THE GOLGI APPARATUS, 
FINAL PROTEIN SORTER 
In 1 898, the Italian scientist Camillo 
Golgi, who had been studying stained 
owl and cat nerve cells under his light 
microscope, saw a cell structure that 
did not look like the nucleus. Although 
some biologists at the time thought the 
structure was just an artifact — perhaps 
related to the stains Golgi had used — 
Golgi believed the newly found organ- 
elle played a role in protein secretion. 
In the 1960's, Palade and his col- 
leagues confirmed Golgi's theory by 
using radioactive labeling, staining, 
and electron microscopy to follow 
proteins in pancreatic cells as they 
moved from the rough endoplasmic 
reticulum, through the Golgi apparatus, 
and into the secretory granules that 
carried them out of the cell. Although 
the details are still unclear, it is now 
known that the Golgi apparatus plays 
an important role in transforming many 
newly made proteins into mature, 
functional ones by "labeling" them with 
chemical tags and "shipping" them to 
their destinations. 
Each Golgi apparatus consists of 
a stack of flat, membranous sacs that 
are piled one on top of the other like 
dinner plates. The stack is composed 
of at least three chemically distinct 
regions, and each sac in the organelle 
contains enzymes that modify proteins 
as they pass through. The sacs closest 
to the nucleus receive vesicles filled 
with protein molecules from the endo- 
plasmic reticulum. The proteins must 
pass through all the sacs in sequence 
to be processed correctly. 
Why does the cell go to such 
elaborate lengths to modify and sort 
proteins? According to James Rothman 
of Princeton University, the compart- 
mental organization of the Golgi 
apparatus is "crucial to the functioning 
of the cell, because without it thou- 
sands of enzymes would be randomly 
mixed, resulting in a chaotic splay of 
biochemical activity." The Golgi 
apparatus controls the chaos by pack- 
aging proteins into vesicles as they 
pass through the organelle. The 
protein-filled vesicles then migrate to 
another organelle or to the cell's 
surface, where they fuse with the cell's 
outer membrane and release their 
contents. This is how cells secrete 
hormones, enzymes, and other types 
of proteins as needed. 
Inside the Golgi apparatus, proteins 
are modified depending upon their 
ultimate destinations. For example, 
proteins bound for the cell's surface 
membrane are modified in one way, 
while proteins that will eventually 
move to the cell's "digestive" organ- 
elles undergo a different series of 
changes. 
