Answer: Secretory proteins are directed to the rough ER.
- A Nuclear proteins enter the nucleus through pores
- B Secretory proteins are directed to the rough ER
- C Mitochondrial proteins are imported through TOM complexes
- D All organelle proteins are targeted using one universal signal
Correct answer: B. Secretory proteins are directed to the rough ER
Explanation: Blobel's signal hypothesis: N-terminal signal sequence on secretory proteins directs ribosomes to rough ER; protein enters the ER lumen.
Animal cell structure with major organelles labeled. Image: LadyofHats (Mariana Ruiz), Public Domain, via Wikimedia Commons.
Concept context
Cell theory, prokaryotic vs eukaryotic cells, organelles and their functions. Foundation of all biology.