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Golgi Apparatus

The Golgi complex or Golgi apparatus or Golgi bodies are cytoplasmic organelles characteristic in organisation, location and function. The Golgi complex is composed of a system of membrane-bound vesicles found almost in all eukaryotic cells except in some cells such as red blood corpuscles (RBC) of man. It plays an important role in the synthesis, storage and secretion of many materials in the cytoplasm.

The Golgi apparatus was discovered by an Italian cytologist Camilo Golgi in 1898. He described it as a network of threads in the cytoplasm of cells that had been stained with silver nitrate or osmic acid. Later electron microscopic observations revealed the actual structure of the organelle. Golgi complex consists of a system of membrane-bound vesicles of varying sizes arranged in parallel arrays.

Camilo Golgi

In most cells the organelle appears as stacks of flattened sacs (cisternae), each bounded by a smooth surfaced membrane.

Golgi apparatus

Small vesicles of varying sizes are found associated with the cisternae. The Golgi apparatus shows great diversity in size and shape in different cells engaged in the secretion of proteins, carbohydrates or hormones and also in cells concerned with absorptive function such as intestinal cells. The structure of the Golgi apparatus is compact and it is located between the nucleus and the cell surface where secretion or absorption takes place. In plant cells, the Golgi apparatus consists of many unconnected units called dictyosomes. The number of dictyosomes in certain plant cells may be as many as one hundred and in each of the unit is a stack of the Golgi sacs. The cisternae which are equally spaced in the stack are frequently curved either towards the nucleus or to the outer surface of the cell. This gives the Golgi complex a distinct polarity with a convex outer face and a concave inner face.

The most widely established function of the Golgi apparatus is the packaging and transporting of certain materials such as proteins and polysaccharides out of the cell. For many years the Golgi complex was considered to be passive channels to transport materials synthesised elsewhere. However, many of the recent evidences indicate that the Golgi apparatus has many different functions and it is involved in synthesis and secretion of many materials. Many proteins secreted from the cell have carbohydrates attached to them and these are called glycoproteins. The linking of proteins and carbohydrates in the formation of glycoproteins occurs in the Golgi complex. Golgi complex is also involved in the synthesis of some of the polysaccharides. The formation of cell wall of plant cells depends on the activity of the Golgi complex. It also plays a role in the synthesis of substances such as mucus, gums, etc. Several enzymes like glycosyl transferase and thiamine pyrophosphatase have been found to be localised in the Golgi complex.

Apart from synthesis and transport of materials the Golgi complex is also involved in membrane transportation, i.e., changing one type of membrane into another type. Several secretory vesicles or primary lysosomes are produced from the sacs of Golgi complex. Golgi apparatus undergoes certain characteristic changes during the maturation of germ cells. During spermatogenesis the Golgi complex transforms itself into the acrosomal cap of spermatozoa. The sperm acrosome, which is the seat of many enzymes, facilitates the entry of spermatozoan into the egg at the time of fertilization.


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