reside.
The theory of endosymbiosis, as known as symbiogenesis, provides an explanation for the evolution of eukaryotic organisms. According to the theory of endosymbiosis for the origin of eukaryotic cells, scientists believe that eukaryotes originated from the relationship between two or more prokaryotic cells approximately 2.7 billion years ago.
Evidence for this includes the fact that mitochondria and chloroplasts divide independently of the cell, and that these organelles have their own genome. [ 73 ] The biologist Lynn Margulis , famous for her work on endosymbiosis , contended that symbiosis is a major driving force behind evolution .
Chloroplasts and mitochondria also replicate semi-autonomously outside of the cell cycle replication system via binary fission. [12] Consistent with the theory, decreased genome size within the organelle and gene integration into the nucleus occurred. Chloroplasts genomes encode 50-200 proteins, compared to the thousands in cyanobacterium. [13]
Like mitochondria, chloroplasts have a double-membrane envelope, called the chloroplast envelope, but unlike mitochondria, chloroplasts also have internal membrane structures called thylakoids. Furthermore, one or two additional membranes may enclose chloroplasts in organisms that underwent secondary endosymbiosis , such as the euglenids and ...
This may include keeping certain biomolecules within a region, or keeping other molecules outside. Within the membrane-bound compartments, different intracellular pH, different enzyme systems, and other differences are isolated from other organelles and cytosol. With mitochondria, the cytosol has an oxidizing environment which converts NADH to ...
Mitochondria were found to be most closely related to the α-purple subdivision of Gram negative bacteria and chloroplasts were most similar to cyanobacteria, similar to other data supporting the endosymbiosis theory. [6] Gram positive bacteria were found to be the most ancestral, which is also supported by other studies. [6]