Golgi Bodies

Introduction

Golgi apparatus was identified in the year 1897 by the Italian scientist Camillo Golgi and in year 1898 it was named after the scientist as Golgi Bodies.  Location and tubular connections of the Golgi apparatus are dependent on microtubules. Golgi apparatus is an organelle found in most eukaryotic cells. Eukaryotic cells are organisms that have a clearly defined nucleus surrounded by the nuclear membrane.

In most of the eukaryotes, the Golgi apparatus is made up of a sequence of compartments and is a collection of fused, flattened membrane enclosed discs known as cisternae which originates from the vesicular clusters that bud off the endoplasmic reticulum. A cell of a mammal contains typically 40 to 100 stacks of cisternae.

The importance of Golgi bodies is to particularly process proteins for secretion, that consists a set of glycosylation enzymes that attach various sugar monomers to proteins because the proteins move through the apparatus.

STRUCTURE OF GOLGI BODIES

The Golgi apparatus itself is structurally segregated with three primary compartments lying between the cis face and the trans face. These faces are biochemically different and the enzymatic content of each segment is markedly different. The cis face membranes are generally thinner than the trans face.

The Golgi apparatus is made up of nearly four to eight cisternae, although in some unicellular organisms it may consist of as many as 60 cisternae. The cis face receives the proteins and lipids that arrive in clusters of fused vesicles. 

These fused vesicles travel along microtubules through a special trafficking compartment, called the vesicular-tubular cluster, which lies between the endoplasmic reticulum and the Golgi apparatus.

When a vesicle cluster fuses with the cis membrane, the products are delivered into the lumen of the cis face cisterna. The proteins and lipids are changed into functional molecules and are ready for delivery to specific intracellular or extracellular locations as they progress from the cis face to the trans face.

Reaching the final stage of transport through the Golgi apparatus, the modified proteins and lipids are sorted in the trans Golgi network and are packaged into vesicles at the trans face. Then these molecules are delivered to their target destinations, such as the cell membranes or lysosomes.

CISTERNAE

The cisterna, plurally cisternae, are the sacs that are membrane bound and could be found in both the Golgi apparatus and in the Endoplasmic Reticulum. They contain specific enzymes creating five functional regions which modify proteins passing through them in a systematic way, as follows:

1. Cis-Golgi network: They forms a connection with the endoplasmic reticulum and is the entry point into the Golgi apparatus. They lie close to the nucleus.

2. Cis-Golgi: Cisternae nearest to the ER which allows biochemical changes.

3. Medial-Golgi: Central layers of Cisternae.

4. Trans-Golgi: Cisternae farthest to ER allowing biochemical modifications.

5. Trans-Golgi network: They are the exit point for vesicles coming out of the Golgi surface, packages and sorts biochemicals into the vesicles according to their locations.

TUBULES

Golgi apparatus of cells are characterized by an extensive system of approximately 30 mm diameter peripheral tubules. The total surface area of the tubules and associated fenestrae is assumed to be approximately equal to that of the cisternae’s flattened portions. The tubules are extended from the stacks for considerable distances. The tubules interconnect differently across the stack but are continuous with the peripheral edges of the stacked cisternae.

Tubules and fenestra cover a large surface area and thus it is reasonable to consider that these components of the golgi apparatus play an important role in the function of golgi apparatus. Tubules interconnect closely with adjacent stacks of the golgi apparatus and may represent a process to synchronise stack function within the cell. 

VESICLES

The vesicles are classified into different types:

• Transitional Vesicles: It helps to move materials such as proteins and other molecules to another cell from one cell. When a cell makes proteins, transporter vesicles help to move these proteins to the golgi apparatus for further refining of the proteins. The Golgi apparatus identifies specific types of transport vesicles and then directs them to wherever needed

• Lysosomes: They are vesicles that contain digestive enzymes. When the cell absorbs harmful substances such as pathogens, it uses lysosomes to ingest those bacteria and destroy them with enzymes

• Secretory Vesicles: They play an important part to move molecules outside the cell through a process called exocytosis. For healthy organ and tissue function they are very crucial

FUNCTION OF GOLGI BODIES

Proteins and lipids that the Golgi apparatus receives from the endoplasmic reticulum are modified in the process. 

Before being delivered to different intracellular or extracellular targets, these biochemicals leave the Golgi bodies by exocytosis.

• Protein processing: Alteration by addition, removal or change of carbohydrates in the carbohydrate regions of glycoproteins

• Lipid processing: For creation of the phospholipids which make up the cell membrane, phosphate groups and glycoproteins are added to lipids from the endoplasmic reticulum

For the formation of certain cellular organelles such as plasma membrane, lysosomes, etc. Golgi bodies are functional. In the transport of lipid molecules around the cell the Golgi apparatus are involved.

The Golgi complex also plays a significant role in the production of proteoglycans. The proteoglycans are molecules that are present in the extracellular matrix of the animal cells. It is also a major location for the synthesis of carbohydrates. The carbohydrates include the synthesis of glycosaminoglycans. Golgi attaches to these polysaccharides which then gets attached to a protein produced in the endoplasmic reticulum to form proteoglycans.

 CONCLUSION

In plants, golgi apparatus is mainly involved in the secretion of materials of primary and secondary cell walls (e.g., formation and export of glycoproteins, lipids and monomers for hemicellulose, cellulose, lignin, etc.) In this article, we have learnt about the various parts involved in the structure of the golgi bodies. The various functions of the golgi apparatus for synthesis of carbohydrates or transport of lipid molecules around the cell are also discussed. The various structures of the golgi bodies are briefly discussed in the article.