Here's a breakdown:
* Ribosomes are the protein synthesis factories of the cell. They read the genetic code from messenger RNA (mRNA) and use that information to assemble amino acids into proteins.
* Proteins destined for export have a special signal sequence that tells the ribosome to attach to the endoplasmic reticulum (ER).
* The ER is a network of membranes that acts as a sort of "highway" for proteins being exported. The ribosomes attached to the ER continue to synthesize the protein, and as it's made, it gets threaded into the ER lumen (the space inside the ER).
* From the ER, the protein might travel to the Golgi apparatus for further processing and packaging before being exported from the cell.
So, while the ribosome is the site of protein synthesis, the entire process of exporting proteins involves several structures within the cell working together.
