endosymbiont hypothesis

biochemistry

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June 17, 2026

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The endosymbiont hypothesis explains the origin of mitochondria and chloroplasts within eukaryotic cells. It proposes that these organelles were once free-living prokaryotes that were engulfed by an ancestral host cell.12

Over time, a symbiotic relationship developed. The host cell provided protection and nutrients, while the engulfed prokaryotes generated energy. Mitochondria, found in both plant and animal cells, produce adenosine triphosphate (ATP) through cellular respiration. Chloroplasts, present in plant and algal cells, capture light energy to produce carbohydrates and ATP through photosynthesis.12

Evidence supporting this theory includes the organelles' double membranes, circular DNA, and ribosomes, which are similar to those of prokaryotes. This evolutionary event was crucial for the development of complex eukaryotic cells.12

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The endosymbiont hypothesis
Mitochondria and chloroplasts are self-dividing; they contain their own DNA and protein-synthesizing machinery, similar to that of prokaryotes. Chloroplasts produce ATP and trap photons by mechanisms that are complex and yet similar to those of certain prokaryotes. These phenomena have led to the…
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Mitochondria and chloroplasts are self-dividing; they contain their own DNA and protein-synthesizing machinery, similar to that of prokaryotes. Chloroplasts produce ATP and trap photons by mechanisms that are complex and yet similar to those of certain prokaryotes. These phenomena have led to the…
Read More