The sodium-potassium pump in animal cells requires cytoplasmic ATP to pump ions across the plasma membrane. When the proteins of the pump are first synthesized in the rough ER, what side of the ER membrane will the ATP binding site be on?
A)
It will be on the cytoplasmic side of the ER.
B)
It will be on the side facing the interior of the ER.
C)
It could be facing in either direction because the orientation of proteins is scrambled in the Golgi apparatus.
D)
It doesn't matter, because the pump is not active in the ER.
Answer: A