endosymbioseteorien

The endosymbiotic theory, or endosymbiosis theory, is a scientific hypothesis that explains the origin of eukaryotic cells. It proposes that certain organelles within eukaryotic cells, specifically mitochondria and chloroplasts, were once free-living prokaryotic organisms. These organisms were engulfed by a larger host cell, but instead of being digested, they established a symbiotic relationship with the host. Over evolutionary time, these engulfed prokaryotes became integrated into the host cell, losing their independence and developing into the organelles we see today.

The evidence supporting this theory is substantial. Mitochondria and chloroplasts possess their own circular DNA, similar to the DNA found in bacteria, which is separate from the nuclear DNA of the eukaryotic cell. They also have their own ribosomes, which are structurally more like prokaryotic ribosomes than eukaryotic ones. Furthermore, these organelles replicate independently of the cell nucleus, through a process akin to binary fission, a common mode of reproduction for bacteria. The double membrane surrounding mitochondria and chloroplasts is also explained by the theory, with the inner membrane originating from the prokaryote's original membrane and the outer membrane coming from the host cell's engulfing vesicle. This theory was notably championed by Lynn Margulis, who significantly contributed to its acceptance in the scientific community.