NLN NEX Science Practice Test

The presence of ribosomes on the surface and the role in handling newly made proteins point to the rough endoplasmic reticulum. Its ribosomes give it a “rough” appearance and they are the sites where proteins destined for secretion, insertion into membranes, or delivery to lysosomes are synthesized. After production, these proteins enter the ER lumen, where they’re folded and stored briefly, and then packaged into vesicles that bud off to be transported to the Golgi apparatus for further processing and sorting. The rough ER’s combination of ribosome-studded surface and protein packaging/transport function distinguishes it from the other organelles: the lysosome focuses on digestion, the Golgi modifies and ships proteins but doesn’t have ribosomes on its surface, and the smooth ER lacks ribosomes and specializes in lipid synthesis and detoxification.