Final answer:
The soluble proteins of the protein coat assemble on the cytosolic surface of the donor membrane, and clathrin and COP proteins help in vesicle budding from the trans Golgi stack. Peripheral membrane proteins synthesized inside the ER lumen end up on the plasma membrane's exterior surface.
Step-by-step explanation:
The protein coat contains soluble proteins that assemble on the cytosolic surface of the donor membrane at sites where budding takes place. The cargo proteins are selected and packaged into vesicles that bud off from the trans Golgi stack. These vesicles acquire coat proteins, such as clathrin and COP proteins, which help shape the vesicle and select cargo proteins for transport. Once the vesicle buds off, it navigates to its target destination where the process of vesicle fusion occurs, mediated by V-SNARE and T-SNARE proteins.
For example, a peripheral membrane protein synthesized in the lumen of the endoplasmic reticulum (ER) would end up on the outside of the plasma membrane once the vesicle containing this protein fuses with the cell membrane. This is because the inside of the ER lumen and the vesicle that buds from it corresponds to the outside of the cell once the vesicle has fused with the plasma membrane.