Episode 5 - The Golgi Body and Processing

The Golgi apparatus is composed many flattened disks of membrane, called Cisternae, which display polarity. The cis-face of the Golgi faces the ER, and receives protein/lipid vesicles from the ER. The trans-face of the Golgi faces the cell membrane, and secretes vesicles for use inside the rest of the cell, or for exocytosis out of the cell. Thus, the Golgi membranes are dynamic: the membranes are continually lost as vesicles on the trans side of the Golgi are being replaced by membranes constantly added to the cis-side of the Golgi from the ER.

Golgi Diagram. (Source: Encyclopedia Britannica Inc)

The Golgi apparatus plays a very important role in the cytomembrane system in Eukaryotic cells. The function of the Golgi body in this system is to take proteins and lipids from the ER and further modify them so that they are “complete” and functional; for instance, adding oligosaccharides onto ER proteins to turn them into fully functional glycoproteins. The Golgi also sorts the finished proteins/lipids according to molecular identification tags (like phosphate groups), packaging them into vesicles for transport to either specific organelles within the cell, or for secretion outside the cell. If the protein needs to be secreted, vesicles containing the protein bud off from the Golgi and fuses with the cell plasma membrane, whereupon the proteins are released via exocytosis. The Golgi also buds out other types of vesicles, including lysosomes (not peroxisomes)! But note that the Golgi does NOT work on proteins destined for the cytosol!

Micrograph of Golgi apparatus, visible as a stack of semicircular black rings near the bottom. Numerous circular vesicles can be seen in proximity to the organelle.  (Source: Wikimedia commons)

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