An electron micrograph of a pancreatic secretory cell shows two endoplasmic reticulum regions, one turning out exported digestive enzymes and one building lipids. Which feature marks the protein-exporting region?

Core Concept

Rough ER earns its texture from bound ribosomes actively translating secretory proteins into the lumen. Pancreatic digestive enzymes follow this route, entering the endomembrane system for folding, modification, and eventual release. Smooth regions lack ribosomes and specialize in lipid synthesis and detoxification instead.