The functioning of the cell depends on various organelles, each with specific functions (Rothschuh Osorio, 2022). Among these, one organelle stands out in particular, acting like a small factory responsible for the production, distribution, and packaging of cellular molecules. According to Rothschuh Osorio (2022), this organelle is known as the Golgi Apparatus, although it is also referred to as the Golgi Complex or Dictyosome.
What is the Golgi Apparatus?
The Golgi apparatus is an organelle present in all eukaryotic cells and is part of the cell’s endomembrane system (Rubio, 2020). This organelle is composed of approximately 80 dictyosomes, which in turn consist of around 50 flattened, membrane-enclosed sacs or cisternae, stacked on top of each other. Its main function is to modify and complete certain proteins (Rubio, 2020). It is important to note that the term "apparatus" refers to the grouping of several elements that work together to perform the same function (Porto & Gardey, 2015). In line with Porto & Gardey (2015), several cellular apparatuses exist, such as the Golgi apparatus.
In animal cells, this organelle is well developed, with cisternae of considerable size (Rothschuh Osorio, 2022). In contrast, in plant cells, Golgi apparatuses are less developed, more dispersed, and their cisternae are smaller. In yeast cells, no well-defined cisternae are found (Rothschuh Osorio, 2022). The Golgi apparatus functions as a packaging plant, modifying vesicles from the endoplasmic reticulum and distributing them to different parts of the cell where they are needed (Rubio, 2020). According to Rubio (2020), this organelle was first described in 1897 by Santiago Ramón y Cajal, and later, Camillo Golgi provided more detailed descriptions, leading to the apparatus being named after him.
Structure
The Golgi apparatus is composed of stacked cisternae, which range from 4 to 8 in number, forming what is known as a dictyosome (Rubio, 2020). These cisternae are connected by tubes that allow the exchange of substances. The sacs forming the cisternae are flattened and slightly curved. The Golgi apparatus can be divided into three main regions. The cis cisterna, also known as the cis-Golgi region, is the area closest to the rough endoplasmic reticulum, where it receives transition vesicles containing proteins to be transformed. The intermediate cisternae are located between the cis and trans cisternae. In this transition zone, substances travel through the cisternae towards their final destination. Lastly, the trans cisterna is the region closest to the plasma membrane, whose chemical composition is very similar to the latter. According to Rubio (2020), it is linked to the smooth endoplasmic reticulum and is responsible for packaging and sending substances to their final destination.
Types of Vesicles
The vesicles that transport substances through the Golgi apparatus are classified into three types (Rubio, 2020). Constitutive vesicles contain proteins that will be released outside the cell by exocytosis. Regulated vesicles are also destined for secretion outside the cell, but they remain stored within the cell until a specific signal activates their exocytosis. Finally, according to Rubio (2020), lysosomal vesicles are directed to lysosomes, where they break down external substances, fulfilling a role in cellular digestion.
Location and Size
The Golgi apparatus is located in the cytoplasm, near the plasma membrane, the endoplasmic reticulum, and the nucleus (Rothschuh Osorio, 2022). Its structure is crescent-shaped, composed of several sacs whose number varies depending on the type of cell (Rothschuh Osorio, 2022). In animal cells, it is located near the centrosome, which in turn is often close to the nucleus (Rubio, 2020). The central position of the Golgi apparatus is related to the organization of the cell’s microtubule system, which radiates from the centrosome. In plant cells, there is no centrosome, and instead, structures similar to dictyosomes are scattered throughout the cytoplasm, acting independently. According to Rubio (2020), the size of the Golgi apparatus varies depending on the type of cell, generally ranging between 1 and 3 microns in diameter.
Functions
The Golgi apparatus performs various essential functions, and research suggests it may have additional roles (Rubio, 2020). This organelle is responsible for packaging, labeling, storing, and distributing products it receives from the endoplasmic reticulum, another fundamental cellular component (Rubio, 2020). Among the products it processes are proteins and lipids, which undergo a modification process that can involve the removal of sugar monomers or alteration of portions, allowing them to be used within the cell (Rothschuh Osorio, 2022). According to Rothschuh Osorio (2022), glycolipids, proteoglycans, and polysaccharides are also generated through this process known as protein glycosylation, facilitating their transport to other cellular structures or their secretion, which is vital for gland function and regulation in the organism.
Packaging Function
The process within the Golgi apparatus follows a specific sequence (Rothschuh Osorio, 2022). First, it receives vesicles containing macromolecules from the endoplasmic reticulum. These vesicles fuse with the cisternae of the cis face of the apparatus, where each cisterna carries out different stages of processing and packaging. Then, the vesicles mature and are transported to the trans face, from where they are sent to various parts of the cell. Typically, the final destination is the plasma membrane. Additionally, according to Rothschuh Osorio (2022), the process is not static, as the cisternae move during maturation, and molecules can be recycled for reuse.
Labeling Function
For molecules to be directed correctly, the Golgi apparatus uses a labeling system that adds phosphate groups as molecular identifiers (Rothschuh Osorio, 2022). According to Rothschuh Osorio (2022), this helps determine whether the products should be sent to another organelle, stored, or reprocessed.
Substance Manufacturing
The Golgi apparatus is one of the main centers of glycosylation in the cell (Rubio, 2020). Sugars are added here to form glycoproteins, proteoglycans, glycolipids, and polysaccharides (Rubio, 2020). This organelle also performs other processes, such as palmitoylation, methylation, and phosphorylation. Additionally, it is essential in plants, where it synthesizes glyconjugates that are part of the cell wall, except for cellulose, which is synthesized in the plasma membrane. This process involves specialized enzymes called glycosyltransferases, which add sugars, and glycosidases, which remove them. According to Rubio (2020), each cisterna in the Golgi apparatus has a specific role and performs these tasks sequentially.
Substance Distribution
In addition to manufacturing and modifying substances, the Golgi apparatus is responsible for distributing molecules from the endoplasmic reticulum or those synthesized within it (Rubio, 2020). These molecules are packaged into vesicles that are transported to different areas of the cell. It has also been discovered that the Golgi apparatus acts as a calcium storage center and plays a role in intracellular signaling. According to Rubio (2020), for protein release, it produces two types of vesicles: secretory vesicles, which transport proteins outside the cell, and storage vesicles, or lysosomes, which remain in the cytoplasm until export.
References
Porto, J. P., & Gardey, A. (2015, noviembre 17). Aparato de Golgi. Definición.de; Definicion.de. https://definicion.de/aparato-de-golgi/
Rothschuh Osorio, U. (2022, febrero 15). Aparato de Golgi: Definición y Función. ecologiaverde.com. https://www.ecologiaverde.com/aparato-de-golgi-definicion-y-funcion-3760.html
Rubio, N. M. (2020, marzo 9). Aparato de Golgi: Qué es y Cuáles son sus Partes y Funciones. Psicologia y Mente. https://psicologiaymente.com/salud/aparato-de-golgi
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