In the pulse-chase experiment discussed
in class, researchers applied a short pulse of radioactively labeled leucine, followed by a long chase of unlabeled leucine, to cells that secrete digestive enzymes. The bulk of the radioactive label was initially found in the rough ER, then in the Golgi apparatus, followed by secretory vesicles that emptied into a duct outside the cell. These results BEST support which of the following hypotheses?
Proteins that are destined to be secreted outside the cell follow a specific pathway that culminates with secretory vesicle fusion with the plasma membrane releasing the protein into the extracellular space.