Golgi Body (Golgi Complex): Structure, Function, and Diagram

The Golgi body is a cellular organelle found in most eukaryotic cells. The Golgi body is also known as the Golgi complex, Golgi apparatus, lipochondrion, Barker’s body, and Dalton complex. In 1898 Italian zoologist Camillo Golgi first described the Golgi complex in the nerve cells of owl and cat. It was known as the internal reticular apparatus. Later in 1910, it was named after him.

The structure of the Golgi body is made up of smooth membrane saccules or cisternae, tubules, vesicles, and golgian vacuoles. Golgi body packs the protein and lipids in the vesicles and secrets them. Proteins that exit from the endoplasmic reticulum enter the Golgi body. Then the Golgi body makes the vesicles in which these proteins and lipids are packed and carried to the other cellular parts like plasma membrane, lysosomes, or secreted from the cell. Before being known as the “Golgi apparatus,” it was also named the “Golgi-Holmgren ducts” and the “Golgi-Kopsch apparatus.” Golgi complex may have distinct subunits: the Golgiosomes, idiosomes, or dictyosomes. In plants and lower invertebrates, it is also known as dictyosome.

Distribution

The Golgi body is not found in the prokaryotes, but it is present in the eukaryotes. In the eukaryotes, the Golgi body is found in all cells except male gametes of bryophytes and pteridophytes, mature sieve tubes, and red blood cells of animals.

Form, size, and number

The Golgi body is found in different shapes and sizes based on its location in the cell. Since its polymorphic, it can change its shape. The number of the Golgi body depends on the type of the cell. In some algae, only one Golgi body is present, whereas, in a plant cell, it may be up to 25000.

Structure of Golgi body

The Golgi body consists of the cisternae, tubules, vesicles, and golgian vacuoles.

Cisternae

The functional unit of the Golgi body is the cisterna. Cisternae are also known as the saccules or lamellae. They are 4-8 membrane lined curved but are flattened disc-shaped inter-connecting cisternae. In the fungi, unicisternal dictyosomes are found. The membrane of the cisternae are smooth, but they vary in their thickness. The margins of each cisterna are frequently curved. One face of the Golgi body is convex while the other is concave. The proximal end has the convex side, known as the forming face or cis-face. This is directed towards the nucleus. At this end, cisternae constantly receive vesicles (also called transitional vesicles) from the smooth endoplasmic reticulum. The other face of the Golgi body is the concave face or distal face cisternae, which are directed towards the plasma membrane. It is called maturing or trans-face. The membrane is continuously lost in the distal cisterna by forming the vesicles and the golgian vacuoles. The loss is compensated by the entry of transitional vesicles into the proximal region. The process of passage of the membrane from the proximal to the distal end of the Golgi body is called membrane flow. In a stack, the adjacent cisternae are separated by a distance of 100-300 Å. The intracisternal space contains a thin layer of cytoplasm having parallel fibers without ribosomes, mitochondria, chloroplasts, and storage granules. It is called a zone of exclusion.

Tubules

Tubules are short, branched, and filamentous substructures on cisternae. They are interconnected, a complicated network that develops on the peripheral sides and maturing face of cisternae. Tubules interconnect with different cisternae. They are mainly involved in the elaboration of secretary products.

Vesicles

Vesicles are the small sacs that develop from the tubules. There are two types of vesicles: smooth and coated vesicles. Smooth vesicles are also called secretory vesicles because they contain secretory products. They bud off from the tubules within the network. On being pinched off, they pass into the cell membrane and help in exocytosis. The coated vesicles are covered by fine bristle-like outgrowths, making the surface rough. They bud off from the ends of peripheral tubules, pass to the cell membrane and help in endocytosis.

Golgian vacuoles

The concave side of distal cisternae produces large rounded vesicles or sacs, known as golgian vacuoles. Some of the golgian vesicles function as lysosomes.

Functions of Golgi body

The major function of the Golgi body is secretion. It secrets gum, mucus, sweat, tears, saliva, etc.
Different substances like proteins, pro-enzymes, lipids, steroids, and other substances pass from the endoplasmic reticulum to the Golgi complex either directly or through the transitional vesicles. Golgi complex concentrates, modifies, and packages all the bio-chemicals into the secretion vesicles, which later pinch off and pass out the secretory bio-chemicals through exocytosis or reverse pinocytosis.
It helps in the transformation of one type of membrane into another type. It converts the membrane of the endoplasmic reticulum into the selectively permeable plasma membrane, a differentiated membrane of the lysosome, etc. It also helps in the recycling of cell membranes.
In Golgi bodies, post-translational modifications and enzymatic processing, such as glycosylation and phosphorylation, take place close to the membrane surface.
In plant cells, a cell plate is formed in the middle of the dividing cell by the fusion of vesicles produced by the Golgi complex.
Complex polysaccharides for the plant cell wall are made in the Golgi apparatus.
Some of the vesicles or vacuoles of the Golgi complex store digestive enzymes obtained through ER in the inactive state, which later function as primary lysosomes.
The vesicles of the Golgi complex form acrosomes of sperms.
It helps in the formation of root hairs from their mother cells.
The membrane of the Golgi complex’s vesicles helps form a plasma membrane after cytokinesis.

References

Alberts, B. (2004). Essential cell biology. New York, NY: Garland Science Pub.
Verma, P. S., & Agrawal, V. K. (2006). Cell Biology, Genetics, Molecular Biology, Evolution & Ecology (First edition). S . Chand and Company Ltd
Shakya M, Mehata KR, Gautam MK, Pokhrel KR and Khanal K (2020 ) “ Principles of Biology”, Asmita Books Publisher and Distributors Ltd, Bhotahity, Nepal