Final answer:
Secretory proteins in eukaryotic cells start their journey in the rough endoplasmic reticulum, where they are synthesized and may undergo initial modifications. They're then transported to the Golgi apparatus for further modification and sorting. Finally, they are packed into vesicles that fuse with the plasma membrane to release the proteins outside the cell or become part of the cell membrane.
Step-by-step explanation:
Secretory proteins in eukaryotic cells follow a specific pathway from synthesis to secretion. This process begins with protein synthesis on bound ribosomes of the rough endoplasmic reticulum (RER). Proteins are deposited into the RER lumen, where they may undergo initial modifications such as folding or addition of side chains.
From the RER, proteins travel in vesicles to the Golgi apparatus, entering through the cis Golgi cisternae. They pass through the medial Golgi cisternae, where further glycosylation and modification occur. Finally, proteins reach the trans Golgi cisternae, where they are sorted and packed into vesicles. These vesicles then move to the plasma membrane, where they either become integral membrane proteins or release their contents outside the cell through exocytosis.
It's important to note that not all vesicles directly fuse with the plasma membrane. Some vesicles deposit their contents within different parts of the cell, such as lysosomes or peroxisomes, depending on the protein's ultimate function. However, for secretory proteins, the final step typically involves fusion with the plasma membrane and secretion out of the cell.