Endomembrane system

The endomembrane system is a network of eukaryotic-cell membranes and organelles that synthesizes, modifies, transports, and recycles proteins and lipids.

Endoplasmic reticulum: A membrane network that synthesizes proteins and lipids, folds proteins, and contributes to intracellular transport. Its rough and smooth regions begin much of the system’s protein and lipid production.
Vesicle: A small membrane-enclosed compartment that transports or stores substances within or outside a cell. Vesicles connect separated organelles without merging their membranes permanently.
Secretory pathway: The route by which proteins and lipids move from the endoplasmic reticulum through the Golgi apparatus to cellular destinations. It describes the system’s forward flow from synthesis to secretion or membrane delivery.
Mitochondrion: A double-membraned organelle that produces much of a eukaryotic cell’s ATP through oxidative phosphorylation. Unlike endomembrane compartments, mitochondria are not considered part of the system.
N-linked glycosylation: The attachment of an oligosaccharide to the nitrogen atom of asparagine in a protein. It begins in the endoplasmic reticulum and supports protein folding and quality control.
Golgi apparatus: A stack of membrane-bound compartments that modifies, sorts, and packages proteins and lipids. It receives much newly made cargo and directs it toward cellular destinations.
Membrane trafficking: The movement of membrane and cargo among cellular compartments through budding, transport, docking, and fusion. It is the traffic process that links the system’s membrane-bound compartments.
Exocytosis: The release of cellular substances when an intracellular vesicle fuses with the plasma membrane. Secretory vesicles use this process to deliver cargo outside the cell.
Chloroplast: A photosynthetic organelle in plants and algae that converts light energy into chemical energy. Its membranes form an organelle system distinct from endomembrane trafficking.
Unfolded protein response: A cellular stress response that adjusts gene expression and protein synthesis when unfolded proteins accumulate in the endoplasmic reticulum. It helps the system cope when its protein-folding capacity is exceeded.

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