Mitochondria and chloroplasts run mostly on nuclear genes
- The idea
- Predict
- See it
- Why
- Check
The idea
“Mitochondria and chloroplasts have their own DNA, so they make most of their own proteins.”
Mitochondria have their own DNA and ribosomes, so it's natural to picture them building their own parts. Their DNA is tiny, though.
The short version
The mistake: Mitochondria and chloroplasts have their own DNA, so they make most of their own proteins.
What's actually true: Most of their proteins are coded by genes in the nucleus, made in the cytosol, and imported into the organelle.
- Mitochondria and chloroplasts descend from bacteria that an ancient host cell took in. That's endosymbiosis, and it's why they still have their own DNA.
- Over time, many of those bacterial genes moved into the host's nucleus. Each organelle kept only a small set.
- Ribosomes in the cytosol now build those proteins, and the organelle imports them across its membranes.
On the exam: Organelle DNA is small. Most mitochondrial and chloroplast proteins come from nuclear genes and get imported.