Cisternae

A cisterna (plural: cisternae) is any membrane-bound sac found in both the Golgi apparatus and the Endoplasmic Reticulum. Cisterna play an important role in the Golgi protein packaging and modification processes. It is the flattened sac on the Endoplasmic Reticulum branch and the curved sac on the Golgi apparatus branch. 

The proteins enter the Golgi on the cis side (the side facing the ER) and exit on the trans side (the side facing the plasma membrane). Proteins are packaged and modified for transport throughout the cell as they travel through the cisterna. The number of cisterna in the Golgi stack varies according to organism and cell type.Each cisterna’s structure, composition, and function may differ within the Golgi stack. There are three types of Golgi cisternae: cis golgi networks, medial Golgi networks, and trans Golgi networks. 

The cis Golgi network is the first step in the cisternal structure of a protein being packaged, whereas the trans Golgi network is the last step in the cisternal structure when the vesicle is transferred to the lysosome, cell surface, or secretory vesicle. The cytoskeleton of the cell shapes the cisternae via a lipid bilayer. The Golgi undergoes post-translational modifications such as glycosylation, phosphorylation, and cleavage, and as proteins pass through it, they pass through the cisternae, which allow functional ion channels to form.

Functions of Cisternae

The trans-Golgi network is an essential component of the Golgi. It is made up of cisternae and is located on the trans face of the Golgi apparatus. 

The cisternae are essential for the cell’s overall packaging, modification, and transport functions. The proteins and polysaccharides that are processed in the cisterna are then delivered to their designated locations.

There are several types of cisternae, which can be distinguished by their morphology. These distinctions include glycosylation enzymes discovered in cisternae located in different regions of the Golgi. This variation in enzyme localization throughout the cisternae can help the Golgi function by regulating pH, ion concentrations, and the amount of substrate required.

 This also ensures that reactions occur in the correct locations within the Golgi and that proteins do not undergo the incorrect modification if they are in the wrong location.

The cis Golgi network is the first step in the cisternal structure of a protein being packaged, whereas the trans Golgi network is the last step in the cisternal structure when the vesicle is transferred to the lysosome, cell surface, or secretory vesicle. The mannose residue and excess N-acetylglucosamine are removed in the medial cisternae.

Cisternae progression

The progression model, which states that cargo protein transport through the Golgi complex occurs by the progression of cisternae from the cis face to the trans face of the Golgi stack, is a relatively old precursor to the cisternal progression-maturation concept. 4,5 According to this model, the Golgi complex is constantly turning over, allowing a steady flow of membranes from the endoplasmic reticulum to and through the Golgi complex, and then to the plasma membrane.

The membrane flow begins with the exit of membranous that is the carriers containing the cargo proteins from the endoplasmic reticulum and continues with the movement of these membranes to the cis face of the Golgi complex, where they coalesce into a new cis cisternae.

This process is repeated, and at the same time, the trans-most Golgi cisternae disassemble into transport carriers aimed at the plasma membrane. As a result, each cisterna repeatedly shifts its position in the stack until it reaches the trans face. As a result, the cisternae serve as carriers in this intra-Golgi trafficking segment. 

This model is straightforward and elegant, and it accommodated numerous morphological observations from the early decades of electron microscopy (EM). Among these was the presence of large objects known as scales’ in the lumen of certain alga cell cisternae.

Vesicles

The vesicles (60 nm in diameter) are classified into three types:

(i) Transitional vesicles are small membrane-bound vesicles that are thought to form as blebs from the transitional ER and migrate to the cis face of the Golgi, where they coalesce to form new cisternae.

(ii) Secretory vesicles are membrane-limited vesicles of varying sizes that discharge from the margins of Golgi cisternae. They are frequently found between the maturing face of the Golgi and the plasma membrane.

(iii) Clathrin-coated vesicles are spherical protuberances with a rough surface and a diameter of about 50 m. They are found on the organelle’s periphery, usually at the ends of single tubules, and are morphologically distinct from secretory vesicles. Clathrin-coated vesicles are known to play a role in the intracellular traffic of membranes and secretory products, such as between the ER and the Golgi, as well as between the GELR is that region and the endosomal and the lysosomal compartments.

Conclusion

The cis Golgi network is the first step in the cisternal structure of a protein being packaged, whereas the trans Golgi network is the last step in the cisternal structure when the vesicle is transferred to the lysosome, cell surface, or secretory vesicle. The trans-Golgi network is an essential component of the Golgi. It is made up of cisternae and is located on the trans face of the Golgi apparatus. The cis Golgi network is the first step in the cisternal structure of a protein being packaged, whereas the trans Golgi network is the last step in the cisternal structure when the vesicle is transferred to the lysosome, cell surface, or secretory vesicle. The progression model, which states that cargo protein transport through the Golgi complex occurs by the progression of cisternae from the cis face to the trans face of the Golgi stack, is a relatively old precursor to the cisternal progression-maturation concept.