GOLGI COMPLEX

GOLGI COMPLEX / GOLGI APPARATUS:-
    
       Golgicomplex is a complex cytoplasmic structure made up of smooth membrane saccules or Cisternae,a network of tubule with vesicles and vacuoles ,which takes part in membrane transfermation, secretion and production of complex biochemicals. It is sorrounded by an organelle free cytoplasm called zone of exclusion or golgi ground substances.

  Occurance:- Golgi apparatus or complex is absent in prokaryotic cell. It is present in all eukaryotic cells except sieve tubes of plants ,sperms of bryophyte and pteridophytes and red blood corpuscles of mammals.

 Location:- In animalcell Golgi complex is either single or consists of a single connected complex. The two condition are respectively called localised and diffused . The localised organelle is compact. It generally occurs at one end between the nucleus and the periphery . The diffused organelle is found to from a network , e.g., around the nucleus in nerve cells.

STRUCTURE OF GOLGI COMPLEX:-

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

1) CISTERNAE:- Golgi complex consists of a stack of generally 4-8 membrane bound saccules or Cisternae . The membrane of the sacules  are smooth but of variable thickness . They enclose a lumen of 60-90 Armstrong .Lumen contains a fluid substance or matrix . The sacules are frequently curved to give a definite polarity to the Golgi apparatus .one face of the apparatus is concave and another one is convex. The convex side is called Forming face and the concave side is called maturing face. 

2) Tubules:- they form a complicated network towards the periphery and maturing face of the apparatus . Actually tubules arise due to fenestration of the cistarnae . They have a diameter of 30-50 nm. The Tubules interconnect the different Cisternae.

3)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 vessicles have a smooth surface .they contain secretory substances and are hence knwon as secretion Vesicles .

4)Golgian vacuoles :-  They are expanded parts of the Cisternae which have become modified to form vacuoles. The vacuoles develop from the concave or maturing face. Golgian vacuoles contain amorphous or granular substance .Some of the Golgian vacuoles function as lysosomes.

                                      

FUNCTION OF GOLGI COMPLEX:-

  

 1) Secretion:- All glandular cells depend upon Golgi complex for concentrating and packaging their products inside a soluble protein coat visible as dark staining under electron microscope. They are sent out of the cells through "exocytosis".

2) Glycoproteins and Glycolipids:- proteins synthesised by the rough Endoplasmic reticulum and lipids synthesised from smooth Endoplasmic reticulum reach the cistarnae of the Golgi apparatus. Here, they combine with carbohydrates to form Glycolipids and Glycoproteins.

3) Hormones:-  production of hormones by endocrine gland is mediated through it.

4) Synthesis of pigments :-  In chick embryo the retinal pigment has been observed to be synthesised by Golgi complex

5) Formation of acrosome:-  Acrosome is an important constituent of the tip of animal sperms which help in digesting away the covering sheath of the egg or ovum during fertilization. It is synthesised by Golgi complex with the help of its vessicles.

6) Formation of Lysosomes:- Some of the vesicles or vacuoles of the Golgi apparatus store digestive enzymes obtained through ER In the inactive state. They act as primary Lysosomes.