What does the rough ER do?

• A. Detoxifies chemicals
• B. Packages proteins
• C. The rough ER helps produce proteins.
• D. Stores energy

Answer: (C)

The rough endoplasmic reticulum is studded with ribosomes, which makes it the site where new proteins are synthesized. As ribosomes build polypeptide chains, these chains are threaded into the ER lumen or inserted into the ER membrane, guided by signal sequences. Inside the ER, the proteins begin to fold and may receive initial modifications with help from chaperone proteins. Once properly folded, they’re packed into transport vesicles that bud from the ER and carry the proteins to the Golgi apparatus for further processing and sorting to their final destinations, such as secretion, incorporation into membranes, or lysosomes. Detoxification is mainly a job of the smooth ER, and storing energy is handled by mitochondria (and chloroplasts in plants), so those roles don’t fit the rough ER’s function. Therefore, describing it as helping produce proteins is the best answer.