Question

structures of the cell quick check which of the following correctly shows the sequence of organelles a protein would take if it were being exported from the cell? (1 point) ○ ribosome → smooth er → vesicle → cell membrane → vesicle → rough er ○ ribosome → rough er → vesicle → golgi apparatus → vesicle → cell membrane ○ ribosome → vesicle → rough er → vesicle → golgi apparatus → cell membrane ○ smooth er → vesicle → golgi apparatus → rough er → vesicle → nucleus

Explanation:

To determine the correct sequence of organelles for a protein being exported from the cell, we recall the process of protein synthesis and secretion:

1. Ribosome: Proteins are synthesized here. For exported proteins, ribosomes attach to the Rough Endoplasmic Reticulum (Rough ER).
2. Rough ER: The protein is synthesized into the lumen of the Rough ER, where it undergoes initial processing.
3. Vesicle: The protein is then packaged into a vesicle that buds off from the Rough ER.
4. Golgi Apparatus: The vesicle fuses with the Golgi Apparatus, where the protein is further modified, sorted, and packaged.
5. Vesicle (from Golgi): A new vesicle buds off from the Golgi Apparatus, carrying the modified protein.
6. Cell Membrane: The vesicle fuses with the cell membrane, releasing the protein outside the cell.

Now let's analyze each option:

• First option: Smooth ER is not involved in the synthesis of exported proteins (Smooth ER is for lipid synthesis, detoxification, etc.), and the sequence is reversed at the end. Eliminate.
• Second option: Follows the correct sequence: Ribosome → Rough ER → Vesicle → Golgi Apparatus → Vesicle → Cell Membrane.
• Third option: The vesicle does not form before the Rough ER; the protein is synthesized on the Rough ER first, then packaged into a vesicle. Eliminate.
• Fourth option: Smooth ER is not the start, and the sequence (Smooth ER → Golgi → Rough ER → Nucleus) is incorrect for protein export. Eliminate.

Answer:

B. Ribosome → Rough ER → Vesicle → Golgi Apparatus → Vesicle → Cell Membrane