They are sandwiched between two layers of heads. Recall that the heads are hydrophilic therefore they will always be on the outside and the tails are hydrophobi therefore they willl always be away from water, there fore sandwiched. I'm a bio major, hope I helped :)
Answer:
Pumps, also called transporters, are transmembrane proteins that actively move ions and/or solutes against a concentration or electrochemical gradient across biological membranes. One moves with the concentration gradient (high to low) which powers the movement of the other against the gradient (low to high).
Your answer is D. Nucleotide
