Which organelle is primarily responsible for modifying and sorting proteins for secretion?

• A. Endoplasmic Reticulum
• B. Ribosome
• C. Golgi apparatus
• D. Lysosome

Answer: (C)

Proteins destined for secretion are processed in stages, with the Golgi apparatus serving as the central processing and sorting station. Proteins are synthesized and folded in the rough endoplasmic reticulum, where initial modifications occur, then packaged into vesicles and delivered to the Golgi. In the Golgi, they undergo further processing, such as glycosylation, and receive address tags that direct them to their final destinations. The Golgi then sorts and packages these proteins into secretory vesicles that move to and fuse with the plasma membrane to release their cargo outside the cell. Other organelles have different roles: ribosomes build the proteins, the endoplasmic reticulum handles folding and initial modifications, and lysosomes digest materials. Because this is where refinement and routing toward secretion happen, the Golgi apparatus is primarily responsible for modifying and sorting proteins for secretion.