Golgi apparatus or golgi complex is a cytoplasmic organelle of smooth membranes sac or cisternae, tubules and vesicles. Golgi apparatus is named from Camillo Golgi who discovered it in 1898 in the nerve cells of barn owl and cat by means of impregnation method. The golgi apparatus 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 is formed of a number of unconnected units called dictyosomes.
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 posses four types of components: cisternae, tubules, vesicles and vacuoles.
Function of Golgi Bodies
- Glycosylation occurs inside golgi bodies.
- Carbohydrates (Hemicellulose, Mucopolysaccharides, Pectic compounds) of cell wall matrix are synthesises in Golgi complex.
- Golgi bodies take part in synthesis of special carbohydrates like galactose and sialic acid.
- Chondrottin sulphate and hyaluronic acid are formed by Golgi complex.
- Acrosome is formed by Golgi complex. (It is special structure present near the tip of sperm that contains hydrolytic enzymes for digesting the protective coverings of the egg).
- In oocytes, yolk is deposited around Golgi Apparatus.
- Hormone synthesis of endocrine gland is mediated through Golgi complex.
- Golgi apparatus elaborates toxins present in nematocysts of coelenterates and sting hair of some plants.
- Golgi bodies help in lipid transport.
- In plants, a cell plate is formed in the middle of dividing cell through fusion of vesicles produced by golgi apparatus.
- Lysosomes are formed by golgi apparatus from GERL or maturing face rich in acid phosphatase. (GERL: a complex of Golgi apparatus, Endoplasmic Reticulum and Lysosome)
- The apparatus seem to be involved in formation of root hair from their mother cells.
- Endocytosis brings in pieces of plasma membrane into cytoplasm. E R is continuously adding membranes of Golgi apparatus at its forming face. Golgi apparatus is regularly pinching off membrane pieces in the form of secretion vesicles. The latter add membranes pieces to plasma membrane during exocytosis.
- Golgi apparatus receives membranes from smooth endoplasmic reticulum and transforms the same into coated membranes of coated vesicles, secretion vesicles with membrane thickness of plasma membrane, differentiated resistant membranes of lysosomes etc.
- Function (Secretion )of Golgi complex in different types of cells
Golgi body Functions
|Plant cells||Secretion of protein and cellulose.|
|Exocrine cells of Pancreas||Secretion of Zymogen(Digestive enzymes-protease, lipase)|
|Goblet cells of intestinal mucosa||Secretion of mucus and Zymogens|
|Paneth cells of intestine||Secretion of proteins|
|Brunner’s gland cell or duodenum and ileum||Secretion of mucopolysaccharides.|
|Hepatic cells of liver||Transformation and secretion of lipids|
|Follicle cells of thyroid gland||Prothyroglobulins|
|Plasma cells of blood||Immunoglobulins|
|Cells of alveolar epithelium of mammary glands||Secretion of milk proteins|