How does the Golgi Apparatus modify biomolecules?

The Modification Process:

1. Vesicles containing proteins made in the ER move from the ER to Golgi body
2. Vesicles coalesce to form new cis Golgi cisternae (a vesicle that buds from the ER can add its membrane and contents of its lumen to the cis face by fusing with a Golgi Membrane)
3. Cisternal maturation occurs: Golgi cisternae move in a cis-to-trans direction. As the cisternae move, they encounter different enzymes that are responsible for modifying the structure of the proteins and lipids
4. Vesicles form and leave Golgi, carrying specific proteins to other locations or to plasma membrane for secretion
5. Vesicles transport some proteins backward to less mature Golgi cisternae, where they function

One example of modification of biomolecules by the Golgi Apparatus includes:

Glycosylation, the process in which various Golgi enzymes modify the carbohydrate portions of glycoproteins. The steps of glycoslyation are

1. Carbohydrates first added to proteins in rough ER, during process of polypeptide synthesis
2. the carbohydrate on resulting glycoprotein is then modified as it passes through rest of ER and Golgi
3. Golgi removes some sugar monomers and substitutes others, producing a large variety of carbohydrates.

Final Shipping Process:

Before a Golgi stack sends its products via vesicles that have budded from the ‘trans’ face, it sorts these products and targets them for various parts of the cell. Different enzymes add “molecular identification tags” such as phosphate groups to Golgi products, that aid in sorting much like zip codes on mailing labels. In addition, transport vesicles that have budded from Golgi may have external molecules on their membranes that recognize “docking sites” on the surface of specific organelles or on the plasma membrane

Important Note: many macromolecules are manufactured by Golgi itself. For example, polysaccharides such as pectin are Golgi products.