Considering the following hydropathy plot for a multipass transmembrane protein in the plasma membrane, are the protein termini expected to be located inside (I) or outside (O) of the cell? Which of the regions indicated as 2 and 3 in the plot is expected to have more positively charged residues? The position of positively charged residues near the first transmembrane helix is indicated by an asterisk on the plot.
A) I; 2
B) I; 3
C) O; 2
D) O; 3

Question

Considering the following hydropathy plot for a multipass transmembrane protein in the plasma membrane, are the protein termini expected to be located inside (I) or outside (O) of the cell? Which of the regions indicated as 2 and 3 in the plot is expected to have more positively charged residues? The position of positively charged residues near the first transmembrane helix is indicated by an asterisk on the plot. 
A) I; 2 
B) I; 3 
C) O; 2 
D) O; 3

Quizplus · Accepted Answer

The N-terminal position of positively charged residues around the first helix suggests that it will be oriented with this terminus facing inside. This therefore places loop 2 in the cell interior as well, which would be consistent with this loop bearing a larger positive charge than the extracellular loops 3 and 1 (not indicated).

Considering the Following Hydropathy Plot for a Multipass Transmembrane Protein