APPARATUS GOLGI

GOLGI APPARATUS (GA) 

Found in almost all eukaryotic cells. Can be seen by using a visible light microscope. At almost every single cell has 10-20 units of Golgi Apparatus. While the plant has Golgi Apparatus almost hundreds, its called dictyosome. Eukaryotic cells consist of one or more stacks of flattened saccules (cisternae) and an array of fenestrae and tubules continuous with the peripheral edges of the saccules. The Golgo Apparatus Initially discovered by Camillo Golgi Italian, in 1897 (Davidson, 2004). 

 I. The Structure of Golgi Apparatus 

A. By using the electron microscope, 

the Golgi Apparatus constructed of stacks of flattened membranous cisternae, or saccula or lumela. The cisternae, tend to be shaped like a disc and have a smooth membrane, whose diameters are tipically 0.5 µm- 10 µm. The thick of membranes cisternae has 75Aº . Saccules stacks is called dictiosome. The length of one saccule to other saccule is 20 nm. A space located in a sac called the lumen. The lumen thick is 15 Aº (Budiono, 2007). Golgi Apparatus have two (2) faces, there are first face is a cis face “formation”, and the second face is a trans face “maturation”. The Golgi membrane structure is almost the same as the Endoplasmic Reticulum membrane and cells membrane structure. It consist, formed by (a) lipda, composed of phospholipids and neutral lipids, (b) protein, consisting of glikopretein and enzymes. The enzymes was into the Golgi marker enzyme is glikosiltransferase, because it found predominantly at the Golgi. The saculi of Golgi complex arrangement varies according to the type of organism, and the physiological of the cells (Issoegianti, 1993). Its more given meaningful of portion of Golgi Apparatus by given from picture 2. 

 In the lumen of dictyosome there is polysaccharides, provided that: a) polysaccharide levels: the surface towards the trans, the levels of polysaccharides is more higher than other surface of dictyosome. b) phosphate enzyme activity: towards the trans, the activity of the enzyme more active than other surface of dictyosome. Golgi Apparatus is polar organelle, that every saccule has different sisternae and also different enzymes. Protein molecules are modified in successive stages, when they move from one saccule to another (Issoegianti, 1993). 

 B. Types of vesicle transport and their functions 

Several distinct classes of coated vesciles has been illustrate: 

1. COPII-Coated Vesciles 

 Move materials from ER “Forward ” to the ER-Golgi Intermediate Compartment (ERGIC) and golgi complex. COP is an acronym for coat proteins. COPII coated vesicles mediate the first leg of the journey through the biosynthetic pathway from the ER to the ERGIC and CGN. The COPII coat contains a number of protein that were first identified in mutant yeast cells that were unable to carry out transport from the ER to the Golgi Complex. Among COPII coat proteins is small G protein called Sar1, Which is recruited specifically to the ER membrane. Each organelle carries a set of receptor proteins that bind only to specific kinds of signal sequences, thus assuring that the information encoded in a signal sequence governs the specificity of targeting )' attached to each of them. It can be done because Ribosomes use mRna as a template which they translate to make a correct polypeptide/ protein (karp, 2010). The Exist sites of the RER cisternae are devoid of ribosomes and serve as places where the first transport vesciles in the biosynthetic patways are formed. 

2. COPI-Coated Vesciles 

Move materials in a retrograde direction (a) from ERGIC and Golgi Stack “backward” toward the ER and (b) from trans golgi cisternaee backward toward to cis Golgi cisternae. 

3. Clatrin-Coated Vesciles 

Moves materials from the TGN to endosomes, lysosomes, and plant vacuoles. They are also move materials from the plasma membrane to cytoplasmic compartement along the endocytic pathway. 

 II. The Function of Golgi Apparatus  

      A. The Main Function of Golgi Apparatus 

          a) Glycosylation. 

The Golgi Apparatus plays a key role in the assembly of carbohydrate component of glycoproteins and glycilipids, that better known as glycosylation. Based on several experiments showed that the Golgi apparatus plays a role in the glycosylation process that has been started by the Endoplasmic Reticulum. Saccharides bound to the protein molecules and lipids in general is D-galactose, D-mannose, a-fukosa, N-acetyl-D-glucosamine, N-acetyl-D-galaktosamin, etc. Glycosylation process has been initiated by the endoplasmic reticulum, then Golgi Appratus  just change a little or enhance ER products. Oligosaccharide molecules bound to the polypeptide can be in two ways: by the bond-N and bond -O. the Two groups-N bond of the oligosaccharide are oligosaccharide-complex and oligosaccharide bind mannoses, it can be bound to the dishware glycoprotein molecules. Sometimes both types of oligosaccharides were linked in the same polypeptide chain. Then the oligosaccharide bind mannoses at the Golgi Apparatus do not acquire additional new monosaccharide. In contrast, the oligosaccharide-complex will get a new monosaccharide. The materials in the addition of oligosaccharide chains derived from the cytosol, while transported to the lumen of the Golgi Apparatus through the transmembrane protein that also plays a role in removing nucleotides product of glycosylation process (denecke. 1990).. 

