Golgi apparatus: what it is and what are its parts and functions

Although its name may lead one to think that it is some strange device invented in the country of pizza, the golgi apparatus is an organelle found in our cells, and which is of key importance when manufacturing substances that will be used by the cell.

Already described by Ramón y Cajal and, later, more detailed by his colleague Golgi, the apparatus that bears the surname of the second it acts as a kind of cellular post office: it receives, classifies and sends proteins and other substances. Let's take a deeper look at it.

• Related article: "The Most Important Cell Parts and Organelles: A Summary"

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 is made up of about 80 dictyosomes which, in turn, are made up of more or less 50 saccules or flattened cisterns and surrounded by membrane, stacked one on top of the other, taking care of the modification and completion of some proteins.

As a whole,

this organelle is responsible for acting as a packing plant, modifying the vesicles of the endoplasmic reticulum, in addition to distributing them to the parts of the cell where they touch. It was first described by the Spanish physician Santiago Ramón y Cajal in 1897 and later Camillo Golgi would give detailed descriptions of the device, which would end up being named after him. name.

• You may be interested in: "Camillo Golgi: biography of this revolutionary Italian cytologist"

Structure

As we were already commenting, the Golgi apparatus is made up of stacked cisternae, the number of which can be variable, being between 4 and 8 and forming the dictyosome. In some cells up to 60 stacked cisterns have been seen.

Between these tanks there are tube-shaped connections that allow the passage of substances. The saccules are flattened and curved, with their convex or external face facing the endoplasmic reticulum. They can be grouped into three regions:

1. cis cisterna

The cis cisterna of the Golgi apparatus, also called the cis-Golgi region, is closest to the reticulum. rough endoplasmic, which receives the transitional vesicles that have the proteins that are transform.

2. intermediate tanks

The intermediate cisterns, also called the medial region, are the cisterns that are found in the intermediate zone of the apparatus, between the cis and the trans. It is a transition region, through which the substances that were inside the vesicles will travel.

3. trans cistern

It is the region closest to the plasma membrane and, in fact, its chemical composition is very similar. It is linked to the smooth endoplasmic reticulum.

The vesicles from the endoplasmic reticulum fuse with the cis-Golgi, crossing all the dictyosomes until they reach the trans-Golgi. Here they are packaged and sent to the appropriate place.

The Golgi apparatus is constantly having a flow of molecules that pass through its interior, from the cis to the trans side, passing through the intermediate cisterns.

This makes it an organelle in constant renewal, which affects its size and organization. It should be noted that in those cells that have a secretory function, such as hormonal glands, the organelle will be highly developed.

types of vesicles

The vesicles that transport substances through the Golgi apparatus can be of three types:

1. constitutive

They contain proteins that are going to end up outside the cell through exocytosis., process which will occur in the plasmatic membrane.

2. regulated

They are secretion vesicles that, like those constituting, are destined for the outside of the cell, but not immediately. They will remain stored in the cell waiting for some signal to initiate their exocytosis (regulated secretion).

3. lysosomal

Its destination is the lysosomes, which are organelles generated in the same Golgi apparatus. Lysosomes are responsible for breaking down foreign substances from outside the cell. (cellular digestion).

location and size

In animal cells, the Golgi apparatus is an organelle that is 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 start radially from the centrosome.

In plant cells there is no centrosome. There are numerous underdeveloped Golgi dictyosome-like structures, or even individual cisternae scattered throughout the cytoplasm, acting independently.

The size of the dictyosomes and the cisterns of this organelle is variable, depending on the type of cell in which it is found. In general, their size is between 1 and 3 microns in diameter.

functions

The Golgi apparatus performs several functions, although research suggests that it may perform other functions. The two main ones, as we were already suggesting, have to do with modifying substances and distributing them throughout the body.

1. manufacture of substances

The Golgi apparatus is one of the main glycosylation centers of the cell. They are added and modified to carbohydrates, which will form part of glycoproteins, proteoglycans, glycolipids and polysaccharides..

O-linked oligosaccharides are also added to the hydroxyl groups of amino acids, such as serine, threonine, and hydroxylysine, and sulfate groups to glycosaminoglycans.

Other processes that also take place in this organelle are: palmitoylation, methylation and phosphorylation, to name a few.

They are fundamental organelles for plants, since it is here where the glycoconjugates are synthesized, which, later, they will form part of the cell wall, with the exception of cellulose, synthesized in the membrane plasmatic.

Carbohydrate-related functions are carried out by glycosyltransferases., which are enzymes specialized in adding carbohydrates, and glycosidases, which remove them.

Each cisterna of the Golgi apparatus has a specific role, since they contain special enzymes and carry out the process of synthesis of substances as a sequential reaction.

2. distribution of substances

in the golgi apparatus the distribution of molecules from the endoplasmic reticulum occurs, already synthesized in the organelle itselfeither.

Once they have been processed in the Golgi apparatus, the different molecules are selected and packaged in vesicles, which will go to different places in the cell.

It has recently been discovered that the Golgi apparatus is a calcium storage center, acting as an intracellular signaling platform.

To release the proteins that are formed in the apparatus, it produces two types of vesicles.

On the one hand we have the secret vesicles, which are the ones that carry the proteins to the outside of the cell so that they can be released into the interstitial space or into the bloodstream.

On the other we have storage vesicles or lysosomes, which are vesicles that remain in the cytoplasm until they are exported.

Bibliographic references:

• Farquhar, M. G., Palade, G. AND. (1981). The Golgi apparatus (Complex). The journal of cell biology. 91: 77s-173s.
• Glick, B. S., Luni A. (2011). Models for Golgi traffic: a critical assessment. Cold Spring Harbor perspectives in biology. 3: a005215.
• Vildanova M. S., Wang W., Smirnova E. TO. (2015). Specific organization of Golgi apparatus in plant cells. Biochemistry (Moscow). 79: 894-906.
• Witkos T. M., LoweM. (2017) Recognition and tethering of transport vesicles at the Golgi apparatus. Current opinion in cell biology. 47:16–23.