Consider a protein that is made in the rough endoplasmic reticulum. You observe that when the synthesis of the protein is completed, the protein is located in the ER membrane. Where else in the cell might this protein be found?

• A. In the aqueous interior of a lysosome, functioning as a digestive enzyme
• B. In the cytoplasm, functioning as an enzyme in carbohydrate synthesis
• C. In the internal space of the Golgi apparatus, being modified before the protein is excreted
• D. In a mitochondrion, functioning in ATP synthesis
• E. Embedded in the plasma membrane, functioning in the transport of molecules into the cell