5.9: Golgi Apparatus

Properly folded and assembled proteins are selectively packaged into vesicles that exit the ER. Motor proteins transport these vesicles to the Golgi apparatus for adding modifications that make these proteins functional at their destination.

The Golgi apparatus is a eukaryotic organelle that has a distinctive ribbon-like appearance. It is a primary sorting and dispatch station for cargo arriving from the ER. Newly arriving vesicles enter the cis face of the Golgi, closest to the ER, and are transported through a stack of membrane-enclosed cisternae. Each cisterna contains unique compositions of enzymes and performs specific protein modifications, such as phosphorylation and glycosylation. After modifications in the trans cisterna, proteins are given tags that define their cellular destination.

Depending on the molecular tags, proteins are packaged into vesicles and trafficked to particular cellular locations, such as the plasma membrane. Specific markers on the membranes of these vesicles allow them to dock at the appropriate cellular location.

In the eukaryotic cell, next to the ER, is the Golgi apparatus, a stack of disc-shaped membrane-bound compartments called cisternae with two distinct faces, cis and trans.

Each cisterna contains unique enzymes and trafficking proteins that process proteins and lipids as they move through the Golgi.

Proteins and lipids from the ER enter the cis-Golgi and then move through the medial cisternae, where they are chemically modified by adding sugars, phosphates, or sulfates.

These modifications make proteins functional at their target organelle. Farthest from the ER is the trans-Golgi network, where the molecules are sorted according to their final destination, which can be the cell membrane, lysosomes, or the extracellular matrix.

During sorting, each molecule is tagged with a signal sequence that will be recognized by a receptor on its destination organelle.

Finally, the cargo molecules are packaged in transport vesicles and dispatched to their destinations within the cell.