a) in a typical growing cell that is dividing once every 24 hours, the equivalent of one new plasma membrane must transit the ER every day. If the ER membrane is 40 times the area of plasma membrane, what is the ratio of plasma membrane proteins to other proteins in the ER? Assume that all proteins on their way to other compartments remain in the ER for 30 minutes on average before exiting, and that the ratio of proteins to lipids in the membranes of all compartments is the same.

b) if, in the same cell, the Golgi membrane is 8 times the area of the plasma membrane, what is the ratio of Golgi membrane proteins to other proteins in the ER?

c) If the membranes of all other compartments (lysosomes, endosomes, inner nuclear membrane, and secretory vesicles) that receive membrane proteins from the ER in total are 3 times the area of the plasma membrane, what fraction of the membrane proteins in the ER of this cell are permanent residents of the ER membrane?