THE GOLGI APPARATUS, FINAL PROTEIN SORTER 
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n 1898, the Italian sci- 
entist Camillo Golgi, 
who had been studying 
stained owl and eat 
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 might 
he an artificial one, perhaps 
related to the stains that 
Golgi had used, he believed 
that the newly found 
organelle played a role in 
protein secretion. 
In the 1960’s, Palade and his 
colleagues confirmed Golgi’s 
theory by using radioactive 
labeling, staining, and elec- 
tron microscopy to follow 
proteins in pancreatic cells as 
they moved from the rough 
endoplasmic reticulum, 
through the Golgi apparatus, 
and into the secretory gran- 
ules that carried them out of 
the cell. 
It is now known that 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 
three distinct regions, and 
each sac in the organelle con- 
tains enzymes that modify 
proteins as they pass through. 
The sacs closest to the nucleus 
receive vesicles (membrane- 
hound sacs) filled with 
protein molecules from the 
endoplasmic reticulum. The 
proteins must pass through 
all the sacs in sequence to be 
processed correctly. 
