Endomembrane System
The endomembrane system is the set of connected membrane-bound compartments inside a eukaryotic cell that make, modify, package and transport proteins and lipids.
The endomembrane system is the set of connected membrane-bound compartments inside a eukaryotic cell that make, modify, package and transport proteins and lipids. It includes the nuclear envelope, the endoplasmic reticulum, the Golgi apparatus, lysosomes and transport vesicles, and it connects to the plasma membrane.
The Secretory Pathway: How Does a Protein Travel?
Proteins destined for secretion are made on ribosomes attached to the rough endoplasmic reticulum and enter its interior as they are synthesized. They are folded, modified and packed into vesicles that bud off and fuse with the Golgi. There, sugars are added, the proteins are sorted, and new vesicles carry them to the cell surface, where they are released by exocytosis. George Palade's work on this pathway earned the 1974 Nobel Prize.
Degradation and Return: Where Do Things Go Back?
Material taken in by endocytosis is delivered to endosomes and then to lysosomes, whose enzymes break it down. Cells recycle membrane in this way and use it to remove worn-out parts. The smooth endoplasmic reticulum makes lipids and detoxifies chemicals, and it also supplies cell membrane components.
Evolution: Is It Found in Prokaryotes?
Bacteria do not have an endomembrane system, though some have internal membranes. Its appearance is considered a defining step in eukaryogenesis, and the nuclear envelope is continuous with the endoplasmic reticulum. Its parts are described in cell theory and architecture.
Endomembrane System at a Glance
| Property | Value |
|---|---|
| Parts | ER, Golgi, lysosomes, vesicles, nuclear envelope |
| Work recognized | George Palade, Nobel Prize 1974 |
| Absent from | Bacteria and archaea |
See Also
- Endoplasmic Reticulum — its largest compartment
- Golgi Apparatus — the sorting center
- Exocytosis — how contents leave the cell