What is Golgi body?
Italian biologist Camillo Golgi, first observed this organelle in the nerve cells, and hence it was named after him. Golgi body is a smooth surfaced, membrane enclosed organelle of eukaryotic cells which is concerned with secretion.
Distribution of Golgi body
Golgi body is found in the eukaryotic cells except only a few including mature mammalian red blood cell. Generally, in secretory cells, a large single Golgi body is found to be located in between the nucleus and cell membrane, such as thyroid cells, pancreatic acinar cells, intestinal mucosal cells etc. on the other hand, in liver cells, nerve cells and various cells of invertebrates and plants, more than one Golgi bodies are present that remain scattered in the cytoplasm. So, the number of Golgi body within a cell is uneven. Animal cells tend to have fewer and larger Golgi body. Plant cells can contain as many as several hundred smaller Golgi body.
Origin of Golgi body
The Golgi body remains connected with the Endoplasmic Reticulum, and it is believed to originate from Endoplasmic Reticulum. Most likely at first, small, membrane enclosed vesicles are formed by budding from the Smooth Endoplasmic Reticulum (SER). These vesicles then join and fuse to form the lamellae of Golgi body. In the cells of some lower plants and animals the Golgi body may be formed from the nuclear membrane and the cell membrane.
Structure of Golgi body
Like the Endoplasmic Reticulum (ER), the Golgi body is also made up of membrane enclosed structures of various shapes. But the shape of Golgi body changes from time to time. Often there have three types of shape of the Golgi body. Those are:
i) Cisternae or Lamellae
iii) Tubules and Vesicles.
Cisternae or Lamellae are membrane bound flattened sacs that remain stacked one above the other. By small gap of about 20-30 nm two adjacent Lamellae are separated. Each lamella is a slightly curved structure so that its one surface is concave and the other is convex. The lamellae of Golgi body are devoid of ribosome and hence are smooth surfaced dissimilar those of Endoplasmic Reticulum.
Vacuoles are the distended and vesicular terminal parts of the Lamellae.
Tubules and Vesicles
The convex surface of the lamellae remains connected to a network formed by fine, branched tubules. The terminals of these tubules swell to form some tiny vesicles. The tubules of Golgi body communicate with the tubules of the Endoplasmic Reticulum. For this reason, Golgi body is also claimed to be a part of Endoplasmic Reticulum
Functions of Golgi body
Generally four types of functions of Golgi body have been noticed. Those are
ii) Formation of Glycoprotein
iii) Formation of other organelles
iv) Sperm maturation.
The chief function of Golgi body is secretion from a cell of protein materials, such as enzymes, hormones etc., that are not easily diffusible through the cell membrane. After being synthesized in the rough endoplasmic reticulum, the secretory proteins pass into the cisternae of Golgi body through the tubules of ER and Golgi body, and are stored in the Golgi vacuoles. From the vacuoles the secretory materials are released in the cytoplasm in the form of membrane bound tiny vesicels. These vesicles then pass towards the border of the cell and fuse with the cell membrane in such a manner that the secretory materials are expelled out of the cell keeping the cell membrane unbroken. By the same mechanism the Golgi body also helps in the release of neurotransmitters and neuro-hormones from nerve cells.
Formation of Glycoprotein
In the synthesis of glycoprotein materials the Golgi body takes part. The protein part of these materials are formed in the rough endoplasmic reticulum, and then combined with the sugar derivatives in the Golgi body to produce Glycoprotein.
Formation of other organelles
The cell wall and cell membrane contain a variety of glycoprotein materials that are formed in the Golgi body. The Golgi body also helps in the formation of lysosomes.
The Golgi body plays an important part in the formation of acrosomal cap of sperms during their maturation.