Origin of organelles Animation

Possible origins of the nucleus and other organelles. Some prokaryotic cells have infoldings of their plasma membrane. These infoldings may have served as channels from the cytoplasm to the cell surface. These membranous folds may have evolved into the endoplasmic reticulum and the nuclear envelope of early eukaryotes. Other organelles may have arisen through endosymbiosis. An ancestral cell may have engulfed an anaerobic, heterotrophic prokaryote. If the small cell was not digested, it may have been able to live, produce ATP, and divide inside its host. Over time, the host cell may have come to rely on ATP production by its endosymbiotic guests. The guests may have evolved into mitochondria. Photosynthetic bacteria also may have been engulfed and become endosymbionts. Over time, their descendants could have been modified so that they eventually became chloroplasts. The endosymbiosis model is supported by strong evidence. The biochemistry of chloroplasts and mitochondria resembles that of some prokaryotes. These organelles also divide independently of cell division using a process that resembles prokaryotic fission.

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