Question

A researcher is studying the movement of a protein that is secreted from a eukaryotic cell. Which pathways best represents the movement she could expect for packaging/processing of the secretory protein?

Answer 1

The researcher studying the movement of a secretory protein in a eukaryotic cell would expect a pathway that involves the synthesis in the endoplasmic reticulum, processing in the Golgi apparatus, and ultimately exocytosis at the cell membrane.

The movement of a secretory protein in a eukaryotic cell typically involves the endomembrane system and various cellular organelles. The secretory pathway, also known as the exocytic pathway, describes the process by which proteins are synthesized, modified, and transported to the cell membrane for secretion. Here is an overview of the main steps in the secretory pathway:

Synthesis of the Protein:

The secretory protein is initially synthesized on ribosomes bound to the endoplasmic reticulum (ER).

Processing and Modification in the Endoplasmic Reticulum (ER):

The protein undergoes post-translational modifications and folding in the ER.

Transport to the Golgi Apparatus:

Transport vesicles carry the protein from the ER to the Golgi apparatus.

Processing in the Golgi Apparatus:

Within the Golgi apparatus, the protein undergoes further processing, including glycosylation and sorting.

Sorting and Packaging into Vesicles:

The processed protein is sorted into vesicles for transport to the cell membrane.

Transport to the Cell Membrane:

Vesicles containing the secretory protein move towards the cell membrane along microtubules using motor proteins.

Exocytosis:

The vesicle fuses with the cell membrane, releasing the secretory protein into the extracellular space.

The pathways involved in the secretory pathway are interconnected and involve different organelles, including the endoplasmic reticulum, Golgi apparatus, and vesicles.

Answer 2

The secretory protein is synthesized in the RER, then transported to the Golgi apparatus for modification and packaging. Finally, it is transported in secretory vesicles that fuse with the plasma membrane to release the protein outside the cell, a process known as exocytosis.

Step-by-step explanation:

To understand the movement of a protein that is secreted from a eukaryotic cell, it is essential to consider the protein's journey through the cell's secretory pathway. Initially, the synthesis of the protein begins in the rough endoplasmic reticulum (RER), where secretory proteins are formed and threaded into the cisternae. After this, the vesicle containing the newly synthesized protein buds from the RER and travels to the Golgi apparatus. In the Golgi, the protein is modified, tagged, and then packaged into vesicles that bud from the Golgi's trans face. Two pathways may occur at this point:

• Some vesicles may become transport vesicles, which deposit their contents within other parts of the cell.
• Other vesicles become secretory vesicles, which fuse with the plasma membrane and release their contents outside the cell in a process known as exocytosis.

Consistently, the correct pathway that describes the movement of a secretory protein for packaging and processing would be option b.