Free and Bound Ribosomes? Cytosol?

- Two populations of ribosomes are evident in cells: free ribosomes (in the cytosol) and bound ribosomes (attached to the ER)​ - Free ribosomes mostly synthesize proteins that function in the cytosol ​ - Bound ribosomes make proteins of the endomembrane system and proteins that are secreted from the cell​. A majority of ribosomes are on the rough ER (bound ribosomes) - Ribosomes are identical and can switch from free to bound​ - Polypeptide synthesis always begins in the cytosol​ - Synthesis finishes in the cytosol unless the polypeptide signals the ribosome to attach to the ER​