The Golgi apparatus is part of the endomembrane system. It is responsible for modifying, packaging and transporting newly synthesized proteins and lipid molecules that it receives from the rough endoplasmic reticulum (rough ER) via transport vesicles. These vesicles arrive at the cis face of the Golgi, where they fuse with the membrane of the Golgi and empty their contents into the lumen. As these macromolecules pass from the cis to the trans poles of the Golgi apparatus, they are biochemically modified. Proteins undergo further glycosylation and lipids are metabolized. Once modified, proteins and lipids are sorted into transport vesicles that bud from the trans face of the Golgi and are transported to their targeted destination.