Question

describe the correct pathway for a protein that is destined to be secreted from the cell. ribosome on rough er -> golgi apparatus -> vesicle -> cell membrane; nucleus -> golgi apparatus -> rough er -> cell membrane; free ribosome -> cytoplasm -> cell membrane; smooth er -> lysosome -> cell membrane

Explanation:

To determine the correct pathway for a secreted protein, we recall the secretory pathway: Proteins for secretion are synthesized by ribosomes on the rough endoplasmic reticulum (RER). Then they move to the Golgi apparatus for processing, are packaged into vesicles, and the vesicles fuse with the cell membrane to release the protein.

• The blue option is incorrect as the nucleus is not part of the protein - secretion pathway, and the order (nucleus -> Golgi -> Rough ER) is wrong.
• The orange option is incorrect because free ribosomes synthesize proteins for use within the cell (cytoplasmic proteins), not secreted proteins.
• The cyan option is incorrect as the smooth ER is not involved in the synthesis of secreted proteins, and lysosomes are for intracellular digestion, not secretion.
• The green option follows the correct secretory pathway: Ribosome on Rough ER (synthesis) -> Golgi Apparatus (processing) -> Vesicle (transport) -> Cell Membrane (secretion).

Answer:

A. Ribosome on Rough ER -> Golgi Apparatus -> Vesicle -> Cell Membrane