The primary function of the Golgi apparatus is to modify, package and transport newly synthesized proteins and lipid molecules that it receives from the rough ER. Vesicles transport these materials from the rough ER to the cis face of the Golgi stack. The membrane of the vesicle fuses with that of the Golgi and the vesicle’s contents are emptied into the lumen of the Golgi. In the lumen, enzymes biochemically modify the newly synthesized proteins and lipids (e.g. protein glycosylation and lipid metabolism). Processed proteins and lipids are then passed through the trans region of the Golgi to the trans Golgi network for packaging and vesicle transport to areas within or outside the cell.