Endosymbiosis is an ecological relationship that occurs when an organism lives inside another.
The word endosymbiosis is derived from the Greek, endo "In and symbiosis “living together”, that is, it means an organism living inside the other.
Endosymbiosis Theory
THE Theory of Endosymbiosis or Sequential Endosymbiosis was proposed by microbiologist Lynn Margulis, in the 60s. It was highly contested until it was accepted by the scientific community.
According to this theory, mitochondria and chloroplasts are descended from primitive bacteria that lived inside primitive eukaryotic cells millions of years ago.
For this, a primitive eukaryotic cell encompassed, by phagocytosis, an autotrophic prokaryote cell, which started to live in its cytoplasm.
Eukaryotic cells began to consume oxygen gas, while providing shelter and food to the prokaryotic cells.
Thus, the relationship of endosymbiosis was established, in which the two cells were closely related, without being able to live separately from each other.
As a result of this specific relationship and over time, the prokaryotic cells would have been transformed into mitochondria and chloroplasts.
This endosymbiosis relationship was fundamental for the development of living beings. Eukaryotic cells endowed with mitochondria enabled the emergence of protozoa, fungi and animals.
Evidence of Endosymbiosis Theory
The Endosymbiosis Theory is based on the genetic and biochemical similarities that mitochondria and chloroplasts have in common with certain bacteria.
Mitochondria and bacteria are approximately the same size.
Mitochondria and chloroplasts have their own DNA, different from that existing in the cell nucleus of eukaryotic cells. The DNA of the two organelles is circular, able to duplicate itself and not associated with histones, similar to the pattern found in bacteria.
Mitochondria and chloroplasts synthesize some of their own proteins, much like prokaryotic organisms.
The two organelles are covered by a double membrane and have an internal membrane system, presenting a level of organization in their structures.
To learn more, read also:
Mitochondria;
Chloroplasts.