How Can Protein Molecules Be Positioned in the Plasma Membrane

Multiple Choice

How can protein molecules be positioned in the plasma membrane?

A) Protein molecules are buried in the lipid bilayer of the membrane and are not exposed to either the cytoplasm of the extracellular space.
B) All protein molecules completely span the membrane and face both the cytoplasm and the extracellular space.
C) Protein molecules can face only the extracellular side, only the cytoplasm, or span the membrane completely and face both the extracellular side and the cytoplasm.
D) Protein molecules in the membrane only face the cytoplasm.
E) Protein molecules in the membrane only face the extracellular space.