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Golgi apparatus

The Golgi apparatus is an organelle present in all eukaryotic cells except red blood cells. It belongs to the endomembrane system. It is made up of structures called dichthyosomes (depending on the type of cell), and these dichthyosomes are made up of about 4 - 8 flattened cisternae (discoidal saccules) surrounded by a membrane that are stacked on top of each other, and whose function is to complete the manufacture. of some proteins. It works as a packing plant, modifying vesicles of the rough endoplasmic reticulum. New membrane material forms in various cisternae of the Golgi apparatus.

The eukaryotic cells possess a Golgi apparatus more or less developed, according to their function. The dictyosomes may have continuity with other components of the endomembrane system, such as the endoplasmic reticulum.

Structure and composition of the Golgi apparatus

The dictyosomes present:

  • CIS face, proximal or of formation: it is the most internal, close to the nucleus, and continuation of the membranes of the endoplasmic reticulum, from which it receives the transition vesicles, which are saccules with proteins that have been synthesized in the membrane of the rough endoplasmic reticulum, introduced into their cavities and transported through the lumen to the outermost part of the reticulum. The contents of the transition vesicles are incorporated into the cisternae of the Golgi apparatus. New vesicles emerge from each cistern and join the next cistern.

Its shape is convex. Their membranes are thin, with a composition similar to that of the endoplasmic reticulum membranes. 

  • An intermediate face or saccules of the central zone, which have the highest metabolic activity. It presents the intermediate or intercisternal vesicles.
  • TRANS, distal or maturing face: it is close to the plasma membrane (it looks more like it). Its shape is concave. On the periphery of this face, there are large vesicles called secretory vesicles, which contain the final products inside and which will lead to the plasma membrane to expel them to the external environment (exocytosis) or to form lysosomes, which contain digestive enzymes.

Golgi apparatus functions

  • Protein transport and concentration (formed mainly in the RE). Proteins from the rough endoplasmic reticulum, encompassed in vesicles, bind to the cis region of the dictyosomeHere, if they are not phosphorylated, the proteins undergo phosphorylation. The secreted proteins move from one tank to another, until they reach the tanks located on the trans face of the dictyosome.
  • Glycosylation of lipids and proteins. The glycosylation that had begun in the ER is completed. In the Golgi apparatus, the assembly of oligosaccharides to lipids and proteins occurs to form glycolipids and glycoproteins, respectively. Glycosaminoglycans are also produced extracellular matrix of animal cells, as well as pectins and hemicellulose of the walls of the cell plant is.
  • Formation of the fragmoplast in plant cells. The telophasic septum that divides the cytoplasm in the equatorial zone of the plant cell, is produced by the association of vesicles derived from the Golgi apparatus.
  • Acrosome formation in sperm. The acrosome derives from the Golgi apparatus. It contains hydrolytic enzymes that serve to digest the components of the ovule coatings during fertilization.
  • Membrane formation (when the contents of the vesicles are expelled through exocytosis, they bind to the plasma membrane, increasing the surface area).
  • Formation of lysosomes.
  • Concentration of substances (carbohydrates, proteins). Collector and transport.

When glycoproteins and glycolipids have been synthesized, they will go to the plasma membrane through the secretory membranes.

The proteins (formed in the RER) and lipids (formed in the REL) are transported to the Golgi apparatus by vesicles transition and there they are passed from saccule in saccule and out through the secretory vesicles transformed into glycolipids and glycoproteins.

The dictyosomes are dynamic structures as sacchules of the Golgi apparatus are constantly renewed by fusion of vesicles of transition from the SR membranes and are transformed sacchules to become secretory vesicles.

Fundamental ideas about the Golgi apparatus

The Golgi apparatus is made up of  dichthyosomes,  each composed of  4-8   flattened membrane-bound cisterns that are stacked on top of each other.

Main function: to complete the manufacture of some proteins from the rough endoplasmic reticulum.

The structure of the dictyosomes is:

  • One face CIS, proximal or formation : 
    • Close to the nucleus, and continuation of the membranes of the endoplasmic reticulum.
    • Convex shape.
    • It receives the transition vesicles, with proteins from the rough endoplasmic reticulum.
    • The content of the transition vesicles is incorporated into the cisternae of the Golgi apparatus, from which new vesicles emerge and are incorporated into the next cistern.
  • An  intermediate face or saccules of the central zone, with intermediate or inter-cisternal vesicles.
  • A  TRANS, distal or maturation face:
    • Near the plasma membrane.
    • Its shape is concave.
    • The secretory vesicles exit towards the plasma membrane to expel the products to the external environment (exocytosis) or to form lysosomes, which contain digestive enzymes.

Golgi apparatus functions:

  • Protein transport and concentration (formed mainly in the RE).
  • Glycosylation of lipids and proteins.
  • Formation of the fragmoplast in plant cells
  • Acrosome formation in sperm
  • Membrane formation.
  • Formation of lysosomes.
  • Concentration of substances (carbohydrates, proteins).