Which statement best describes the process of protein secretion in the endomembrane system?

• A. Proteins are synthesized in the cytoplasm and directly secreted through the plasma membrane.
• B. Proteins are synthesized in the rough endoplasmic reticulum, processed in the Golgi apparatus, and then transported in vesicles to the plasma membrane for secretion.
• C. Proteins are synthesized in the nucleus and transported directly to the plasma membrane for secretion.
• D. Proteins are synthesized in the smooth endoplasmic reticulum and secreted through lysosomes.

Answer: (B)

Verified step by step guidance

1. Understand that the endomembrane system is a group of membranes and organelles in eukaryotic cells that work together to modify, package, and transport lipids and proteins.
2. Recognize that protein synthesis begins in the rough endoplasmic reticulum (RER), where ribosomes are attached, giving it a 'rough' appearance. This is where proteins are synthesized and initially modified.
3. After synthesis in the RER, proteins are transported to the Golgi apparatus. Here, they undergo further modifications, such as glycosylation, which is the addition of sugar molecules.
4. Once processed, proteins are packaged into vesicles that bud off from the Golgi apparatus. These vesicles transport the proteins to their next destination.
5. Finally, the vesicles fuse with the plasma membrane, releasing the proteins outside the cell in a process known as exocytosis, completing the secretion process.