Protein Trafficking (Golgi) -- Movie Narrative
It is important that translated proteins are delivered to their specific cellular location. To accomplish this, the protein is transferred through a series of membrane structures. A principle membrane component is the Golgi apparatus.
The Golgi apparatus is the sorting organelle of the cell. Proteins from the rough endoplasmic reticulum are sent to the Golgi. As the proteins move through the Golgi apparatus, they are modified and packaged into vesicles. Because the Golgi apparatus receives proteins from one location and targets them for delivery to a second location, it is sometimes considered the “Post Office” of the cell.
The Golgi apparatus consists of general components: the cis cisterna nearest the endoplasmic reticulum or ER, the medial and trans cisternae, and the trans Golgi network.
Other key players in this process are the proteins being transported and the enzymes that modify them.
Translated proteins are encapsulated in vesicles in the ER. A group of these vesicles fuse, and these fused vesicles form the cis-cisterna. As the protein moves through the stack, it is modified by RESIDENT Golgi enzymes at specific locations in the apparatus. These modifications are important because they provide the signal that determines the final destination of the protein.
So how does the protein move through the Golgi? Movement occurs in waves. First the cis-cisterna becomes part of the medial Golgi cisternae. Behind it, a new cis-cisterna is formed by the fusion of vesicles from the endoplasmic reticulum. Meanwhile, one of the medial cisternae migrates and becomes the new trans-cisterna. Collectively, this process is known as the cis-maturation model.
Proteins are sorted within the trans Golgi network. Proteins with the same target sequence and are destined for delivery to the same location.
The trans Golgi network then buds off into vesicles. These vesicles then migrate to their target location. These locations include internal organelles such the lysosome, the digestive organelle of the cell. The vesicles can also be targeted to the cell membrane where the targeted protein can be released from the cell for delivery elsewhere in the organism.