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Golgi Apparatus Structure and Function in Animal Cell

    In this Golgi apparatus structure and function in animal cell post we have briefly explained about Golgi apparatus of a cell, definition, components, functions and importance.

    Golgi Apparatus Structure and Function in Animal Cell

    Golgi apparatus of a cell or Golgi complex is a cytoplasmic organelle of smooth membranes sac or cisternae, tubules and vesicles. It was identified in 1897 by the Italian scientist Camillo Golgi, in the nerve cells of barn owl and cat by means of impregnation method, and named after him in 1898.

    With the aids of special staining techniques the Golgi bodies were seen as densely stained region of the cytoplasm under the optical microscope. Under the electron microscope the Golgi apparatus of a cell is seen to be composed of stacks of flattened structures which contain numerous vesicles containing secretory granules.

    The Golgi apparatus of a cell is the processing, packaging and secretion organelle of the cell. It is found in all eukaryotic cells with the exception of mammalian erythrocytes, sieve tube elements. Prokaryotic cell do not contain the apparatus. In plants Golgi apparatus of a cell is formed of a number of unconnected units called Dictyosomes.

    The newly synthesized proteins, found in the channels of the rough endoplasmic reticulum are moved to the Golgi body where the carbohydrates are added to them and these molecules are enveloped in a part of the Golgi membrane and then the enveloped molecules leave the cell. The Golgi apparatus hence acts as the assembly factory of the cell where the raw materials are directed to the Golgi apparatus of a cell before being passed out from the cell.

    Definition

    An organelle, consisting of layers of flattened sacs, that takes up and processes secretory and synthetic products from the endoplasmic reticulum and then either releases the finished products into various parts of the cell cytoplasm or secretes them to the outside of the cell.

    The Golgi apparatus of a cell is responsible inside the cell for packaging of the protein molecules before they are sent to their destination. This organelles helps in processing and packaging the macromolecules like proteins and lipids that are synthesized by the cell, sometimes referred as “post office” of the cell.

    Origin

    The intracellular origin of Golgi apparatus of a cell has been a hotly debated subject for many years. Among the proposed sources of new Golgi bodies are: (i) Vesicles dis-patched from the endoplasmic reticulum, (ii) Vesicles dispatched from the outer membrane of the nuclear envelope, (iii) Vesicles formed by invaginations of the plasma membrane, and (iv) Division of Golgi bodies al-ready present in the cell.

    The most widely accepted view is that Golgi apparatus of a cell are formed from vesicles dis-patched from the ER. These vesicles are called transition vesicles Transition vesicles migrate to the forming face of the Golgi apparatus of a cell, fuse there with existing cisterna membranes, and in so doing contribute to the organelle’s growth.

    Golgi Apparatus of A Cell

    Golgi apparatus

    Golgi Apparatus Structure and Function in Animal Cell

    Shape and size of Golgi complex is largely dependent upon type of cell and its physiological state. It is small in muscle cell but it is well developed in secretary cells. Further, it can be compact stack of fenestrated saccules or a diffuse network of lamellae. It possesses four types of components: cisternae, tubules, vesicles and vacuoles.

    The Golgi apparatus of a cell is a major organelle in most of the eukaryotic cells. They are membrane bound organelles, which are sac-like. They are found in the cytoplasm of plant and animal cells.

    The Golgi complex is composed of stacks of membrane-bound structures; these structures are known as the cisternae. An individual stack of the cisternae is sometimes referred as Dictyosome.

    In a typical animal cell, there are about 40-100 stacks. In a stack there are about four to eight cisternae. Each cisternae is a disc enclosed in a membrane, it possess special enzymes of the Golgi apparatus of a cell which help to modify and transport of the modified proteins to their destination.

    The flat sacs of the cisternae are stacked and are bent and semi-circular in shape. Each group of stacks is membrane bound and its insides are separated from the cytoplasm of the cell. The interaction in the Golgi membrane in responsible for the unique shape of the apparatus.

    The Golgi apparatus of a cell is polar in nature. The membranes of one end of the stack are different in composition and thickness to the membranes at the other end.

    One end of the stack is known as the Cis-face, it is the “receiving department” while the other end is the Trans-face and is the “shipping department”. The Cis-face of the Golgi apparatus of a cell is closely associated with the endoplasmic reticulum.

    Function

    1. The cell synthesizes a huge amount of variety of macromolecules. The main function of the Golgi apparatus of a cell is to modify, sort and package the macromolecules that are synthesized by the cells for secretion purposes or for use within the cell.

    2. It is involved in the formation of lysosomes and other enzyme-containing cellular inclusions, and in the formation of secretory granules in cells such as those found in the pancreas, pituitary and mammary glands, and mucous-secreting glands of the intestine and in many other cell types.

    3. They are also involved in the transport of lipid molecules around the cell. The Golgi apparatus of a cell is thus referred as post office where the molecules are packaged, labelled and sent to different parts of the cell.

    4. It mainly modifies the proteins that are prepared by the rough endoplasmic reticulum. The enzymes in the cisternae have the ability to modify proteins by the addition of carbohydrates and phosphate by the process of glycosylation and phosphorylation respectively.

    5. Carbohydrates are synthesized in the Golgi apparatus of a cell. The process of carbohydrate synthesis involves production of polysaccharides and glycosaminoglycans (GAGs).

    6. The long, unbranched polysaccharides and GAGs are attached to proteins in order to form proteoglycans, the molecules that are present in the extracellular matrix of the animal cells.

    7. Sulfation process of certain molecules is an important task carried out by the Golgi apparatus of a cell. The sulfating of substances passing through the lumen of Golgi body is carried out with the help of sulfotransferases.

    8. To carry out the glycosylation and phosphorylation processes, nucleotide sugars and ATP are imported by the Golgi apparatus from cytosol.

    9. Golgi apparatus of a cell plays an important role in the prevention of destruction of cells (or apoptosis). The Bcl-2 genes present in the Golgi are used for this purpose.

    Further Readings

    Reference

    1. https://www.britannica.com/science/Golgi-apparatus
    2. https://thebiologynotes.com/golgi-body/
    3. https://www.examfear.com/notes/Golgi-apparatus.htm
    4. https://www.notesonzoology.com/cytology/golgi-complex
    5. https://teachmephysiology.com/histology/cell-structures/golgi-apparatus/