Based on some experimental results demonstrate that the glycosylation process takes place with varying ways and places. This process occurs in three ways, namely 1) ​​glycosylation of ER followed into Golgi Apparatus 2) glycosylation only in ER, 3) glycosylation only in Golgi Apparatus (Issoegianti, 1993).

b)      Recovery of the cell membrane and secretory. 

Carrier vesicles are stimulated to soon merge with the cell membrane, these vesicles left Golgi Apparatus with a continuous flow. Transmembrane proteins and lipid vesicles will be a new protein and lipid of membrane cells, while the soluble proteins in the vesicles will be secreted into the intercellular space. This is how cells produce proteins and peptodoglikan substance intercellular space. And this secretoty method is called constitutive secretory pathway. 

In the secretory process in cells that occurs as a result of external sign, the compound to be stockpiled in advance secreted in the secretory granules. secretory granules is the result of surface trans Golgi budding. This involves the formation of proteins envelope, such as clathrin.  

Secretion process have been start at the ER, and then transported to the the Cis-Golgi surface by vesicle transport, then further processed and transferred to the Trans Golgi surface. In the trans Golgi network sorting experienced any type of protein or glycoprotein will bud in the form of secretory vesicles. This secretion process in this case takes place by exocytosis, that was fusion between the membrane vesicles with the cell membrane. 

 B)The Specific Function of Golgi Apparatus

There are specifics function: 

1)  forming fragmolplast and cell wall in plants,

 2) formation of the sperm acrosome and lysosomes, and its present in most of the animals.

 1)      forming fragmolplast and cell wall in plants  

Form the walls of plant cells. Cell walls formed during anaphase and telophase of mitosis and meiosis both. Before anaphase, the Golgi complex is outside the coil. During anaphase, Golgi complex vesicles release toward the center of the coil and the hoarding around the threads of the coil. Vesicle contains compounds forming cell wall. Vesicles derived from the Golgi apparatus contains material for the formation of the cell wall. The default destination of soluble proteins and complex carbohydrate has been suggested to be the plasma membrane (Davidson, 2004). Phragmoplast Serve as a formation framework cell plate (cell plate), which is the initial division between the two daughter cells. Cell plate is formed from the fusion of vesicles produced by the Golgi apparatus with microtubules directed by phragmoplast. Phragmoplast also composed of actin filaments.

Phragmoplast and cell walls formed during anaphase when the process of mitosis or meiosis II. during cariocenesis ends, chromosomes separate into two masses are ready to become the nucleus. between these two, there are heaps of pectin and cellulose substances that form slabs or boards in the middle of the cell. hoarding is done by the Golgi via vesicles and then fused. Then the Golgi Apparatus put materials of primary and secondary wall, vesicles released from the Golgi Apparatus and moving to the membrane cells, fuse and release their contents into the cell wall (Boediono, 2007).

 

1)      forming of the sperm acrosome and lysosomes

a.        forming the acrosome sperm.

formed the acrosom. Another function is to form the sperm acrosome contains enzymes to break down the ovum. Acrosome were located in the head of spermatozoa in the anterior nucleus. Golgi body is an organelle that affect acrosome formation through a fusion of vesicles containing material for the acrosome. Whereas membrane vesicles to the acrosome membrane. Acrosome contains a variety of hydrolytic enzymes that are important in the process of fertilization. Without the acrosome, sperm have difficulty penetrating the various membranes that protect the ovum. The process of formation of the acrosome in the sperm head. 

Forming lysosome

Some of these pinched off vesicles also become lysosomes. lysosome formation process there are two sorts, the first is formed directly by the Endoplasmic Reticulum and the second by the Golgi.  lysosomes were first formed by cells and have not been involved in the digestive activity of primary cells called lysosomes. While secondary lysosomes are lysosomes which is the result of recurrent fusion between primary lysosomes with various substrates that boundary the membrane (Albert et al., 1983). As such, secondary lysosomes has been involved in digestive activity in the cell and there its lumens substrate and hydrolytic enzymes. The trans Golgi network (TGN) , which is last stop in the Golgi complex, function as a major sorting station, directing protein to various destinations. The best understood of the post-Golgi pathway is one that carries lysosomal enzymes. Lysosomal enzymes are transported from the TGN in clathrin-coated vesicles.

 

REFERENCES

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