The Endosymbiotic Theory

The discussion of the origin of cells, which were mentioned in the latest post, involves many aspects including prokaryotic and eukaryotic cells. It is very likely that the first cells were prokaryotes, considering their simplicity compared to their eukaryotic counterparts. Still, the origin of eukaryotic cells is better understood. The endosymbiotic theory, which incorporates double membrane structure of organelles and DNA, explains how eukaryotic cells first originated.

Mitochondria and chloroplasts play a large role in this theory. It is suggested that these two organelles were prokaryotes that were taken – through endocytosis – in by larger prokaryotes. Normally substances entering the cell are digested and broken down, but these cells remained in their host cells. Eventually mitochondria carried out aerobic respiration and provided energy into their host cell while chloroplast converted light energy to chemical energy. Here are specific details that serve as evidence for the endosymbiotic theory:

• Mitochondria and chloroplasts have double membranes, which supports that they were taken in by endocytosis.
• They have singular naked DNA, 70S ribosomes, and divide by binary fission as do prokaryotic cells.

I have included a diagram that further elaborates on the endosymbiotic theory.

Endosymbiotic Theory (Bioninja)

Works Cited

“Brent Cornell.” BioNinja, ib.bioninja.com.au/standard-level/topic-1-cell-biology/15-the-origin-of-cells/endosymbiosis.html.