Endosomes are the containers cells use to transport materials for use within a cell or disposal. Endosomes exemplify the tidiness and intelligence which cells have.
An endosome is a membrane-bound bag (vesicle) inside a eukaryotic cell. Many endosomes are constructed and packed in a Golgi complex: a packaging and transport hub organelle in most eukaryotic cells.
Organelles are workspaces within cells. Organelles are tidily enclosed by membranes. Each organelle membrane has a troop of proteins to monitor and manage the spherical border. Using the membrane as a permeable barrier, proteins on an organelle regulate what comes in or goes out of it.
The Golgi body is a stack of membranes that works in concert with an endoplasmic reticulum (ER) to package proteins and other materials before shipping them to their intended destination. Enzymes trains newly synthesized proteins in the Golgi to improve their job performance potential. An ER is a manufacturing facility for a cell, as well a manager which helps maintain cell health. Cells may have many Golgi bodies and ERs.
Cells synthesize a sizable number of protein-based macromolecules. Some are used internally (endocytosis). Others are secreted for use by other cells (exocytosis).
Materials coming into a cell from outside are packaged into endosomes on the cell surface for transport within the cell. Debris within cells is also put into endosomes for recycling or disposal. “Endosomal transport is essential for cellular organization and compartmentalization and cell–cell communication,” notes German cytologist and biochemist Anne Sprang.
Proteins inside an endosome process and sort the contents. This is a team effort requiring considerable skill. Chemical compounds and molecules which can be reused are separated from bits to be disposed of.
Endosome transport is also complex task. Proteins on an endosome drive and attach to certain cellular structures to pick up, distribute, or dispose of endosomal contents accordingly. “Coordination drives cargo at endosomes into recycling pathways,” reports Sprang.
Ishi Nobu, The Science of Existence, BookBaby (2019).
Jachen A. Solinger et al, “FERARI is required for Rab11-dependent endocytic recycling,” Nature Cell Biology (27 January 2020).
“How cells sort and recycle their components,” ScienceDaily (27 January 2020).
Mark Alliegro, “Endocytosis,” in xPharm: The Comprehensive Pharmacology Reference, Elsevier (2007).