Final answer:
Proteins in the cytosol destined for other endomembrane compartments must enter the endoplasmic reticulum (ER). The endomembrane system processes and transports proteins and lipids, with the ER playing a crucial role in protein synthesis.
Step-by-step explanation:
The proteins in the cytosol that are destined for other endomembrane compartments must first enter the endoplasmic reticulum (ER). The endomembrane system, which includes the ER, Golgi apparatus, and other cellular components, works together to modify, package, tag, and transport proteins and lipids. In the ER, ribosomes use RNA to create different types of proteins needed by the body.