Proteins get changed after the ribosome makes them
- The idea
- Predict
- See it
- Why
- Check
The idea
“Any change to a protein, like a sugar or a phosphate, is put on at the ribosome while it's made.”
Making a protein and finishing it both sound like building, so it's easy to credit every step to the ribosome.
The short version
The mistake: Any change to a protein, like a sugar or a phosphate, is put on at the ribosome while it's made.
What's actually true: Ribosomes only link amino acids. Separate enzymes add sugars and phosphates to the protein.
- Translation at the ribosome builds the amino acid sequence. Then the ribosome's job is over.
- Other enzymes add the sugars. A few go on in the ER, and Golgi enzymes trim and add more before the protein is shipped.
- In signaling, kinases add phosphate groups to proteins the cell already has. That changes their shape and activity.
On the exam: Ribosomes link amino acids and nothing else. Sugars and phosphates are added by other enzymes.