Biological Membranes - A. N. Ogurtsov 2012

Structure and Functions of Biomembranes
Cellular Membrane Structures
Golgi Apparatus

The presence of the Golgi apparatus in The Cell was discovered back in the 19th century, but the investigation of its Functions began comparatively recently.

The Golgi apparatus is a system of intracellular membranes consisting of several discrete Golgi complexes (Figure 12). Each of these complexes represents rows of flattened cisternae arranged parallel to each other at a distance of 20-30 нм, along with secretory vesicles measuring 40-80 нм.

The vesicles are formed at the cisternae by budding off from them. Since the cisternae have a curved shape, two distinct surfaces of the Golgi apparatus are identified: a concave surface (the so-called secreting pole) and a convex surface (the forming pole).

The Golgi apparatus participates in (1) the packaging and transport of certain substances out of the cell, particularly Proteins and Polysaccharides, as well as in (2) the synthesis of various substances and (3) The formation of The Cell wall in plant Cells.

Upon completion of synthesis on the membranes of the rough Endoplasmic reticulum, certain digestive Enzymes are transferred to the Golgi complex from the forming pole side. After passing through the layer of Golgi membranes, they assemble into vesicles that separate from the cisternae, are transported as a secretion within a secretory vesicle to The Plasma Membrane, subsequently fuse with it, and discharge the Contents of the vesicle to the outside.

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Figure 12 - Golgi apparatus: 1 - Golgi vesicles; 2 - Golgi cisternae (lamellae)

Thus, the absorption of substances takes place on the convex surface (the forming pole), while their release occurs on the concave surface (the secreting pole).

The Golgi complex and the membranes of The endoplasmic reticulum are functionally interconnected.

The convex surface, facing The Nucleus, together with the endoplasmic reticulum serves as the site for the synthesis of proteins and Lipids and is functionally linked to the vesicles of the Golgi apparatus that transport these substances.

On the concave surface of the Golgi apparatus, which faces the Cytoplasm, not only are Glycoproteins formed that are necessary for building new cellular structures, but Lysosomes and Peroxisomes are also generated, which participate in The breakdown of cellular elements.

The formation of Lipoproteins in Liver cells, secretory granules in pancreatic cells, and the hormone-regulated secretion of breast milk—all these well-studied processes involve the Golgi apparatus. However, its existence has also been established in cells where secretion processes do not occur. It is hypothesized that in such cases, its functions consist in the synthesis, METABOLISM, and transport of synthesized proteins, CARBOHYDRATES, lipids, and mucopolysaccharides.

A significant portion of the proteins synthesized in Ribosomes on the membranes of the rough endoplasmic reticulum, upon entering the Golgi apparatus, are converted into glycoproteins, which are packaged into secretory granules and subsequently released into the extracellular environment. Carbohydrates accumulate in the Golgi apparatus in the form of soluble oligomers and uronides, whose polymers are capable of strong Swelling. They form part of the mucilages secreted by the Golgi apparatus.

The Synthesis of the mucin portion of mucoproteins takes place within the cisternae of the Golgi apparatus, driven by the presence of enzymes such as galactosyltransferase and УДФ-М-ацетилглюкозаминилтрансфераза.