Golgi apparatus
/ GOAL-jee ap-uh-RAT-us /
After a product comes off the assembly line, it usually goes through a finishing-and-shipping department: stamping labels, adding final touches, and sorting items into the right delivery trucks. In the cell that department is the Golgi apparatus — a stack of flattened, curved sacs that receives proteins and lipids from the ER, modifies them, and dispatches them to their correct destinations.
The Golgi apparatus is a series of stacked membrane sacs (cisternae) with two faces: a receiving (cis) face near the ER and a shipping (trans) face pointing toward the cell surface. Vesicles arriving from the ER fuse with the receiving face; as their cargo moves through the stack toward the shipping face, enzymes trim and tag it — adding or editing sugar chains, attaching molecular address labels. At the far end, the finished cargo is repackaged into new vesicles addressed to lysosomes, the plasma membrane, or the outside world.
The Golgi is the central sorting hub of the endomembrane system: nearly everything the cell secretes or installs in its membranes passes through it. Its name honors Camillo Golgi, who first described it in 1898; for decades some doubted it was real rather than a staining artifact, but electron microscopy settled the question. It is especially prominent in cells that secrete a lot, such as mucus-producing or hormone-producing cells.
A goblet cell lining your gut sends raw mucus proteins from its ER to the Golgi, which adds heavy sugar coats to make them slippery before packaging them for release.
The Golgi adds the finishing chemistry that makes mucus mucus.
The Golgi does not make proteins — it modifies, sorts, and ships ones already built by ribosomes on the ER; mistaking it for a protein factory is a common error.