Question

A radioactively labeled protein is made by cells and followed through the various organelles in the secretory pathway. After six hours, all of the radioactivity is still primarily in the Golgi apparatus. This suggests that the _____

Answer 1

This suggests that the protein is targeted to Golgi apparatus.

Protein targeting or sorting is a process by which synthesized proteins are transported to their appropriate localizations in the cell or outside it. Proteins can be targeted to the inner space of an organelle (such as Golgi apparatus or endoplasmic reticulum) or its membrane, plasma membrane, or to exterior of the cell via secretion.  

Usually, protein contains signal sequence on the N terminus that is involved in destination targeting.