Which organelle receives vesicles from the Rough ER and is the main site of protein modification and sorting before final destinations?

• A. Golgi apparatus
• B. Lysosome
• C. Peroxisome
• D. Mitochondrion

Answer: (A)

Proteins synthesized on the rough endoplasmic reticulum are carried in transport vesicles to the Golgi apparatus, which serves as the main processing and sorting center for these proteins. Inside the Golgi, proteins undergo post-translational modifications—such as glycosylation, and sometimes trimming, sulfation, or phosphorylation—and are then packaged into different vesicles based on their final destinations. The cis face receives the incoming vesicles, and the trans face, especially the trans-Golgi network, directs them to secretion outside the cell, incorporation into the plasma membrane, or delivery to lysosomes. This central role in modification and precise trafficking is what makes the Golgi apparatus the correct choice. The other organelles have different primary functions: lysosomes are degradative compartments; peroxisomes handle fatty acid breakdown and detoxification; mitochondria generate ATP and manage their own protein import, rather than acting as the main hub for secretory protein sorting.