Some of the main functions of Golgi complex are as follows:
Golgi apparatus appears to play an important role in the storage, packaging and secretion of certain cell products. 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.
In general Golgi complex is of vital importance and serves many functions:
Hirsch et al., have discovered that, when iron sugar is fed to an animal, iron becomes absorbed on Golgi bodies (Kedrowsky). Van Teel has shown that Golgi systems also absorb compounds of Cu and Au (gold). Kedrowsky has shown that Golgi bodies of Opalina can absorb bismutose (compound of albumin and bismuth) and protargol (compound of albumin and silver). Palay and Kartin (1956) have indicated that Golgi complex are concerned with the storage and absorption of lipids.
Thus, Kirkman and Severinghaus state that Golgi apparatus acts as a condensation membrane for the concentration of products produced elsewhere into droplets or granules by losing water, which are transported to the cell surface for export.
These products may be lipids, yolk, bile compounds, enzymes and hormones, etc. The proximity of Golgi and contractile vacuoles in protozoa may confirm the concentration behaviour of Golgi membranes. Golgi membranes may remove water from the products of synthesis during the formation of secretory granules.
The principal function of Golgi complex is secretion. In several types of cells, synthetic products from the rough endoplasmic reticulum are transferred to Golgi region, from where they are liberated from the cell through plasma membrane by pinocytosis. Secretory function of Golgi seems to be well founded experimentally.
Bowen speaks of Golgi apparatus as a great intracellular centre of enzyme formation. Moricard has shown that Golgi body helps in the production of follicular fluid from granulosa cells of ovary.
It may release zymogen granules (inactivated pancreatic enzymes) which arise from cisternae into secretory vesicles. Secretory vesicles containing granules migrate to cell surface where the membrane of the secretory vesicle and the cell membrane merge, releasing the contents into pancreatic ducts from where they pass into intestine as active digestive enzymes.
Golgi body in endocrine cells helps in secretion of hormones. Cowdry has suggested that any harm to Golgi apparatus in thyroid gland cells will result in decline in secretion of its hormone.
Vacuoles and vesicles which are the main components of Golgi complex become filled with protein-lipoid material for storage. These stored products help in secretory action.
It forms the acrosome of sperm during sperm maturation as shown in Fig. 11-2. The cisternae of Golgi complex are arranged in a cup-shaped pattern, the lamellae stacked in parallel. From the periphery of lamellae, small vesicles or vacuoles are pinched off.
Gradually the system of cisternae is replaced by more vesicles and tubules and within some of these vesicles small granules appear. These granules represent secretory products within Golgi complex. Some of the granule-containing vesicles coalesce to form a single acrosome within a large vesicle, which comes to lie on the surface of the sperm nucleus.
In the marine isopod, Limnaria ligmorum, which is a burrowing form, there are present midglands whose cells consist of crystals. These range up to 30ц in length and 15(1 thick. It has been proved that these crystals are formed by Golgi complex and are known to contain protein and iron. They are without enclosing membrane and usually spheroidal in shape. They are concerned with the secretory activity.
In lactating mammary gland of mice are produced protein droplets which are related with Golgi complex. These droplets usually open on to cell surface by fusion of their enclosing membrane with plasma membrane.
Golgi bodies of plant cells synthesize all polysaccharides such as pectin, hemicellulose and microfibrils of a-cellulose. These are packaged in vesicles for secretion. For example, pectin and other mucilaginous substances of the plant cell wall are synthesized in the Golgi and are packaged in vesicles for secretion.
Golgi bodies during mitotic cell division form a cell plate at the centre of spindle. This cell plate is gradually enlarged and thickened by deposition of pectic substances, hemicellulose and micro fibrils of a-cellulose secreted by Golgi bodies.
Glycoproteins are formed in the Golgi complex by the attachment of carbohydrate to the protein products of the endoplasmic reticulum.
After enzymes are synthesized and accumulated in vesicles of endoplasmic reticulum, the vesicles migrate to the Golgi complex, where they fuse with the Golgi membranes. In the Golgi complex, the newly synthesized products of ER are concentrated, and some of the proteins are modified by the addition of carbohydrates or other prosthetic groups.
The concentrated products then accumulate in the edges of Golgi cisternae, where they are packed into small vesicles that bud off from the edges of cisternae and are released into the cytoplasm. Here smaller vesicles may fuse into larger ones. If the vesicles contain secretory product, they will migrate to the plasma membrane, where they release their products into the surrounding environment by exocytosis.