Final answer:
Deleting the cytoplasmic regions of an integral membrane protein likely increases its mobility in the membrane due to reduced interactions with cytoskeletal elements. Peripheral membrane proteins synthesized in the ER lumen end up outside of the cell after processing. Orientation and traffic along the endomembrane pathway dictate the final position of membrane proteins.
Step-by-step explanation:
When the DNA sequence for an integral membrane protein is modified to delete the cytoplasmic portions of the protein and inserted into cells, the protein's mobility in the membrane is likely to increase. This is because the interaction of the cytoskeletal elements like actin with the cytoplasmic regions of integral membrane proteins often serves to anchor these proteins, creating microcompartments within the membrane that restrict their movement. This anchoring mechanism, part of the Fences and Pickets model, results in the immobilization of the protein within certain areas of the membrane. Cytochrome c, as a peripheral protein, isn't anchored and thus can dissociate easily from the membrane, illustrating the distinction from integral membrane proteins.
If a peripheral membrane protein were synthesized inside the lumen of the endoplasmic reticulum (ER), it would end up on the outside of the plasma membrane after being processed through the endomembrane system, which includes the ER and Golgi apparatus. This system ensures that luminal proteins remain on the same side of the membrane, which becomes the exterior of the cell once exocytosis occurs.
Furthermore, the N-terminal end of a plasma membrane polypeptide typically ends up exposed to the outside of the cell, indicating the orientation of transmembrane proteins during their insertion and subsequent exocytotic transport to the plasma membrane. Hence, traffic on the endomembrane highway and the ultimate destination of membrane proteins are intricately linked to how they are inserted and sorted during synthesis within the cell.