You make radioactively labeled ribosomal subunits and you microinject them to cells which you are culturing in the laboratory. At different times after you inject the subunits, you take a small amount of cells and analyze them by electron microscopy. You find out very soon after injection, the labeled subunits are assembled to cytosolic ribosomes. As more time passes, labeled subunits can be seen in both cytosolic and ER-bound ribosome. Interpret such observations.