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STRUCTURE AND FUNCTIONS OF GOLGI APPARATUS (GOLGI BODY)

Published in Cell Biology
Wednesday, 07 June 2017 07:17
In the animal and plant cells clus­ters of fat filled structures are present. They are called Golgi apparatus or complex. In 1898 Camillo Golgi' recognised it in the nerve cell of the owl. The Golgi complex of invertebrates is called dictyo­some.
 
Occurence: Golgi complex is seen in all eukaryotic cells. Golgi complex is not seen in mature sperm, red blood cell and prokaryotes.
 
Golgi complex occurs in two forms
 
a) Localized form: Golgi complex occurs singly and has a fixed position. (In between nucleus and secretory pore)
 
b) Diffused form: In the nerve and liver cells Golgi complex is scattered, in it each unit is called dictyosome.
 
Structure: Golgi body is seen in the form of three components.
 
1. Cisternae: These are tubular, flat, fluid filled sacs. They show 200 to 300A0 width. Each sac is covered by two membranes. In a dictyosome 3 to 7 cisterne are present. They are arranged one above the other. Their convex side is towards nucleus and their concave surface is towards plasma membrane. The convex side of the cisternae is called forming face. The concave surface is called maturing face. It shows big secreting vesicles. These secretory vesicles store secretory substances. They may develop into lysosomes.
 
Polarity of cisternae: The cisternae shows maturing face and forming face. Forming face is convex and towards nucleus. The smooth E.R. gives vesicles. They unite to form cisternae.
 
2. Golgi vesicles: On the forming face of golgi cisternae small vesicles are present. They are 400 A° width. They usually develop form E.R.
 
3. Secretory vesicles: On the maturing face of golgi cisternae secretory vesicles are present. They contain secretory products of golgi. They finally change into lysosomes.

Chemical Composition:
 
Golgi complex will be rich in chemical substances.
 
  1. Phospholipids: These substances have a composition which is in between the structure of phospholipids of endoplasmic reticulum and plasma membrane.
  2. Enzymes: ATP-ase, CPT-ase, transphorases, etc. enzymes are. present.
  3. Carbohydrates: Glucose, manose, galactose carbohydrates are seen.
 
Origin of Golgi Complex:
 
  1. From E R: Beams & Kessel' in 1968 proposed that Golgi system cisternae arise from Endoplasmic reticulum.
  2. Rough E.R. produces protein which will be transfer to smooth ER.
  3. Vesicles are developed from smooth E.R.
  4. By the fusion of vesicles cisternae are formed. From the cisternae secretory vesicles are formed on the maturing face. (These sides are called "G.E.R.L" -  Golgi Endoplasmic Reticulum Lysosome)
 
golgi apparatus 27

2) From nuclear membrane: In 1965 "Bouch" described the origin of golgi from the outer membrane of the nucleus. Vesicles are pinched off from the outer nuclear membrane and they are united to form cistemae.
 
3) By the division pre-existing dictyosome: During the cell division the number of dictyosomes will increase. In each daughter cell the number of dictyosomes will be equal to the dictyosome of parent cell.
 
4) Zones of exclusion: Each golgi complex is surrounded by a specific zone of cytoplasm. In this zone ribosomes and other organelles are absent. Such zone is called "Exclusive zone". E. R. present in this zone will show smooth surface.
 
Functions: Golgi complex is mainly connected with secretory function. In different types of cells different types of secretions are produced.
 
Golgi complex & secretion: The secretory mechanism will follow
 
  1. Proteins are produced by ribosome.
  2. They will be transmitted to smooth E.R.
  3. From there they are concentrated at Golgi complex.
  4. From the Golgi complex the secretory vesicles are formed.
 
They produce the secretion. The secretions are three types.
 
a) Holocrine secretion: The entire cell is filled with secretory product, it gives rise to secretions. Ex: Sebaceous gland.
b) Apocrine secretion: The secretory vesicles will come out of the plasma membrane. They take away small amount of cytoplasm. Ex: Apocrine sweat gland.
c) Merocrine secretion: Secretory vesicles will unit with P.M. and open to the exterior. Ex: Salivary gland.
 
S.No. ' Cell type -------- Golgi function
 
1. Pancreas ------- Digestive enzymes
2. Haepatic cells of liver ------ Secretion of lipids
3. Plasma cells of blood ------ Immunoglobulins
4. Thyroid gland ------ Thyroxin
 
2) Synthesis of glycoprotein: Most of the cells will produce glycopro­teins. The glycoprotein contains a protein part and carbohydrate part. They are important for secretions.
 
3) Storage of secretory products: Ribosome synthesize proteins, they are discharged into E.R. They are concentrated in the cistemae. They are stored in secretory vesicles. Thus the glycoproteins are stored in Golgi.
 
4) Formation of lysosomes: From the maturing face of cistemae granules are produced. They are united to form lysosomes.
 
5) Acrosome formation: "Burgos" stated that acrosome of the sperm is formed because of golgi spermatogensis golgi complex will develop into each vacuole a small proacrosomal granule is formed. If spherical body. Inside each vacuoleIt increases in size and they are many, they unite to form a single granule, acrosomal granule is formed It forms the acrosome. Acrosome is helps penetrate into ovum during fertilization.

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