Although the name may make you think that it is a strange device invented in the land of pizza, the Golgi apparatus is an organelle found in our cells, And that it has a key importance when making substances that will be used by the cell.
Already described by Ramón i Cajal and later in more detail by his colleague Golgi, the device bearing the latter’s surname acts as a sort of cell post office: it receives, classifies and sends proteins and other substances. Let’s take a closer look.
What is the Golgi apparatus?
The Golgi apparatus is an organelle found in all cells of eukaryotic organisms, And belongs to the cellular endomembrane system. It consists of about 80 dictyosomes which, in turn, are formed from about 50 flattened, membrane-surrounded sacs or cisterns, stacked on top of each other, responsible for the modification and completion of some proteins.
In general, this organelle is responsible for acting as a packaging plant, Modify the vesicles of the endoplasmic reticulum, as well as distribute them to the parts of the cell where it belongs. It was first described by the Spanish physician Santiago Ramón i Cajal in 1897 and later Camillo Golgi gave detailed descriptions of the device, which would eventually be named after him.
As we said already, the Golgi apparatus consists of stacked cisterns, the number can be variable, being between 4 and 8 and forming the dictyosome. In some cells, up to 60 stacked tanks were seen.
Between these cisterns there are tube-shaped connections that allow the passage of substances. The sacs are flattened and curved, with their convex or outer face oriented towards the endoplasmic reticulum. They can be grouped into three regions:
1. Cisterna cis
The cis cistern of the Golgi apparatus, also called the cis-Golgi region, is closest to the rough endoplasmic reticulum, which receives the transition vesicles containing the transformed proteins.
2. Intermediate tanks
Intermediate cisterns, also called medial region, Are the cisterns which are in the intermediate zone of the apparatus, between the cis and the trans. This is a transitional region through which the substances that were inside the vesicles will travel.
3. Trans tank
It is the region closest to the plasma membrane and, in fact, its chemical composition is very similar. It is attached to the smooth endoplasmic reticulum.
The vesicles of the endoplasmic reticulum fuse with the cis-Golgi, crossing all the dictyosomes to reach the trans-Golgi. Here they are packaged and sent to the appropriate place.
The Golgi apparatus has constantly a flow of molecules passing through its interior, from the cis side to the trans, through the intermediate reservoirs.
This is done by an organelle in constant renewal, which affects its size and organization. It should be noted that in cells that have a secretion function, such as hormonal glands, the organelle will be highly developed.
Types of blisters
The vesicles that carry substances through the Golgi apparatus can be of three types:
They contain proteins that will go outside the cell by exocytosis, Process that will occur in the plasma membrane.
These are secretory vesicles which, like the constituentsThey are intended for the outside of the cell, but not immediately. They will remain stored in the cell while waiting for a signal to start their exocytosis (regulated secretion).
Their destination is lysosomes, which are organelles generated in the same Golgi apparatus. Lysosomes are responsible for breaking down external substances from outside the cell. (Cellular digestion).
Location and size
In animal cells, the Golgi apparatus is an organelle located near the centrosome, which in turn is usually near the nucleus. The central position of the Golgi apparatus depends on the organization of the microtubule system that make up the cytoskeleton, which in animal cells diverge radially from the centrosome.
There is no centrosome in plant cells. There are many structures similar to underdeveloped Golgi dictyosomes, Or even individual cisterns scattered throughout the cytoplasm, acting independently.
The size of the dictyosomes and cisterns of this organelle is variable, depending on the type of cell in which it is found. Typically, its size is between 1 and 3 microns in diameter.
The Golgi apparatus serves several functions, although research suggests that it may serve others. The two main ones, as we said already, concern the modification of substances and their distribution throughout the body.
1. Manufacture of substances
The Golgi apparatus is one of the main glycosylation centers in the cell. They are added and changed into carbohydrates, which will be part of glycoproteins, proteoglycans, glycolipids and polysaccharides..
O-type oligosaccharides are also added to hydroxyl groups of amino acids, such as serine, threonine and hydroxylisine, and sulfate groups to glycosaminoglycans.
Other processes that also take place in this organelle are: palmitoylation, methylation and phosphorylation, to name a few.
These are fundamental organelles for plants, because it is there that the glycoconjugates are synthesized which will later become part of the cell wall, with the exception of cellulose, which is synthesized in the plasma membrane.
Carbohydrate-related functions are provided by glycosyltransferases, Which are enzymes specializing in the addition of carbohydrates and glycosidases, which eliminate them.
Each cistern of the Golgi apparatus plays a specific role, as it contains special enzymes and carries out the process of substance synthesis as a sequential reaction.
2. Distribution of substances
In the Golgi apparatus the distribution of molecules of the endoplasmic reticulum occurs, already synthesized in the organelle itselfO.
Once they have been processed in the Golgi apparatus, the different molecules are selected and packaged in vesicles, which will be directed to different places in the cell.
It was recently discovered what the Golgi apparatus is a calcium storage center, acting as an intracellular signaling platform.
To release the proteins that form in the device, it produces two types of vesicles.
On the one hand, we have the secret vesicles, which are those that transport proteins outside the cell so that they are released into the interstitial space or into the bloodstream.
On the other hand, we have storage vesicles or lysosomes, which are vesicles that stay in the cytoplasm until they are exported.
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- Glick, BS, Monday A .. (2011). Models for Golgi Traffic: A Critical Appraisal. Cold Spring Harbor Perspectives in Biology. 3: a005215.
- Vildanova MS, Wang W, Smirnova EA (2015). Specific organization of the Golgi apparatus in plant cells. Biochemistry (Moscow). 79: 894-906.
- WitkosTM, Lowe M. (2017) Recognition and fixation of transport vesicles in the Golgi apparatus. Current opinion in cell biology. 47: 16-23.