A cell frequently wants to secrete larger molecules than can be accommodated through the transport systems dealt with in Topic E3. Exocytoses get to the movement of proteins out of the cell across the plasma membrane into the extracellular space. The Proteins  intended  to  be  secreted  from  the  cell  are  interpreted   on  ribosome's attached to the RER. Membrane-bound vesicles having these proteins then bud off from the RER, migrate by the cytosol and fuse with the membrane of the Golgi apparatus that is given in the figure. On transport by the endoplasmic Golgi and reticulum    apparatus,   various    post- translational modifications to the proteins take place, like as glycosylation.

            figure:  Exocytosis of proteins by the constitutive and regulated secretory pathways.