Golgi Apparatus or Golgi body | NEET BIOLOGY

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CELL : STRUCTURE AND FUNCTIONS

Golgi Apparatus or Golgi body

• Golgi Apparatus or Golgi Complex Golgi complex it is also called as Golgi Apparatus, Dalton Complex, Apparato Reticulare, is a complex cytoplasmic structure made up of smooth membrane saccules or cisternae, a network of tubules with vesicles and vacuoles, which takes part in membrane transformation , secretion and production of complex biochemicals.
• It is surrounded by an organelle free cytoplasm called zone of exclusion or Golgi ground substance.
• It was first seen by George (1867) but is named after Italian scientist Camillo Golgi, who in 1898 recognised the apparatus as reticular structure (apparato reticulare) near the nucleus. 
• In the nerve cells of barn owl and cat by means of metallic impregnation method. 
• Its structure was studied under electron microscope by Dalton and Felix (1954 ). 

Occurrence 

• Golgi apparatus or complex is absent in prokaryotic cells (PPLO , bacteria and blue - green algae).
• It is present in all eukaryotic cells except sieve tubes of plants, sperms of bryophytes and pteridophytes and red blood corpuscles of mammals. 

Location 

• In animal cells Golgi complex or apparatus is either single or consists of a single connected complex.
• The two conditions are respectively called localised (most ver tebrate cells) and diffused (most invertebrate cells, liver and nerve cells of vertebrates). 
• The localised organelle is compact.
• It generally occurs at one end between the nucleus and the periphery.
• The diffused organelle is found to form a network, e.g. , around the nucleus in nerve cells. 
• In plant cells, Golgi apparatus is formed of a number of unconnected units called dictyosomes. 
• Their number is highly variable from one in certain simple algae to 25000 in rhizoidal cell of Chara. 
• Commonly there are 10–20 dictyosomes per plant cell. 
• A liver cell may possess upto 50 units of Golgi apparatus called Golgisomes.

Structure 

• The shape and size of Golgi complex are not fixed. 
• They depend upon the physiological state of the cells. 
• A typical plant dictyosome is 0.5-1.0 um in diameter. 
• Usually Golgi complex is made up of four parts cisternae, tubules, vesicles and vacuoles.

Cisternae 

• Golgi complex consists of a stack of generally 4–8 ( range 3-20 ) membrane bound saccules or cisternae.
• Unicisternal dictyosomes are found in fungi.
• The membranes of the saccules or cisternae are smooth but of variable thickness.
• They enclose a lumen of 60-90 Å.
•  Lumen contains a fluid substance or matrix.
• In a stack , thea djacent cisternae are separated by a distance of 100-300 Å.
• The intercisternal space con tains thin layer of cytoplasm having parallel fibrils.
• The saccules are frequently curved to give a definite polarity to the Golgi apparatus.
• One face of the apparatus is convex while the other is concave.
• The convex side is called forming (= formative, cis - face ) face while the concave side of the apparatus is known as maturing face ( trans - face ). 
• The membranes of the maturing face are 7-8 nm in thickness while those of the forming face are about 4 nm in thickness.
• The forming face receives (transitional) vesicles from endoplasmic reticulum. 
• Their contents pass through various cisternae with the help of coated vesicles and intercisternal connectives.
• They ultimately reach the maturing face where they are budded off as secretion, coated or Golgian vesicles or vacuoles.
• While passing through the apparatus, biochemicals are variously transformed.

Tubules 

• They form a complicated network towards the periphery and maturing face of the apparatus.
• Actually tubules arise due to fenestrations of the cisternae.
• They have a diameter of 30-50 nm.
• The tubules interconnect the different cisternae.

Vesicles 

• They are small sacs of 20-80 nm diameter.
• The vesicles are found attached to the tips of tubules at various levels in the network.
• They are of two types, smooth and coated.
• The coated vesicles have a rough surface.
• They elaborate membrane proteins.
• The smooth vesicles have a smooth surface.
• They contain secretory substances and are hence known as secretion vesicles.

Golgian Vacuoles 

• They are expanded parts of the cisternae which have become modi fied to form vacuoles.
• The vacuoles develop from the concave or maturing face Golgian vacuoles contain amorphous or granular substance.
• Some of the golgian vacuales function

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