Final answer:
The Golgi apparatus utilizes the cis and trans faces for receiving and sending off proteins and lipids, where they are modified, tagged, and then packaged into vesicles. The old model of transport suggested vesicle-mediated movement across separate Golgi compartments, while the new cisternal maturation model suggests the compartments themselves mature and move towards the trans face.
Step-by-step explanation:
The Golgi apparatus plays a crucial role in the modification, sorting, and transport of proteins within the cell. The cis face is where transport vesicles from the rough endoplasmic reticulum (ER) fuse and release their protein and lipid contents into the lumen of the Golgi apparatus.
As these molecules traverse the Golgi compartments, they are modified, most frequently via the addition of sugar molecules. Then, they are tagged with various markers, such as phosphate groups, to ensure they reach their intended destinations within or outside the cell. Upon reaching the trans face, these modified proteins are packaged into secretory vesicles, with some contributing to internal cell processes and others fusing with the plasma membrane to excrete materials via exocytosis.
Historically, the vesicular transport model was the well-accepted explanation for movement through the Golgi, stipulating discrete vesicles shuttling cargo between Golgi cisternae.
The new model, often referred to as the cisternal maturation model, suggests that the cisternae of the Golgi apparatus mature as they move from the cis to the trans face, carrying the cargo with them, rather than the cargo moving via vesicles between stable Golgi compartments.