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What evidence supports the idea that mitochondria evolved from ancient bacteria?
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mitochondrion
Mitochondria (red) are found throughout the cytoplasm of almost all eukaryotic cells (cell nucleus is shown in blue; cytoskeleton is shown in yellow).
The theory that mitochondria evolved from ancient bacteria—specifically through a process known as endosymbiosis—is supported by several key lines of evidence:
- Genetic Material: Mitochondria contain their own circular DNA, which is structurally similar to the DNA found in prokaryotes rather than the linear chromosomes found in the eukaryotic nucleus.123
- Reproduction: These organelles replicate independently of the cell’s nuclear DNA through binary fission, a method of division characteristic of bacteria.124
- Membrane Structure: Mitochondria possess two distinct membranes, with the structure of these membranes resembling those of prokaryotic organisms.123
- Protein Synthesis: Mitochondria contain bacteria-like ribosomes, which are essential for the protein-synthesizing machinery required for their function.53
According to the endosymbiotic theory, an ancestral eukaryotic cell engulfed an aerobic bacterium. Instead of being digested, the bacterium formed a mutually beneficial relationship with the host, eventually becoming permanently integrated as an organelle that provides energy in the form of ATP.513