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. Proteins are synthesized at ribosomes. Ribosomes attached to the Rough Endoplasmic Reticulum (Rough ER) synthesize proteins that are to be exported or inserted into membranes.
2. The newly synthesized protein enters the Rough ER, where it is folded and modified.
3. From the Rough ER, the protein is packaged into a vesicle. This vesicle transports the protein to the Golgi Apparatus.
4. In the Golgi Apparatus, the protein undergoes further modifications (such as glycosylation) and is sorted for transport.
5. The Golgi Apparatus then packages the protein into another vesicle.
6. This vesicle transports the protein to the cell membrane, where the protein is released outside the cell (exocytosis).

Now let's analyze each option:

• First option: The sequence is incorrect as it involves Smooth ER (which is not involved in protein synthesis for export in this way) and has a wrong order (e.g., Cell Membrane before Golgi and Rough ER at the end).
• Second option: Follows the correct pathway: Ribosome (synthesis) → Rough ER (modification) → Vesicle (transport to Golgi) → Golgi Apparatus (further modification and sorting) → Vesicle (transport to cell membrane) → Cell Membrane (secretion).
• Third option: The order of Vesicle before Rough ER is incorrect. Proteins go to Rough ER first after ribosome, not into a vesicle directly.
• Fourth option: Starts with Smooth ER (incorrect, as protein synthesis for export starts at ribosomes on Rough ER) and has a wrong sequence (e.g., Golgi before Rough ER, and ending at Nucleus which is not part of the secretion pathway).

Answer:

B. Ribosome → Rough ER → Vesicle → Golgi Apparatus → Vesicle → Cell Membrane (assuming the second option is labeled as B; if the original options had different labels, adjust accordingly. Based on the given options, the correct one is the second option: Ribosome → Rough ER → Vesicle → Golgi Apparatus → Vesicle → Cell Membrane)