Golgi Apparatus @ Parthasarathy.M

Golgi

Apparatus

Golgi

Apparatus

Parthasarathy

IX-Roses

Golgi Apparatus @ Parthasarathy.M

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.

 

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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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