Which feature defines the rough endoplasmic reticulum?

• A. It lacks ribosomes
• B. It detoxifies drugs
• C. It is continuous with the Golgi apparatus
• D. Fixed ribosomes give rough appearance

Answer: (D)

The feature that defines the rough endoplasmic reticulum is the presence of ribosomes fixed on its cytosolic surface, giving it a rough, studded appearance. Those attached ribosomes drive protein synthesis for secreted, membrane, and lysosomal proteins and feed nascent polypeptides into the ER lumen or membrane as they are made. This region is part of the ER network that is continuous with the outer membrane of the nucleus, and proteins produced here are later transported in vesicles to the Golgi for further processing. In contrast, which lacks ribosomes and forms smooth ER, handles lipid synthesis and detoxification, so detoxification isn’t a defining feature of the rough type. The Golgi is fed by vesicles from the ER rather than being a direct, physical continuation of the ER itself.