Figure 15-22 shows the organization of a protein that normally resides in the plasma membrane.The boxes labeled 1 and 2 represent membrane-spanning sequences and the arrow represents a site of action of signal peptidase.Given this diagram, which of the following statements must be TRUE? Figure 15-22

Question

Figure 15-22 shows the organization of a protein that normally resides in the plasma membrane.The boxes labeled 1 and 2 represent membrane-spanning sequences and the arrow represents a site of action of signal peptidase.Given this diagram, which of the following statements must be TRUE?  Figure 15-22

Quizplus · Accepted Answer

The protein has two membrane-spanning sequences, which suggests that it will cross the membrane twice. The arrow indicates that signal peptidase will cleave off the N-terminal signal sequence, which is typically on the luminal/extracellular side of the membrane. Thus, the N-terminus will not be cytoplasmic. Therefore, the C-terminus must be cytoplasmic. Option C is incorrect because it suggests that both termini are cytoplasmic, which doesn't make sense given the two membrane-spanning sequences.

Figure 15-22 Shows the Organization of a Protein That Normally