Which statement correctly describes a function of the endomembrane system in protein secretion?

• A. Proteins are directly secreted from the nucleus to the plasma membrane without modification.
• B. The mitochondria are responsible for packaging and exporting secretory proteins.
• C. Lysosomes synthesize all proteins destined for secretion.
• D. Proteins synthesized in the rough endoplasmic reticulum are packaged into vesicles and transported to the Golgi apparatus for further modification.

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the role of the endomembrane system in protein secretion. The endomembrane system is a group of interconnected organelles that work together to synthesize, modify, package, and transport proteins and lipids within the cell.
2. Step 2: Recognize the function of the rough endoplasmic reticulum (RER). Proteins destined for secretion are synthesized by ribosomes attached to the RER. These proteins are inserted into the lumen of the RER for initial folding and modifications.
3. Step 3: Learn about vesicle transport. Once proteins are synthesized and modified in the RER, they are packaged into transport vesicles. These vesicles bud off from the RER and move toward the Golgi apparatus.
4. Step 4: Understand the role of the Golgi apparatus. The Golgi apparatus further modifies, sorts, and packages the proteins received from the RER. This includes adding carbohydrate groups (glycosylation) or other chemical modifications.
5. Step 5: Final transport and secretion. After processing in the Golgi apparatus, the proteins are packaged into secretory vesicles. These vesicles fuse with the plasma membrane, releasing the proteins outside the cell through exocytosis.