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 proteins are properly reoriented in the Golgi apparatus.
D) It doesn't matter, because the pump is not active in the ER.

Answer 1

The ATP binding site of the sodium-potassium pump will be on the cytoplasmic side of the ER membrane after synthesis, ensuring accessibility to ATP in the cytosol when the protein reaches the plasma membrane.

Step-by-step explanation:

The sodium-potassium pump is a transmembrane protein that requires an ATP binding site to function. When proteins of the pump are synthesized in the rough Endoplasmic Reticulum (ER), the ATP binding site will be on the cytoplasmic side of the ER membrane. This orientation ensures that ATP, which is present in the cytosol, can readily bind to the site when the protein is later embedded in the plasma membrane.