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INTRODUCTION
The Golgi apparatus (/ɡoʊldʒiː/), also known as the Golgi
complex, Golgi body, or simply the Golgi, is an organelle found in most
eukaryotic cells.It was identified in 1897 by the Italian physician Camillo
Golgi and named after him in 1898.
Part of the cellular endomembrane system, the Golgi apparatus packages
proteins into membrane-bound vesicles inside the cell before the vesicles
are sent to their destination.
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The Golgi apparatus resides at the intersection of the secretory, lysosomal, and
endocytic pathways. It is of particular importance in processing proteins for
secretion, containing a set of glycosylation enzymes that attach various sugar
monomers to proteins as the proteins move through the apparatus.
DISCOVERY Owing to its large size and distinctive structure, the Golgi apparatus was one of
the first organelles to be discovered and observed in detail. It was discovered in
1898 by Italian physician Camillo Golgi during an investigation of the
nervous system.
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GOLGI APPARATUSDiagram of a single "stack" of Golgi
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After first observing it under his microscope, he termed the structure theinternal reticular apparatus.
Some doubted the discovery at first, arguing that the appearance of the structure was merely an optical illusion created by the observation technique used by Golgi.
With the development of modern microscopes in the 20th century, the discovery was confirmed.
Early references to the Golgi referred to it by various names including the "Golgi–Holmgren apparatus", "Golgi–Holmgren ducts", and "Golgi–Kopsch apparatus".
The term "Golgi apparatus" was used in 1910 and first appeared in scientific literature in 1913.
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CAMILLO GOLGI
Camillo Golgi 7 July 1843 –21 January
1926) was an Italian physician,
biologist, pathologist, scientist, and
Nobel laureate. Several structures
and phenomena in anatomy and
physiology arenamed for him,
including the Golgi apparatus, the
Golgi tendon organ and the Golgi
tendon reflex.
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He is recognized as the greatest neuroscientist and biologist of his time.
Biography Camillo Golgi was born in July 1843 in the village of Corteno, in the province of
Brescia (Lombardy), Italy. The village is now named Corteno Golgi in his honour.
His father was a physician and district medical officer. Golgi studied at the
University of Pavia, where he worked in the experimental pathology laboratory
under Giulio Bizzozero, who elucidated the properties of bone marrow. He
graduated in 1865. He spent much of his career studying the central nervous
system.
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SUBCELLULAR LOCALIZATION
Among eukaryotes, the subcellular localization of the Golgi apparatus differs.
In mammals, a single Golgi apparatus complex is usually located near the
cell nucleus, close to the centrosome. Tubular connections are responsible
for linking the stacks together.
Localization and tubular connections of the Golgi apparatus are dependent on
microtubules. If microtubules are experimentally depolymerized, then the
Golgi apparatus loses connections and becomes individual stacks throughout
the cytoplasm.
Golgi Apparatus @ Parthasarathy.M
STRUCTURE
In most eukaryotes, the Golgi apparatus is made up of a series of
compartments consisting of two main networks: the cis Golgi network (CGN)
and the trans Golgi network (TGN). The CGN is a collection of fused, flattened
membrane-enclosed disks known as cisternae (singular: cisterna), originating
from vesicular clusters that bud off the endoplasmic reticulum.
A mammalian cell typically contains 40 to 100 stacks. Between four and eight
cisternae are usually present in a stack; however, in some protists as many
as sixty cisternae have been observed. This collection of cisternae is broken
down into cis, medial, and trans compartments.
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FUNCTION The Golgi apparatus is a major collection and dispatch station of protein
products received from the endoplasmic reticulum (ER). Proteins
synthesized in the ER are packaged into vesicles, which then fuse with the
Golgi apparatus. These cargo proteins are modified and destined for secretion
via exocytosis or for use in the cell.
In this respect, the Golgi can be thought of as similar to a post office: it
packages and labels items which it then sends to different parts of the cell or to
the extracellular space. The Golgi apparatus is also involved in lipid
transport and lysosome formation.
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The structure and function of the Golgi apparatus are intimately linked. Individual
stacks have different assortments of enzymes, allowing for progressive
processing of cargo proteins as they travel from the cis to the trans Golgi
face. Enzymatic reactions within the Golgi stacks occur exclusively near its
membrane surfaces, where enzymes are anchored.
This feature is in contrast to the ER, which has soluble proteins and enzymes in
its lumen. Much of the enzymatic processing is
post-translational modification of proteins. For example, phosphorylation of
oligosaccharides on lysosomal proteins occurs in the early CGN.
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VESICULAR TRANSPORT
The vesicles that leave the rough endoplasmic reticulum are transported to
the cis face of the Golgi apparatus, where they fuse with the Golgi membrane
and empty their contents into the lumen. Once inside the lumen, the molecules
are modified, then sorted for transport to their next destinations.
Those proteins destined for areas of the cell other than either the
endoplasmic reticulum or the Golgi apparatus are moved through the Golgi
cisternae towards the trans face, to a complex network of membranes and
associated vesicles known as the trans-Golgi network (TGN).
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BREFELDIN A
Brefeldin A (BFA) is a fungal metabolite used experimentally to disrupt
the secretion pathway as a method of testing Golgi function. BFA blocks
the activation of some ADP-ribosylation factors (ARFs).
ARFs are small GTPases which regulate vesicular trafficking through the
binding of COPs to endosomes and the Golgi. BFA inhibits the function of
several guanine nucleotide exchange factors (GEFs) that mediate GTP-
binding of ARFs.
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AN ANIMAL CELLComponents of a typical animal cell:1. Nucleolus
2. Nucleus
3. Ribosome (little dots)
4. Vesicle
5. Rough endoplasmic reticulum
6. Golgi apparatus (or "Golgi body")
7. Cytoskeleton
8. Smooth endoplasmic reticulum
9. Mitochondrion
10. Vacuole
11. Cytosol
12. Lysosome
13. Centrosome
14. Cell membrane
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