Final answer:
Upon membrane integration, the C-terminus or N-terminus location for each protein is predicted as NCC for the single-pass protein, CNC for the protein that crosses three times, and CNN for a second protein that crosses three times, based on whether the number of passes is even or odd and the orientation of termini during synthesis.
Step-by-step explanation:
The C-terminus or N-terminus location of each protein after membrane integration is predicted as follows: NCC, CNC, CNN. In general terms, the orientation of a transmembrane protein's termini after integration into the membrane depends on the topology and number of times the protein spans the membrane. Considering that the N-terminal end of a transmembrane protein typically faces the extracellular side upon integration, and given the fact that proteins are synthesized from N-terminus to C-terminus, we can infer their cytosolic orientation based on the manner in which they span the membrane. For example, a protein that crosses the membrane an even number of times will have its C-terminus exposed to the cytosol, whereas an odd number of crossings would result in the N-terminus facing the cytosol.
This is based on the knowledge that membrane proteins with an N-terminal signal sequence are synthesized beginning with the N-terminus in the cytosol but are anchored in the membrane by stop-transfer sequences. These sequences halt translocation across the membrane, leaving the remainder of the protein to loop out either into the cytosol or the extracellular space. Therefore, a single-pass protein like CCC will have its N-terminus outside the cell, making the correct answer NCC, not the CCC indicated in the question. A protein like CNC that crosses the membrane three times will have its C-terminus in the cytosol, the correct answer being CNC. Finally, for NNC, since it crosses the membrane three times, its N-terminus will be in the cytosol, making the correct answer CNN.