Which of the following pathways is involved for packaging of secretory proteins?

Options

A. Trans face of Golgi body `to` Cis face of Golgi body `to` RER SER `to` Secretory vesicles
B. RER `to` Cis face of Golgi body `to` Trans face of Golgi body `to` Secretory vesicles
C. Cis face of Golgi body `to` Trans face of Golgi body `to` RER `to` Secretory vesicles
D. RER `to` Trans face of Golgi body `to` Cis face of Golgi body `to` Secretory vesicles

Answer

To determine the pathway involved in the packaging of secretory proteins, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Starting Point**: Secretory proteins are synthesized in the Rough Endoplasmic Reticulum (RER). The RER is studded with ribosomes, which are responsible for the translation of proteins.

2. **Movement to Golgi Apparatus**: After synthesis, these proteins are transported from the RER to the Golgi apparatus. The Golgi apparatus has two sides: the cis-phase (the receiving side) and the trans-phase (the shipping side).

3. **Entry into the Golgi Apparatus**: The secretory proteins first enter the Golgi apparatus at the cis-phase. This is where they are modified and sorted.

4. **Processing in the Golgi Apparatus**: Once in the Golgi apparatus, the proteins are processed and packaged. They move from the cis-phase to the trans-phase of the Golgi apparatus.

5. **Formation of Secretory Vesicles**: In the trans-phase, the proteins are packaged into secretory vesicles. These vesicles are larger than transport vesicles and are specifically designed for the secretion of proteins.

6. **Signal for Secretion**: The secretory vesicles wait for a signal (such as a hormonal or neural signal) to trigger their movement.

7. **Fusion with Plasma Membrane**: Upon receiving the signal, the secretory vesicles move towards the plasma membrane and fuse with it, releasing the secretory proteins outside the cell.

8. **Conclusion**: The correct pathway for the packaging of secretory proteins is from the Rough Endoplasmic Reticulum to the cis-phase of the Golgi apparatus, then to the trans-phase, and finally into secretory vesicles.

### Final Answer:
The correct option is: **Rough Endoplasmic Reticulum → Cis-phase of Golgi Apparatus → Trans-phase of Golgi Apparatus → Secretory Vesicles** (Option 2).

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