Biology, 19.02.2020 20:14 nborowy9579

According to the endosymbiosis theory of the origin of eukaryotic cells, how did mitochondria originate?

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The endosymbiotic theory proposes that mitochondria and chloroplasts were once free-living bacteria. Mitochondria originated from bateria like rickettsias that were phagocyted but not digested by the bigger cell.

The endosymbiotic theory proposes that mitochondria and chloroplasts were once free-living bacteria that were phagocytized by another cell but not digested.

These bacteria got to adapt to their host, and both cells became interdependent.

Both organelles have many similarities with other free-living bacteria.

Chloroplasts probably derivate from cyanobacteria because both cells absorb sunlight, produce ATP and organic molecules.

Mitochondria derivate from rickettsias because they produce ATP in the same way by using the Krebs Cycle and Oxidative Phosphorylation.

From the phagocytosis moment, these two cells became so dependant on each other they could not survive without the other one.

Chloroplasts and mitochondria share some traits with free-living bacteria that support the theory.

• Both organelles present their genetic material. This DNI is independent of the cells´ DNA, is bi-catenary and circular, identical to the bacterial DNA, and very different from the one of the eukaryotic cells.

• Both organelles divide by binary fission (not by mitosis) and can synthesize their ribosomes and organelles.

• Both organelles present a double membrane, a characteristic that reinforces the idea of being phagocyted.

The internal membrane looks identical to the bacterial membrane, while the external membrane looks like the eukaryotic one.

In fact, in this internal membrane are placed the energy centers, just as it occurs in bacterias membrane.

• Finally, the sizes of the organelles are similar to the size of some procaryotes.

According to the endosymbiosis theory of the origin of eukaryotic cells, mitochondria originated from a rickettsia that was phagocyted but not digested by the bigger cell.