Sodium Potassium Pump AP Bio Question?

Question

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.

e. Not enough information is provided to answer this question.

Answer 1

It's A.  Once integral membrane proteins are synthesized in the ER their cytoplasmic face is always cytoplasmic.  The exception is when the protein is being shuttled into a MVB for it's eventual degradation in lysosomes.