Final answer:
Receptor proteins for mitochondria are located on the outer mitochondrial membrane. Peripheral membrane proteins synthesized in the ER lumen are transported to the outside of the plasma membrane. The ER lumen correlates with the extracellular environment upon exocytosis.
Step-by-step explanation:
The question pertains to the location of receptor proteins related to mitochondria and the eventual placement of peripheral membrane proteins synthesized in the endoplasmic reticulum (ER). The structure of a mitochondrion includes both an outer and an inner mitochondrial membrane. Receptor proteins that guide mitochondrial proteins into the mitochondria are located on the outer mitochondrial membrane. These proteins accept the mitochondrial protein from the cytoplasm, which usually exposes an N-terminal signal peptide that is recognized by the receptor protein on the outer mitochondrial membrane.
If a peripheral membrane protein is synthesized within the ER lumen, it would eventually end up on the outside of the plasma membrane because proteins are translocated into the ER during synthesis and then transported to the cell surface by vesicles, a process called exocytosis. Thus, the inside of the ER corresponds to the outside of the cell and the cellular plasma membrane.