endosymbiotic theory

The endosymbiotic theory was proposed by Lynn Margulis in 1981 in a book entitled Symbiosis in Cell Evolytion. This theory explains how chloroplasts and mitochondria arose in eukaryotic cells.

→ The endosymbiotic theory

According to the endosymbiotic theory, mitochondria and chloroplasts were free-living prokaryotic organisms. These structures were engulfed by eukaryotic cells, which resulted in a symbiotic relationship, in which both involved benefited from the association.

Mitochondria were probably aerobic prokaryotic organisms, and chloroplasts were photosynthetic prokaryotes. These prokaryotic organisms provided energy for the cell that encompassed them, and the host cell provided protection from the external environment.

→ Points that reinforce the endosymbiotic theory

When analyzing mitochondria and chloroplasts, some characteristics show the similarity between these organelles and prokaryotic organisms, in addition to some points that reinforce the theory that these structures were encompassed in a process of endocytosis. Here’s some of that evidence:

I. Mitochondria and chloroplasts have a double membrane, a result, probably, of the engulfment of these organisms. The innermost would come from the encompassed organism, and the outermost would result from the membrane of the organism that encompassed it;

II. Mitochondria and chloroplasts have their own genome. The DNA of mitochondria and chloroplasts is circular and without proteins called histones;

III. Mitochondria and chloroplasts are capable of self-replication;

IV. The ribosomes found in mitochondria and chloroplasts are similar to those in prokaryotes and different from those found in eukaryotes;

V. Certain antibiotics cause changes in mitochondrial and chloroplast protein synthesis;

SAW. Mitochondria and chloroplasts are similar in size to bacteria.