The Golgi apparatus is an intracellular reticular structure found in eukaryotic cells; it is the organelle associated with the synthesis of various inclusion bodies. It has a highly variable form; its appearance under the microscope varies from that of a complex netlike structure (a compact form occurring in vertebrates cells) to that of individual sinuous or rodlike bodies (a dispersed form, called a dictyosome, occurring in plants and invertebrates). It was named for the Italian histologist Camillo Golgi.
Research with the electron microscope have shown that the Golgi apparatus comprises three elements: a system of five to eight flat cisternae (γ-membranes), vesicles, and large vacuoles (0.2–0.3 microns in diameter). The Golgi apparatus is located near the endoplasmic reticulum (ER) and the nucleus or around the centrosome. On fixed material, it is revealed by impregnation with silver salts or osmic acid. The organelle contains lipids, lipoproteins, and phospholipids, but is relatively low in enzymes.
Function
The Golgi apparatus is involved with the production of the various formed elements of the cell’s vital activities, such as secretory granules and vitelline lamellae, collagen, lipid, and glycogen inclusions, and melanosomol granules. Deposits of vital dyes, ascorbic acid, iron salts, and colloid silver are observed in the Golgi region. The activity of the Golgi apparatus is also implicated in the production of primary lysosomes, the acrosomes of spermatozoa, and the lamellae of plant cells. The role of the various components of the Golgi apparatus in these processes differs; the vesicles and cisternae are regarded as the functional parts of the Golgi apparatus, while the vacuoles only serve in the transport of substances.
The proteins synthesized on the ribosomes enter the Golgi apparatus through the cisternae of the endoplasmic reticulum, where they are concentrated and packed into granules. In the synthesis of protein products, the Golgi apparatus— the “packing plant”—forms the secretory granules. In the production of carbohydrates (mucopolysaccharides, glycoproteins), the intracellular “conveyor” in effect switches over to another product and the Golgi apparatus participates in the synthesis of polysaccharides. In mucus, bone, and cartilage cells, tagged sugar molecules are first incorporated into the Golgi apparatus and appear in other cell components only later. Sulfation, which is associated with the synthesis of acid mucopolysaccharides, also takes place in the Golgi apparatus.
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| A schematic picture showing an eukaryotic cell, with its organelles that include the Golgi apparatus. |
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| A three-dimensional image of a eukaryotic cell, showing the Golgi apparatus and other organelles. |