The Golgi Apparatus

Introduction

The Golgi apparatus (GA), also called Golgi body or Golgi complex and found universally in both plant and animal cells, is typically comprised of a series of five to eight cup-shaped, membrane-covered sacs called cisternae that look something like a stack of deflated balloons. In some unicellular flagellates, however, as many as 60 cisternae may combine to make up the Golgi apparatus. Similarly, the number of Golgi bodies in a cell varies according to its function. Animal cells generally contain between ten and twenty Golgi stacks per cell, which are linked into a single complex by tubular connections between cisternae. This complex is usually located close to the cell nucleus.

The Golgi apparatus processes proteins which are always focused to the plasma are always focused to the plasma membrane or endosome. It also sorts various proteins within vesicles and helps them to deliver throughout the cell via endoplasmic reticulum. Eukaryotic cells are the place where Golgi apparatus is found. They are also found mostly near heavy protein concentration. Plasma-B cells which secrete protein antibodies have prominent Golgi apparatus.

Proteins are transported by Golgi apparatus, but it is not completely understood about the way it does it. It is possible that the apparatus itself moves through cisternae progression, or that proteins diffuse from one cisternae to the next.

Golgi apparatus’s functioning is the modification of glycoproteins used in the construction of the cell membrane. It takes simplified glycosylated proteins from the vesicles and creates a diversity of carbohydrate structures on proteins for a variety of uses. [1]

Morphology

The term morphology is generally attributed to the German poet, novelist, playwright, and philosopher Johahnn Wolfgang von Goethe (1749-1832) who coined it early in the nineteenth century in a biological context. Its etymology is Greek: morph-means shape, form, and morphology is the study of form or forms. In biology morphology refers to the study of the form and structure of organisms, and geology it refers to the study of the configuration and evolution of land forms. In linguistics morphology refers to the mental system involved in word formation or to the branch.[3]

The Golgi apparatus

Golgi apparatus was one of the first organelles ever observed because of it large organelle size and shape. In 1897, an Italian physician named Camillo Golgi investigated and developed Golgi apparatus. Many scientists did not believe that what Golgi observed was a real organelle present in the cell and instead argued that the apparent body was a visual distortion caused by staining. The invention of the electron microscope in the twentieth century finally confirmed that the Golgi apparatus is a cellular organelle.

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The Golgi apparatus is often considered the distribution and shipping department for the cell’s chemical products. It modifies proteins and lipids (fats) that have been built in the endoplasmic reticulum and prepares them for export outside of the cell or for transport to other locations in the cell. The vesicles fuse with the Golgi membranes and release their internally stored molecules into the organelle. Once inside, the compounds are further processed by the Golgi apparatus, which adds molecules or chops tiny pieces off the ends. When completed, the product is extruded from the GA in a vesicle and directed to its final destination inside or outside the cell.

The modifications to molecules that take place in the Golgi apparatus occur in an orderly fashion. Each Golgi stack has two distinct ends, or faces. The cis face of a Golgi stack is the end of the organelle where substances enter from the endoplasmic reticulum for processing, while the trans face is where they exit in the form of smaller detached vesicles. Consequently, the cis face is found near the endoplasmic reticulum, from where most of the material it receives comes, and the trans face is positioned near the plasma membrane of the cell, to where many of the substances it modifies are shipped. The chemical make-up of each face is different and the enzymes contained in the lumens (inner open spaces) of the cisternae between the faces are distinctive.

Proteins, carbohydrates, phospholipids, and other molecules formed in the endoplasmic reticulum are transported to the Golgi apparatus to be biochemically modified during their transition from the cis to the trans poles of the complex. Enzymes present in the Golgi lumen modify the carbohydrate (or sugar) portion of glycoproteins by adding or subtracting individual sugar monomers. In addition, the Golgi apparatus manufactures a variety of macromolecules on its own, including a variety of polysaccharides. The Golgi complex in plant cells produces pectins and other polysaccharides specifically needed by for plant structure and metabolism. The products exported by the Golgi apparatus through the trans face eventually fuse with the plasma membrane of the cell. Among the most important duties of the Golgi apparatus is to sort the wide variety of macromolecules produced by the cell and target them for distribution to their proper location. Specialized molecular identification labels or tags, such as phosphate groups, are added by the Golgi enzymes to aid in this sorting effort. [4]

Shape of Golgi apparatus

The Golgi apparatus looks like a stack of pancakes, and these stacks are called Cisternae. The cisteria is filled with central liquid-filled area and made up of two – layer membrane. Usually 4 to 8 consist in a single Golgi complex, but in some organisms there can be as many as sixty. The number of Golgi complexes in each animal cell is typically between ten and twenty.

The Golgi apparatus is not attached to any other organelle, but floats freely in the cell. There are two ends for each Golgi body, one is cis face and the other is trans face. The cis face is closest to the nuclear membrane and the endoplasmic reticulum, while the trans face is oriented outward toward the plasma membrane of the cell.

The Functions of the Golgi apparatus

The primary functions of the Golgi complex are processing proteins synthesized in the endoplasmic reticulum (ER) and directing molecules made in various areas of the cell to their future locations in or out of the cell.

Some of the modifications made inside the Golgi complex include:

• Attaching polysaccharides to proteins to form carbohydrates
• To cut protein into smaller active fragments
• Incorporating phosphates onto protein molecules
• Addition of a sulphate group to molecules

In addition to modifying molecules made elsewhere in the cell, the Golgi apparatus also makes a few of its own products. Some of the most important molecules created in the Golgi complex are the Lysosomes, molecules that operate to digest dead or unnecessary components in the cell, thereby keeping the cell clean and free of debris, and complex sugars. [2]

References

1. http://www.iscid.org/encyclopedia/Golgi_Apparatus
2. http://biology.suite101.com/article.cfm/the_golgi_apparatus#ixzz0Tql0t3N6
3. http://www.absoluteastronomy.com/topics/Johann_Wolfgang_von_Goethe
4. http://micro.magnet.fsu.edu/cells/golgi/golgiapparatus.html
5. http://books.google.co.uk/books?id=l4soWecaclsC&pg=PA1&lpg=PA1&dq=what+is+morphology+%3F&source=bl&ots=LoFNJcVXo&sig=fAAjFKqT6xqXWGMSnoFuTn0ENTw&hl=en&ei=pe3USuGuH9Kq4QaVo_XRDA&sa=X&oi=book_result&ct=result&resnum=4&ved=0CBkQ6AEwAw#v=onepage&q=&f=false