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:

A) protein was not translated by the ribosomes.

B) protein does not possess a signal peptide for localization within the lumen of the rough endoplasmic reticulum.

C) protein possesses a signal for localization within the Golgi apparatus.

D) all of the above

C) protein possesses a signal for localization within the Golgi apparatus.

Explanation:

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.