The endosymbiotic theory is about the origins of mitochondria and chloroplast, which are organelles of eukaryotic cells. Eukaryotic cells are cells that have a nucleus and prokaryotic cells are cells that do not have a nucleus. The theory states that mitochondria of eukaryotic cells evolved from aerobic bacteria living within their host cell. The chloroplasts of eukaryotic cells evolved from endosymbiotic autotrophic prokaryotes. The theory is now generally worldly accepted due to the evolution explanation.
Mitochondria evolved from small heterotrophic that were engulfed by a larger eukaryotic cell, where membrane infolding had occurred. The smaller cell used cellular respiration to take in oxygen and convert this into energy, this are to small to ingest so live within the host cell. So therefore as the theory applies , these cells would have been more productive because of the endosymbiotic relationship that they had and multiplied more producing eukaryotic cells and eventually leading to all eukaryotic.
Scientist believe that chloroplast probably evolved to that similar to mitochondria, however chloroplast probably were ingested by only some eukaryotic cells and were ingested after the first mitochondria. This is why almost all eukaryotic cells have mitochondria but only some have chloroplast. Eventually the mitochondria and the chloroplasts became so interdependent that they became organelles of the host cell.
There is a lot of evidence to back up this theory. Mitochondria and chloroplast can arise only for preexisting mitochondria and chloroplast and cannot be formed in a cell that lacks them because nuclear genes encode only some of the proteins of which they are made. They both also have their own genome, which resembles that of a prokaryotic cell that is not that of the nuclear genome and both consist of a single circular molecule of DNA. DNA is not found in any other type of organelle, only mitochondria and chloroplast this is another piece of evidence, which backs up the endosymbiotic theory. Another key piece of evidence is that both mitochondria and chloroplast have their own protein-synthesizing machinery, and they both resemble the prokaryotic cells not found in the cytoplasm of eukaryotic cells.
The scientific evidence that mitochondria and chloroplast arose via an ancient endsymbiosis of bacteria is that both mitochondria and chloroplast contain DNA, which is fairly different from that of the cell nucleus. Also that they are surrounded by two or more membranes. The DNA sequence suggests that nuclear DNA contains genes that probably came from the chloroplast, which further more proves this theory.
There are many scientific discoveries that support the endosymbiotic theory of evolution, for example mitochondria and chloroplast both contain DNA and RNA and ribosome’s which are all similar to those of prokaryotic cells. Also mitochondria and chloroplast each have two membranes, the outer one probably is a product of membrane infolding by the host cell, but the inner one is probably the ancestral prokaryotes plasma membrane. This is supported by the fact that enzymes and other proteins in the inner membrane resemble their counterparts in prokaryotic cells. Other similarities between these organelles and prokaryotic cells include division by binary fission and DNA replication, transcription and translation.
