The Golgi complex was discovered by Camillo Golgi in 1898. This structure is present in the cytoplasm of almost all eukaryotic (constituent higher organisms) cells, especially secretory cells in animals.
Golgi complex. Structure.
The structure is represented by a stack of flattened sacs of membranes. They are called tanks. This stack of sacs is associated with a system of vesicles ( Golgi vesicles ). From one end of the stacks of pouches, new cisterns constantly form by the fusion of bubbles that bud from the endoplasmic reticulum (network of cavities). From the other end of the stack, from the inside of the tank, maturation is completed and again disintegrates into bubbles. So there is a gradual movement of tanks in the hill to the inner side from the outer side.
In the tanks of the structure, maturation of proteins intended for secretion, transmembrane proteins of the plasma membrane, proteins of lysosomes and others occurs. Ripening substances move sequentially along the tanks of the organelle. They are the final coagulation of proteins and their modifications - phosphorylation and glycosylation.
Plant cells are characterized by the presence of a number of individual dictiosomes (piles). In animal cells, there are often several stacked tubes or one large stack.
The Golgi apparatus (complex) contains four main departments: the trans-Golgi network, the cis-Golgi, the trans-Golgi and the media-Golgi. An intermediate compartment (isolated area) is also attached to the structure. It is represented by an accumulation of membrane vesicles in the gap between the reticulum and cis-Golgi.
The whole apparatus is an organelle very polymorphic (diverse). Even at different stages of the development of a single cell, the Golgi complex may look different.
The apparatus differs in asymmetry. Cisterns (cis-Golgi) located closer to the cell nucleus contain the most immature proteins. These cisterns are joined continuously by membrane vesicles - vesicles. Different tanks contain various resident enzymes (catalytic), which suggests that different processes occur in sequence with ripening proteins.
Golgi complex. Functions
The tasks of the structure include chemical modification and transport of substances entering it. Proteins that enter the apparatus from the endoplasmic reticulum are the starting substrate for enzymes. After concentration and modification, the enzymes in the vesicles are transported to the designated site. For example, it may be the area of formation of a new kidney. With the participation of cytoplasmic microtubules, the transfer process is most active.
The Golgi complex also performs the task of attaching carbohydrate groups to proteins and the subsequent use of these proteins in the construction of the lysosome membrane and cells.
In individual algae, cellulose fibers are synthesized in the structure of the apparatus.
The functions of the Golgi complex are quite diverse. Among them are the following:
- Sorting, removing, accumulating secretory products.
- The accumulation of lipid molecules and the formation of lipoproteins.
- Completion of protein modification (post-translational), namely glycosation, sulfation, and more.
- The formation of lysosomes.
- Participation in the formation of acrosomes.
- Polysaccharide synthesis for the formation of waxes, glycoproteins, mucus, gum, matrix substances in the cell walls of plants (pectins, hemicelluloses and others).
- Formation of contractile vacuoles in protozoa.
- Cell plate formation in plant cells after nuclear division.