<P> In addition to making secretory proteins, the rough ER makes membranes that grows in place from the addition of proteins and phospholipids . As polypeptides intended to be membrane proteins grow from the ribosomes, they are inserted into the ER membrane itself and are kept there by their hydrophobic portions . The rough ER also produces its own membrane phospholipids; enzymes built into the ER membrane assemble phospholipids . The ER membrane expands and can be transferred by transport vesicles to other components of the endomembrane system . </P> <P> The Golgi apparatus (also known as the Golgi body and the Golgi complex) is composed of separate sacs called cisternae . Its shape is similar to a stack of pancakes . The number of these stacks varies with the specific function of the cell . The Golgi apparatus is used by the cell for further protein modification . The section of the Golgi apparatus that receives the vesicles from the ER is known as the cis face, and is usually near the ER . The opposite end of the Golgi apparatus is called the trans face, this is where the modified compounds leave . The trans face is usually facing the plasma membrane, which is where most of the substances the Golgi apparatus modifies are sent . </P> <P> Vesicles sent off by the ER containing proteins are further altered at the Golgi apparatus and then prepared for secretion from the cell or transport to other parts of the cell . Various things can happen to the proteins on their journey through the enzyme covered space of the Golgi apparatus . The modification and synthesis of the carbohydrate portions of glycoproteins is common in protein processing . The Golgi apparatus removes and substitutes sugar monomers, producing a large variety of oligosaccharides . In addition to modifying proteins, the Golgi also manufactures macromolecules itself . In plant cells, the Golgi produces pectins and other polysaccharides needed by the plant structure . </P> <P> Once the modification process is completed, the Golgi apparatus sorts the products of its processing and sends them to various parts of the cell . Molecular identification labels or tags are added by the Golgi enzymes to help with this . After everything is organized, the Golgi apparatus sends off its products by budding vesicles from its trans face . </P>

Endomembrane route through which a protein is secreted from a cell