Which statement best defines an integral membrane protein?

• A. A protein permanently associated with the lipid bilayer that penetrates the hydrophobic core and typically requires detergents to be removed
• B. A protein that binds transiently to the membrane surface through ionic interactions and can be released by high salt or pH changes
• C. A soluble cytosolic protein that never associates with membranes and remains in the aqueous phase after cell fractionation
• D. A protein attached to the membrane only by a covalently linked carbohydrate chain on the extracellular surface

Answer: (A)