Endosymbiosis
The idea that mitochondria and chloroplasts began as free-living bacteria swallowed by an ancestral cell. Evidence: they have their own circular DNA, bacteria-sized ribosomes and double membranes.
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Analogy
A lodger who moved in, paid rent in energy and never left.
In practice
Mitochondria divide on their own inside the cell, much like bacteria do.
Practice
Flashcards
- Give two pieces of evidence for endosymbiosis.Mitochondria and chloroplasts have their own circular DNA and bacteria-like ribosomes. They also have double membranes.
Interview questions
- Describe the evidence that mitochondria arose by endosymbiosis.
- Own circular DNA
- Bacteria-like ribosomes
- Double membrane
- Divide independently by fission-like process
Questions people ask
Which organelles came from endosymbiosis?
Mitochondria came from a bacterium that could use oxygen to make energy. Chloroplasts came later, from a photosynthetic cyanobacterium swallowed by a cell that already had mitochondria. That is why plants and algae have both, while animals and fungi have only mitochondria.
Why do mitochondria have their own DNA?
Because they were once independent bacteria. Over time most of their genes moved to the nucleus, but a small genome remained. In humans it has 37 genes, and it is inherited almost entirely from the mother because sperm mitochondria are generally destroyed after fertilisation.