Golgi Apparatus

Introduction 

The credit for the discovery of the Golgi complex goes to Camillo Golgi, an Italian cytologist. Golgi apparatus is another term for the Golgi complex.  It is the site where the secretory proteins and glycoprotein undergoes modification and  then export. According to the description by Camillo Golgi, the Golgi apparatus is a cell organelle with a characteristic membranous structure.

The Golgi complex is present near the endoplasmic reticulum, close to the cell nucleus. There are up to five to eight flat and disc-shaped cisternae with a stack-like arrangement. The Golgi complex exists in all eukaryotic cells and acts as a center to manufacture and transport cells to the relevant destinations. 

Golgi complex function               

Secretion is the principal function of the Golgi complex. Another term for the Golgi apparatus is the export house of the cells. The Golgi complex accepts proteins from the endoplasmic reticulum in plants and animals. These undergo packaging into vesicles within membranes and then exported to specific destinations. The Golgi complex synthesizes, forms  and processes around 40 to 50 types of biochemical products.  

The following components pass through the structure of the Golgi apparatus at some stage of maturation:

• Secretory proteins and glycoproteins
• Cell membrane proteins and glycoproteins
• Glycolipids
• Cell wall material (in plant cells) 

The following are the significant functions of the Golgi complex:

• Secretion process– During the secretion of cells, the Golgi body receives the material through the cis-face for chemical modification of proteins and lipids to produce glycoproteins and glycolipids. All chemically modified materials are packed in vesicles and discharged from the Golgi apparatus. The process is reverse pinocytosis. 
• Secretion of macromolecules– Golgi apparatus processes macromolecules. It is known as the director of macromolecular traffic. The Golgi complex secretes lactoproteins from mammary glands and zymogen granules from the pancreas. The Golgi complex also mediates the secretion of the hormone by endocrine glands. The Golgi complex also secretes mucilage through roots to lubricate the soil.
• Synthesis and formation– Synthesis of cell wall material, known as polysaccharide synthesis, occurs in the Golgi apparatus. Formation of the cell plate, lysosome and acrosome occurs within the Golgi complex.   

The Golgi apparatus      

A series of flattened membranous pouches (cisternae) having a stacked arrangement is a Golgi complex. It has a well-defined nucleus and can transport, modify  and transport macromolecules to the target destinations. Golgi apparatus is different in structure and shape than normal cells. Therefore it is termed a pleomorphic structure. The cytoplasm surrounding golgi bodies is a ground substance. It is also known as the zone of exclusion. It has no other organelles.

Golgi apparatus has three main compartments between the two faces on either side. The convex surface is cis-face and the concave surface is trans-face. We can notice a structural polarization in the structure of the Golgi complex as there is a clear biochemical distinction between the two faces of the organelle. Both surfaces have different enzymatic content.

We should also note the following four parts of the Golgi complex:

• Cisternae – These membranous pouches have stack-like arrangements containing nodes, a thick and opaque liquid inside
• Tubules– These irregular shaped tube-like structures have branches 
• Vacuoles– These spherical structures are attached to tubules
•  Vesicles– Filled with secretary material, vesicles are spherical and emerge out from tubules

There are up to eight cisternae remaining together because of matrix proteins. Cytoplasmic microtubules support the entire structure of the Golgi apparatus. The cisternae near the endoplasmic reticulum are cis and those situated at the other end are trans. These two ends and the central or medial layer constitute the Golgi complex. Sorting of protein and lipids is a vital task of the Golgi apparatus

Golgi apparatus in animal cell

Golgi complex is present in plants and animals, but the number of these apparatus is variable. The number of Golgi complexes in animals is less, but the size is large. There are hundreds of small Golgi bodies in plants within a cell. The principal function of the Golgi complex in animals is to process, package and release proteins and lipid molecules.

Golgi complex in plants and animals may differ on the following parameters:

• Replication and form during the cell division process
• Nature of Golgi complex within the interphase cell
• Participation of Golgi complex in membrane recycling and endocytosis in animal cells

There is a special trafficking compartment to receive lipids and proteins in clusters of fused vesicles at the cis-face of the Golgi complex for processing. Vesicular cluster’s fusion with the cis-face helps deliver proteins and lipids into the cisternae near the cis-face. The molecules of proteins and lipids undergo specific transformations. These are the removal of monosaccharides or the addition of phosphate groups and fatty acids.

 Conclusion

Golgi complex is an organelle in cells that concentrates, sorts, processes, synthesises, packs and exports the lipids and proteins by receiving from the rough endoplasmic reticulum. The end products are in the form of sealed droplets, which we know as vesicles. These are delivered within cells, outside the cell or to the cell’s plasma membrane. The three main compartments of the Golgi apparatus are cis Golgi reticulum, Golgi stack and trans Golgi network with specific functions.

The Golgi apparatus is a membranous organelle. There are different types of membranes like tubules and vesicles. The Golgi apparatus is close to the endoplasmic reticulum to receive lipids and proteins for further processing. Finished products are delivered in the form of vesicles. The Golgi complex produces new vesicles for continuous delivery of Golgi products to various destinations.