Final answer:
The secretory pathway involves the synthesis, modification, sorting, and transport of proteins to their final destinations, including secretion outside the cell. It includes steps from the synthesis in the rough ER, modification in the Golgi apparatus, packing into vesicles, and release through exocytosis. Some cells have regulated pathways for secretion in response to specific stimuli.
Step-by-step explanation:
The secretory pathway is a critical cellular process through which proteins are synthesized, modified, sorted, and transported to their final destinations, including secretion outside the cell. The key steps in this pathway include:
- Synthesis of proteins on bound ribosomes within the rough endoplasmic reticulum (RER).
- The emerging proteins enter the RER lumen where they begin to fold and undergo initial modifications.
- Proteins are then transported from the RER to the Golgi apparatus in transport vesicles.
- Within the Golgi apparatus, proteins undergo further modifications and are sorted for their final destination.
- Modified and tagged proteins are packaged into secretory vesicles that bud from the Golgi's trans face.
- Some vesicles deliver their contents to other parts of the cell, while others fuse with the plasma membrane to release their contents outside of the cell, a process known as exocytosis.
In addition to constitutive secretion, cells can have regulated secretory pathways where substances are stored in vesicles and released in response to specific signals. An example of regulated secretion is the release of histamine by immune cells upon encountering a pathogen.