Question

If the pinsulin receptor, a, example of an integral membrane protein, is cotranslationally inserted into the ER membrane with the N-terminus on the cytosolic side of the membrane and the C-terminus in the lumen of the ER, which side of the protein would you expect to bind to the ligand, pinsulin, when the protein is found on the cell surface?
(A) N-terminal end of the protein will bind pinsulin
(B) Neither will bind to a ligand because both ends of the protein will be extracellular and will compete with each other
(C) C-terminal end of the protein will bind pinsulin
(D) Neither will bind to a ligand because both ends of the protein will be cytoplasmic

Answer 1

Answer:

The correct answer is option C.

Explanation:

As the proteins are produced in the endoplasmic reticulum membrane, they amalgamate with the vesicles and then they are conducted towards the membrane's cell surface where they act as an integral membrane protein.  

The outer end will bind with the ligand and the other one will get attached towards the cytoplasm. Thus, the pinsulin in the given case will combine with the C terminus of the protein.