Question

Mitochondria are unable to survive outside of eukaryotic cells. If they originated from ancestral prokaryotes, as proposed by the endosymbiotic theory, then why can’t they survive independently?

Answer 1

As proposed by the endosymbiotic theory which describes the origin of chloroplast and mitochondria states that once a prokaryotic cell engulfed a free-living prokaryotic cell. The cell somehow survived without being digested and continues to live inside the cell. During the course of evolution, they developed a symbiotic relationship benefitting each other. The host cell provided protection from the outer environment and in turn, the engulfed cell helped with energy production. As time passed, the engulfed cell becomes completely dependent on the host cell and as a result, the genome is reduced to a significant degree as necessary proteins and other supplements were now available from the host cell. We know that mitochondria and chloroplast contain their own closed circular DNA similar to the bacteria but much of their necessary protein-encoding gene is lost and some genes are transferred to the host genome as mitochondria become an organelle. Therefore, due to the loss of its necessary genes, it can not survive on its own if released into the environment.