5. Cell Structure And Organization - part 07 - Golgi complex

 

5. Cell Structure And Organization - part 07 - Golgi complex

Golgi complex / Golgi apparatus / Golgi body:

• It is  manufacturing cum packaging and transport unit of cell.
• Golgi complex essentially consists of stacks of membranous sacs called cisternae.
• Diameter of cisternae varies from 0.5 to 1 μm. 
• A cell may have few to several cisternae depending on its function.
• The thickness and molecular composition of two membranes of a Golgi sac differ from each other. 
• The Golgi sacs show specific orientation in the cell. 
• Each cisterna has a forming or ‘cis’ face (cis: on the same side) and maturing or ‘ trans’ face (trans: the opposite side).
• Transport vesicles that pinch off from transitional ER merge with cis face of Golgi cisterna and add its contents into the lumen.
• This explains why Golgi bodies are usually located near ER. 
• Modified and condensed secretions leave Golgi through trans face again as membrane bound vesicles.
  
• Golgi body carries out two types of functions - 

1. modification of secretions of ER and 
2. production of its own secretions.

• Cisternae contain specific enzymes for specific functions. 
• Refining of product takes place in an orderly manner. 
• For example, glycolipids and glycoproteins that are brought from ER loose certain sugars and regain other, thus forming a variety of products.
• Golgi bodies also manufacture their own products. 
• Golgi bodies in many plant cells produce non-cellulose polysaccharides like pectin. 
• Manufactured or modified, all products of Golgi complex leave cisternae from trans face as transport vesicles.

always remember :

• The cisternae in Golgi body are not physically connected to each other as that are in ER.
• According to recent studies it is proposed that cisternae of Golgi body themselves mature moving from cis to trans face. It is called ‘Cisternal maturation model’.
• It is also said that some vesicles recycle their enzymes that have been carried forward by moving cisternae back to less mature region.
• While they are leaving from the Golgi, certain markers may get impregnated on their membrane so that they can identify their specific target cell or cell organelle.