The cellular structure responsible for packaging proteins is known as the Golgi apparatus. The Golgi apparatus modifies, sorts, and packages proteins synthesized in the endoplasmic reticulum, preparing them for transport to their final destinations, such as secretion or use within the cell. It plays a critical role in the secretory pathway and is key for maintaining cellular function and integrity. Dysfunction of the Golgi can lead to various cellular disorders, emphasizing its importance in cell biology.