EXOCYTOSIS
1) Proteins synthesized in the endoplasmic reticulum and trafficked to the Golgi apparatus
2) From the Golgi, the proteins are sorted and can follow different paths:
3a) Constitutive secretory pathway
- Also called default pathway as it does not require a signal for cargo to enter this pathway
- Can transport soluble proteins or plasma membrane proteins
- Transport vesicles fuse with the plasma membrane and release their contents (plasma membrane proteins become accessible to the extracellular space)
- Found mainly in specialized cells that release molecules like hormones, neurotransmitters, etc.
- Secretory vesicles are blocked from fusing with the plasma membrane without a proper signal
- An extracellular ligand binds a cellular receptor which causes an intracellular signal that releases the block on the secretory vesicles
- Secretory vesicles then fuse with the plasma membrane and release their cargo