Which of the following sequence represent a possible pathway in the production of a secretory protein ?

Options

A. Rough ER `rarr` Secretory vesicle `rarr` Ribosomes `rarr` Golgi apparatus
B. Ribosomes `rarr` Rough ER `rarr` Golgi apparatus`rarr` Secretory vesicle
C. Secretory vesicle `rarr` Golgi apparatus `rarr` Ribosomes `rarr` Rough ER
D. Rough ER `rarr` Ribosomes`rarr` Secretory vesicle `rarr` Golgi apparatus

Answer

To determine the correct sequence for the production of a secretory protein, we need to understand the pathway involved in protein synthesis and secretion. Here’s a step-by-step breakdown:

### Step 1: Ribosome
- **Explanation**: The process begins with ribosomes, which are the sites of protein synthesis. Ribosomes can be found free in the cytoplasm or bound to the rough endoplasmic reticulum (RER).
- **Hint**: Remember that ribosomes are often referred to as the "protein factories" of the cell.

### Step 2: Rough Endoplasmic Reticulum (RER)
- **Explanation**: Once the ribosome synthesizes the protein, it is typically associated with the rough endoplasmic reticulum. The RER has ribosomes on its surface, which is why it is termed "rough." The newly synthesized protein enters the lumen of the RER where it undergoes initial folding and modifications.
- **Hint**: Think of the RER as a processing center where proteins begin their journey.

### Step 3: Golgi Apparatus
- **Explanation**: After the RER, the protein is transported to the Golgi apparatus in vesicles. The Golgi apparatus further modifies, sorts, and packages the proteins for secretion or delivery to other destinations within the cell.
- **Hint**: The Golgi apparatus is often described as the "post office" of the cell because it modifies and sends proteins to their final destinations.

### Step 4: Secretory Vesicle
- **Explanation**: Once the proteins are processed in the Golgi apparatus, they are packaged into secretory vesicles. These vesicles then transport the proteins to the cell membrane for secretion outside the cell.
- **Hint**: Visualize secretory vesicles as delivery trucks that transport proteins to their final destination.

### Conclusion
The correct sequence for the production of a secretory protein is:
1. Ribosome
2. Rough Endoplasmic Reticulum (RER)
3. Golgi Apparatus
4. Secretory Vesicle

### Final Answer
The correct pathway is: **Ribosome → Rough Endoplasmic Reticulum → Golgi Apparatus → Secretory Vesicle.**