Final answer:
Proteins undergo stepwise modifications as they travel through the Golgi complex. They are modified, tagged, and packaged into secretory vesicles at different stages of the Golgi apparatus. These vesicles then deposit their contents within the cell or release them outside the cell.
Step-by-step explanation:
Proteins undergo stepwise modifications as they move along the Golgi complex. After leaving the endoplasmic reticulum (ER), transport vesicles fuse with the Golgi complex at the cis face and empty their contents into the Golgi apparatus' lumen. As the proteins and lipids travel through the Golgi, they undergo further modifications, such as the addition of short sugar molecule chains, and are tagged with phosphate groups or other small molecules. Finally, the modified and tagged proteins are packaged into secretory vesicles that bud from the trans face of the Golgi and are either deposited into other parts of the cell or fuse with the plasma membrane to release their contents outside the cell.