What organelle is primarily involved in processing and packaging secretory proteins?

The Golgi body, also known as the Golgi apparatus, plays a crucial role in the processing and packaging of secretory proteins. This organelle functions as a central hub for modifying proteins that have been synthesized in the rough endoplasmic reticulum. Once these proteins reach the Golgi apparatus, they undergo further modifications, such as glycosylation, which adds carbohydrate groups, and sorting, where they are directed to their final destinations, such as secretion outside the cell or delivery to other organelles.

The Golgi body organizes these proteins into vesicles, which can then bud off and transport the modified proteins either to the cell membrane for secretion or to specific organelles. This process is essential for the proper functioning of cells that rely on secretory proteins for various purposes, such as hormones, enzymes, and other signaling molecules.

In contrast, other organelles mentioned do not perform this specific function. Mitochondria are involved in energy production; the rough endoplasmic reticulum is primarily responsible for the synthesis of proteins but not their final processing and packaging; while lysosomes are involved in the degradation of waste materials and cellular debris, rather than the packaging of proteins for secretion.