Which statement about peripheral proteins is true?

• A. They span the entire thickness of the membrane
• B. They are embedded within the lipid bilayer
• C. They are located on the outer surface of the membrane
• D. They are located on the inner surface of the membrane

Answer: (D)

Peripheral proteins are attached to the membrane surface rather than spanning the bilayer. They don’t cross the membrane; instead they associate loosely with the phospholipid heads or with integral proteins, typically on the cytoplasmic (inner) face of the membrane. This inner-side location allows them to interact with the cytoskeleton and signaling machinery inside the cell. That’s why the statement describing them as located on the inner surface is the best general description. Spanning the membrane or being embedded in the bilayer refers to integral or transmembrane proteins, while being on the outer surface is not the defining feature of peripheral proteins.