About Golgi Complex
An Italian scientist Camillo Golgi (1898) described the internal reticular apparatus (apparto reticulareinterno) in the nerve cells of the barn owl as a special cytoplasmic area impregnated with silver nitrate and osmium chloride.
They are found in all eukaryotic cells but absent in some cells like mammalian erythrocytes, sieve tube elements etc. In plant cells, GC consists of a number of isolated units called dictyosomes. In animal cells it occurs as single compact (localized) or loose complex (diffused). The number of dictyosomes is also variable. A rhizoidal cell of aquatic alga chara has upto 25000 dictyosomes while in some simple eukaryotic algae like Micromonas has one only. Golgi complex is surrounded by a zone of cytoplasm which is devoid of mitochondria, chloroplasts and other cell organelles; it is called as zone of exclusion (Moore 1977).
Structure of Golgi Complex
GC possesses four types of components Cisternae, tubules, vesicles and vacuoles.
These are single unit membrane lined curved sac like structure, which occur in a stack of 4-8. Unicisternal dictyosomes occur in fungi, in some algae the stack may have 1020 cisternae, but upto 30 cisternae occur in insects. Curvature gives a polarity to cisternae. There is a proximal, convex, forming surface called as cis face and a distal concave, maturing surface called as trans face. The cis face remains towards endoplasmic reticulum or nucleus while trans face remains towards plasma membrane. The thickness of the membrane of cisterna is less on forming face (50-60Å) but it gradually increasing towards maturing face (7580Å). Each cisterna encloses a space or lumen. The forming face receives transitional vesicles from ER while maturing face bud off their secretion as vesicles or vacuoles.
These are short, branched and inter connected hollow filamentous structures which develop on the sides and maturing face of cisternae. They connect the cisternae and involved in elaboration of secretory products.
These are sac like structure having the diameter of 2080 nm. Vesicles develops from cisternae (trans face) and tubules. They are of two types smooth and coated vesicles.
They are expanded part of cisternae which become modified to form vacuoles. They develop from concave or maturing face.
Functions of Golgi Complex
Glycosylation is the process of addition of polysaccharides to polypeptide chain and lipids which occurs in the Golgi complex.
Lysosomes are produced by Golgi complex.
Simple carbohydrates (galactose), hormones and complex carbohydrates (hemicellulose, pectin, mucopolysaccharides, hyaluronic acid, chondroitin sulphate) are synthesized inside GC.
Golgi complex receives membrane from smooth endoplasmic reticulum and transforms it to plasma membrane, membrane of lysosome, secretory vesicles.
In plant cell it is the precursor of cell plate that helps in division of cell.
During spermiogenesis acrosome is produced by GC.
In oocytes, yolk is deposited around Golgi apparatus. This process is called as vitellogenesis.
The GC also forms nematocysts in Hydra and trichocysts in Paramecium.