Golgi Apparatus
"The golgi apparatus sorts and packages proteins"
Flattened stacks of membranes, often interconnected with one
another, form a complex called the Golgi body.
These structures
are named for Camillo Golgi , the 19th-century physician who first
identified them. The number of stacked membranes within the Golgi body ranges from 1 or a few, in protists, to 20 or more in
animal cells and to several hundred in plant cells. They are
especially abundant in glandular cells, which manufacture and
secrete substances. The Golgi body is often referred to as the
Golgi apparatus (see figure).The Golgi apparatus is a
smooth, concave, membranous structure. It receives material for
processing in transport vesicles on the cis face and sends the
material packaged in transport or secretory vesicles off the trans face . The substance in a vesicle could be for export out of the cell
or for distribution to another region within the same cell.
smooth, concave, membranous structure. It receives material for
processing in transport vesicles on the cis face and sends the
material packaged in transport or secretory vesicles off the trans face . The substance in a vesicle could be for export out of the cell
or for distribution to another region within the same cell.
The Golgi apparatus is the post office of the cell. It functions
in the collection, packaging, and distribution of molecules synthesized at one location and used at another within the cell or even
outside of it. A Golgi apparatus has a front and a back, with distinctly different membrane compositions at these opposite ends.
The front, or receiving end, is called the cis face and is usually
located near ER. Materials arrive at the cis face in transport vesicles that bud off the ER and exit the trans face , where they are
discharged in secretory vesicles (see figure).
Figure:Protein transport through the endomembrane
system. Proteins synthesized by ribosomes on the RER are
translocated into the internal compartment of the ER. These
proteins may be used at a distant location within the cell or
secreted from the cell. They are transported within vesicles that
bud off the rough ER. These transport vesicles travel to the cis
face of the Golgi apparatus. There they can be modified and
packaged into vesicles that bud off the trans face of the Golgi
apparatus. Vesicles leaving the trans face transport proteins to
other locations in the cell, or they fuse with the plasma membrane,
releasing their contents to the extracellular environment.
How material transits through the Golgi apparatus has been a source of much contention. Models include maturation of the individual cisternae
from cis to trans, transport between cisternae by vesicles, and
direct tubular connections. Although there is probably transport of
material by all of these, it now appears that the primary mechanism is cisternal maturation.
Proteins and lipids manufactured on the rough and smooth
ER membranes are transported into the Golgi apparatus and modified as they pass through it. The most common alteration is the
addition or modification of short sugar chains, forming glycoproteins and glycolipids. In many instances, enzymes in the Golgi
apparatus modify existing glycoproteins and glycolipids made in
the ER by cleaving a sugar from a chain or by modifying one or
more of the sugars. These are then packaged into small,membrane-bounded vesicles that pinch off from the trans face of
the Golgi apparatus. These vesicles then diffuse to other locations
in the cell, distributing the newly synthesized molecules to their
appropriate destinations.
Another function of the Golgi apparatus is the synthesis of
cell-wall components. Noncellulose polysaccharides that form
part of the cell wall of plants are synthesized in the Golgi apparatus and sent to the plasma membrane, where they can be added to
the cellulose that is assembled on the exterior of the cell. Other
polysaccharides secreted by plants are also synthesized in the
Golgi apparatus.
in the collection, packaging, and distribution of molecules synthesized at one location and used at another within the cell or even
outside of it. A Golgi apparatus has a front and a back, with distinctly different membrane compositions at these opposite ends.
The front, or receiving end, is called the cis face and is usually
located near ER. Materials arrive at the cis face in transport vesicles that bud off the ER and exit the trans face , where they are
discharged in secretory vesicles (see figure).
system. Proteins synthesized by ribosomes on the RER are
translocated into the internal compartment of the ER. These
proteins may be used at a distant location within the cell or
secreted from the cell. They are transported within vesicles that
bud off the rough ER. These transport vesicles travel to the cis
face of the Golgi apparatus. There they can be modified and
packaged into vesicles that bud off the trans face of the Golgi
apparatus. Vesicles leaving the trans face transport proteins to
other locations in the cell, or they fuse with the plasma membrane,
releasing their contents to the extracellular environment.
How material transits through the Golgi apparatus has been a source of much contention. Models include maturation of the individual cisternae
from cis to trans, transport between cisternae by vesicles, and
direct tubular connections. Although there is probably transport of
material by all of these, it now appears that the primary mechanism is cisternal maturation.
Proteins and lipids manufactured on the rough and smooth
ER membranes are transported into the Golgi apparatus and modified as they pass through it. The most common alteration is the
addition or modification of short sugar chains, forming glycoproteins and glycolipids. In many instances, enzymes in the Golgi
apparatus modify existing glycoproteins and glycolipids made in
the ER by cleaving a sugar from a chain or by modifying one or
more of the sugars. These are then packaged into small,membrane-bounded vesicles that pinch off from the trans face of
the Golgi apparatus. These vesicles then diffuse to other locations
in the cell, distributing the newly synthesized molecules to their
appropriate destinations.
Another function of the Golgi apparatus is the synthesis of
cell-wall components. Noncellulose polysaccharides that form
part of the cell wall of plants are synthesized in the Golgi apparatus and sent to the plasma membrane, where they can be added to
the cellulose that is assembled on the exterior of the cell. Other
polysaccharides secreted by plants are also synthesized in the
Golgi apparatus.
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