Final answer:
Proteins travel through the Golgi apparatus via transport vesicles, which fuse with the cis face and release proteins for modification and sorting. After processing and tagging, proteins are repackaged into new vesicles at the trans face for delivery to their final destinations.
Step-by-step explanation:
Proteins travel from one cisterna to the next in the Golgi apparatus through the use of transport vesicles. These vesicles are formed in the rough endoplasmic reticulum (RER) and carry both packaged proteins and membrane proteins. When the vesicles reach the Golgi apparatus, they fuse with the cis face of the Golgi, releasing their contents into the lumen. As proteins and lipids move through the Golgi apparatus, they undergo various modifications, such as glycosylation - the addition of short sugar molecule chains. Subsequently, these modified molecules are tagged with phosphate groups or other small molecules, which act as signals for sorting to their final destinations. Eventually, the processed proteins are packaged into vesicles that bud off from the trans face of the Golgi apparatus. These vesicles then travel to and fuse with the plasma membrane or the membranes of other organelles, where the contents are utilized or secreted.