The Golgi apparatus functions in close association with the rough endoplasmic reticulum. When a protein is formed in the rough endoplasmic reticulum, the formation of transition vesicles takes place. This vesicle or sac floats via the cytoplasm to the Golgi apparatus and is then absorbed.
The vesicles transport the newly formed proteins to the Golgi apparatus. After the modification of the proteins is done by the Golgi apparatus, the vesicles transport the modified proteins to the membrane of the cell, where they are discharged.