The nucleolus makes ribosomes. Ribosomes make proteins.
- The idea
- Predict
- See it
- Why
- Check
The idea
“The nucleolus is where the cell makes its proteins.”
The nucleolus is the dark spot in every drawing of a nucleus, and it keeps coming up beside protein synthesis. So it seems like proteins come from there.
The short version
The mistake: The nucleolus is where the cell makes its proteins.
What's actually true: The nucleolus assembles ribosome subunits, and the finished ribosomes make proteins out in the cytoplasm.
- In the nucleolus, the cell makes rRNA and packs it with ribosomal proteins into a large and a small subunit.
- The subunits leave through nuclear pores. In the cytoplasm they join on an mRNA and link amino acids into a polypeptide. That's translation.
- Even the ribosomal proteins are made in the cytoplasm, then carried into the nucleus to be packed.
- A cell that makes a lot of protein needs many ribosomes, so its nucleolus tends to be large.
On the exam: The nucleolus builds ribosomes. Proteins are made on ribosomes, free in the cytoplasm or on the rough ER.