The Golgi complex or Golgi apparatus is responsible for manufacturing, warehousing, and shipping certain cellular products, particularly those from the endoplasmic reticulum (ER). Depending on the type of cell, there can be just a few complexes or there can be hundreds. Cells that specialize in secreting various substances typically have a high number of Golgi complexes.
Golgi Complex: Distinguishing CharacteristicsA Golgi complex is composed of flat sacs known as cisternae. The sacs are stacked in a bent, semicircular shape. Each stacked grouping has a membrane that separates its insides from the cell's cytoplasm. Golgi membrane protein interactions are responsible for its unique shape. These interactions generate the force that shapes this organelle. The Golgi complex is very polar. Membranes at one end of the stack differ in both composition and in thickness from those at the other end. One end (cis face) acts as the "receiving" department while the other (trans face) acts as the "shipping" department. The cis face is closely associated with the ER.
Golgi Complex: Molecule Transport and ModificationMolecules synthesized in the ER exit via special transport vesicles which carry their contents to the Golgi complex. The vesicles fuse with Golgi cisternae releasing their contents into the internal portion of membrane. The molecules are modified as they are transported between cisternae layers. It is thought that individual sacs are not directly connected, thus the molecules move between cisternae through a sequence of budding, vesicle formation, and fusion with the next Golgi sac. Once the molecules reach the trans face of the Golgi, vesicles are formed to "ship" materials to other sites.
The Golgi complex modifies many products from the ER including proteins and phospholipids. The complex also manufactures certain biological polymers of its own. The Golgi complex contains processing enzymes which alter molecules by adding or removing carbohydrate subunits. Once modifications have been made and molecules have been sorted, they are secreted from the Golgi via transport vesicles to their intended destinations. Some of the molecules are destined for the cell membrane where they aid in membrane repair and intercellular signaling. Other molecules are secreted to areas outside of the cell. Transport vesicles carrying these molecules fuse with the cell membrane releasing the molecules to the exterior of the cell. Still other vesicles contain enzymes that digest cellular components. These vesicle form cell structures called lysosomes. Molecules dispatched from the Golgi may also be reprocessed by the Golgi.