One cell can have two kinds of ribosome
- The idea
- Predict
- See it
- Why
- Check
The idea
“Every ribosome in a eukaryotic cell is the same kind, wherever it sits.”
Most people picture one cell making one kind of ribosome. That holds in the cytosol and on the rough ER, but not in mitochondria or chloroplasts.
The short version
The mistake: Every ribosome in a eukaryotic cell is the same kind, wherever it sits.
What's actually true: Cytosol and rough ER ribosomes are eukaryotic. Mitochondria and chloroplasts have their own, more like a bacterium's.
- Free ribosomes and the ones on the rough ER are the same eukaryotic kind. Binding to the ER only changes where the protein goes.
- Mitochondria and chloroplasts have their own DNA and their own smaller ribosomes, more like a bacterium's.
- That fits endosymbiotic theory. Both organelles came from engulfed bacteria and kept bacteria-like ribosomes, circular DNA and a double membrane.
- So some antibiotics aimed at bacterial ribosomes can slow protein synthesis in your mitochondria. Most mitochondrial proteins are still made in the cytosol and imported.
On the exam: Mitochondria and chloroplasts have their own bacteria-like ribosomes. The rest of the cell's are eukaryotic.