Question

what evidence is there that mitochondria and chloroplasts originated from ancient prokaryotes and why?

Answer 1

The endosymbiotic theory deals with the origins of mitochondria and chloroplasts, two eukaryotic organelles that have bacteria characteristics. Mitochondria and chloroplasts are believed to have developed from symbiotic bacteria, specifically alpha-proteobacteria and cyanobacteria, respectively.  The theory states that a prokaryotic cell was consumed or engulfed by a larger cell. By some unknown reason, the prokaryotic organelle was not consumed. Such lack of consumption would later lead to both cells forming a mutualism, receiving surviving benefits from each other. Over time, the newly combined organelle would develop into the complex eukaryotic cell of today.

Chloroplast is only found in plants while majority of eukaryotic cells have mitochondria. Even though both organelles are found in eukaryotic cells, both mitochondria and chloroplast have characteristics often found in prokaryotic cells.

Modern scientists believe that certain organelles found exclusively in eukaryotic cells may have arisen from various prokaryotic ancestors that initiated endosymbiotic relationships with host cells that consumed them. This belief is supported by evidence such as the discovery of DNA and ribosomes within organelles like mitochondria and chloroplasts.

For example, each organelle in eukaryotes has a single, circular DNA that is more similar to prokaryotes than eukaryotes.

Furthermore, the existence of double membranes over many of these organelles suggests the possibility that the inner membrane may have belonged to the original prokaryote while the outer membrane may have formed from food vacuoles as the host cell devoured the prokaryote. The inner membrane of these organelles contains enzymes and transport systems that are similar to the plasma membrane of prokaryotes.