Versicular transport from the rER to the Golgi apparatus
a. Transport vesicles containing newly synthesized proteins pinch off the smooth surfaced
regions of the rER. These regions are called transitional elements of the rER
b. The vesicles move to and fuse with membranes of the cis Golgi
Versicular transport to other membranous organelles
Proteins that begin their synthesis in the rER move from the rER to the Golgi apparatus, move between
and among Golgi stacks, and move from the trans-Golgi network to their final destinations by way of
vesicles. The vesicles pinch off from one membrane, move to the next membranous compartment
(target) in the pathways, fuse with it and deliver their content. They then pinch off from the target
membrane and return to and fuse with the original membrane to pick up more cargo.
Golgi Apparatus
Morphology
The Golgi apparatus is an organelle that appears as a stack of 6-8 plate like membranous compartments
associated vesicles and vacuoles, often located near the centrosome (Figure 2-3)
1. Vesicles. Large numbers of small vesicles are associated with the Golgi stacks. They are
clustered on the cis face of the Golgi apparatus, which is the side nearest the rER. Vesicles are
responsible for the directed movement of molecules from the rER to the Golgi apparatus.
a. Vesicles are also arrayed along the outer rims of the Golgi cisternae
b. These small vesicles are responsible for the directed movement of molecules between the
sub compartments of the Golgi apparatus.
2. Vacuoles. Vacuoles are located on the trans face of the Golgi apparatus, which is the side
furthest away from the rER. vacuoles are responsible for concentration and transport if finished
products to their final destinations
3. Functional Compartments of the Golgi Apparatus. The Golgi apparatus can be separated into
four functionally distinct compartments: cis Golgi stacks, medial Golgi stacks, trans Golgi
stacks, and the trans Golgi network (TGN). The first three are involved in post translational
modification of molecules transisting the stacks. The TGN is involved in sorting the molecules
to their final destination (i.e. to lusosomes, to secretory vesicles or to the plasma membrane)
Function. The Golgi apparastus functions in the further modificiation of proteins and lipids sunthesixed
in the ER
1. Processing of N linked oligosaccharide chains. N linked oligosaccharide synthesized in the rER
are further processed in the Golgi apparatus in the cis and nmedial Golgi stacks.
2. Syntheiss of O-linked glycoproteins. The addition of sugars to proteins at serine residues (Olinked glycoproteins) is accomplished in the medial and trans Golgi stacks by integral
membrane proteins called glycosyltransferases. These enxymes also add sugars to the serine
residues of glycolipids in the Golgi stacks.
3. Processing of acid hydrolases. Acid hydrolases destined for lyssosomes are synthesized by
polysomes of the rER. Further processing in the cis Golgi stacks targets them to the lysosomes.