Golgi Apparatus Definition
- The majority of eukaryotic cells include the Golgi apparatus, sometimes referred to as the Golgi body, Golgi complex, or just the Golgi.
- It is referred to as the cell’s shipping and production hub.
- The protein molecules are packaged at the Golgi before being transported to their final location. These organelles serve as the cell’s “post office” by handling and encasing the macromolecules generated by the cell, namely proteins and lipids.
- In the year 1898, Italian researcher Camillo Golgi discovered the Golgi apparatus.
Structure of the Golgi Apparatus
- Under an electron microscope, the Golgi apparatus seems to be composed of stacks of structures with numerous vesicles carrying secretory granules.
- Both plant and animal cells have fairly similar morphologies for the Golgi apparatus. However, it is quite pleomorphic, appearing spread out and reticular in certain cell types and compact and confined in others (net-like).
- However, the Golgi apparatus often takes the form of a convoluted arrangement of interconnected tubules, vesicles, and cisternae.
- The fundamental component of the Golgi apparatus is the cisterna.
- Cisternae are central, flattened, plate- or saucer-shaped, sealed compartments which are kept in parallel bundles or stacks and have a 1 mm diameter.
- Each stack of cisternae is isolated by a 20–30 nm gap that may contain fibres or rod-like components.
- So every stack of cisternae forms a dictyosome, that in plant cells can contain 20 or more cisternae and in animal cells, 5 to 6 Golgi cisternae.
- Each cisterna has a lumen that ranges in diameter from around 500 to 1000 nm and is enclosed by a smooth unit membrane that is 7.5 nm thick.
- Each cisterna’s border is gently curved, providing the entire dictyosome of the Golgi apparatus with the appearance of a bow.
- The proximal, forming, or cis-face consists of the cisternae at the convex end of the dictyosome, whereas the distal, maturing, or trans-face consists of the cisternae at the concave end.
- The dictyosome is encircled by a complex array of similar vesicles and interconnected tubules, from which it radiates (30 to 50 nm in diameter). In reality, the dictyosome’s perimeter possesses a lattice-like (fenestrated) structure.
There are three distinct types of vesicles with a diameter of 60 nm:
(i) Transitional vesiclesare tiny membrane-restricted vesicles which are assumed to arise as blebs move and also converge to the cis face of the Golgi when they conjoin to form new cisternae.
(ii) Secretory vesicles are membrane-restricted vesicles of various sizes that exit the Golgi cisternal borders. They frequently appear between the plasma membrane and the developing face of the Golgi.
(iii) Clathrin-coated vesicles contain spherical protuberances with an approximately 50 m diameter and a rough surface. They are positioned on the organelle’s periphery, frequently at the ends of solitary tubules, and are morphologically distinct from secretory vesicles. It is known that clathrin-coated vesicles are involved in the movement of membranes and secretory products within the cell, namely between the ER and Golgi, the GELR area, and the endosome and lysosome compartments.
Functions of the Golgi Apparatus
- Golgi vesicles are frequently described as the cell’s “traffic police.” They play a key role in organising and directing many proteins and membrane elements of the cell to their proper sites.
- For this purpose, the cis, middle, and membrane proteins as well as glycoproteins which are temporarily present in the Golgi membranes interact with and change as they move to their final locations through the trans cisternae and trans cisternae of the Golgi vesicles.
- For this reason, the Golgi apparatus acts as the cell’s manufacturing facility, where raw materials are transported before being discharged from the cell.
- The Golgi apparatus has a role in the exocytosis and packaging of the following substances in animals:
- exocrine pancreatic cells’ zymogen;
- intestinal goblet cells produce mucus, which is a glycoprotein;
- Mammary gland cells secrete lactoprotein (casein) (Merocrine secretion);
- Thyroid cells’ secretion of thyroxine hormone-related substances (thyroglobulins);
- collagen and tropocollagen secretion.
- formation of pigments, such as melanin, and
- initial oocytes in growth form the vitelline membrane and yolk.
- It also contributes to the development of numerous cellular organelles, including the acrosome of spermatozoa, the plasma membrane, lysosomes, and the cortical granules of various oocytes.
- They assist in the movement of lipid molecules within the cell.
- The synthesis of proteoglycans is another crucial function of the Golgi complex. The extracellular matrix of animal cells contains substances called proteoglycans.
- It is also a significant location for the production of carbohydrates. The creation of glycosaminoglycans, which the Golgi attaches to and subsequently combines with a protein generated in the endoplasmic reticulum to create proteoglycans, is one of these carbohydrates.
- The sulfation of certain substances occurs in the Golgi.
- ATP must be imported into the Golgi lumen in order for the Golgi to phosphorylate molecules.
- The principal function of the Golgi apparatus in plants is to secrete components of primary and secondary cell walls (for example, the production and export of lipids, pectins, and the monomers for hemicellulose, cellulose, and lignin, among others).
- Verma, P. S., & Agrawal, V. K. (2006). Cell Biology, Genetics, Molecular Biology, Evolution & Ecology (1 ed.). S .Chand and company Ltd.
- Stephen R. Bolsover, Elizabeth A. Shephard, Hugh A. White, Jeremy S. Hyams (2011). Cell Biology: A short Course (3 ed.).Hoboken,NJ: John Wiley and Sons.
- Alberts, B. (2004). Essential cell biology. New York, NY: Garland Science Pub.