Thursday, October 16, 2014
Diseases Associated with the Golgi Apparatus
Alzheimer’s disease is linked to the Golgi body in that, as the disease progresses the Golgi apparatus becomes fragmented, rendering it incapable of modifying and transporting proteins and lipids like it normally does. Batten Disease is also linked to the Golgi because the source of the disease, the batten disease protein, localizes around the Golgi and researchers believe there is a connection between the two. Batten disease is an inherited and fatal neurodegenerative disease. The Inclusion Cell or I-Cell disease is caused by defective phosphotransferase, an enzyme involved in adding phosphate groups to tell the protein where to go. Without it, proteins that should be going to the lysosome (which function as catabolic enzymes for the normal breakdown of substances in lysosomes) are excreted from the cell and the lysosome is unable to break down cell waste.
Peripheral blood lymphocyte appearance in a case of I-cell disease
The Golgi Apparatus and Lysosomes
The Golgi body creates lysosomes. The Golgi receives lysosomal enzymes from the ER like a regular proteins to be modified, however, when leaving the organelle they are not put in a regular transportation vesicle. Their vesicle membrane becomes the organelle membrane, and the departing vesicle essentially is the lysosome.
How does the Golgi Apparatus modify biomolecules?
The Modification Process:
- Vesicles containing proteins made in the ER move from the ER to Golgi body
- Vesicles coalesce to form new cis Golgi cisternae (a vesicle that buds from the ER can add its membrane and contents of its lumen to the cis face by fusing with a Golgi Membrane)
- Cisternal maturation occurs: Golgi cisternae move in a cis-to-trans direction. As the cisternae move, they encounter different enzymes that are responsible for modifying the structure of the proteins and lipids
- Vesicles form and leave Golgi, carrying specific proteins to other locations or to plasma membrane for secretion
- Vesicles transport some proteins backward to less mature Golgi cisternae, where they function
One example of modification of biomolecules by the Golgi Apparatus includes:
Glycosylation, the process in which various Golgi enzymes modify the carbohydrate portions of glycoproteins. The steps of glycoslyation are
- Carbohydrates first added to proteins in rough ER, during process of polypeptide synthesis
- the carbohydrate on resulting glycoprotein is then modified as it passes through rest of ER and Golgi
- Golgi removes some sugar monomers and substitutes others, producing a large variety of carbohydrates.
Final Shipping Process:
Before a Golgi stack sends its products via vesicles that have budded from the ‘trans’ face, it sorts these products and targets them for various parts of the cell. Different enzymes add “molecular identification tags” such as phosphate groups to Golgi products, that aid in sorting much like zip codes on mailing labels. In addition, transport vesicles that have budded from Golgi may have external molecules on their membranes that recognize “docking sites” on the surface of specific organelles or on the plasma membrane
Important Note: many macromolecules are manufactured by Golgi itself. For example, polysaccharides such as pectin are Golgi products.
Structure of the Golgi Apparatus
The Golgi is a membrane bound organelle characterized by it’s pancake-stack like structure. These “pancake stacks” are cisternae or membrane sacs. There can be anywhere from 5-60 per Golgi, but there is typically only 5-9. The cisternae are split into 5 sections, the cis-Golgi network, cis-Golgi, medial-Golgi, trans-Golgi, and trans-Golgi network. The cis-Golgi network is the receiving section and the trans-Golgi network is the sending section of the organelle.
Where is the Golgi Apparatus located?
The Golgi apparatus is present in eukaryotic cells only (plant and animal cells). Animals have fewer, larger Golgi apparatus, while plant cells will have several hundred smaller versions. Mammalian cells typically contain hundreds of cisternae (pancake-stack like structures that make up the organelle), while less complex organisms such as protists typically contain much fewer cisternae.History of the Golgi Apparatus
Because the Golgi apparatus is amongst the largest organelles in cells, it was one of the first organelles to be discovered. The discovery of the Golgi complex occurred quite by accident. In 1898, a scientist by the name of Camillo Golgi identified the Golgi apparatus while researching spinal ganglion of the nervous system. In order to better see the tissue under a microscope, Golgi created a chromoargentic or “black” stain. When he applied this stain to the spinal ganglion, he saw a “reticular apparatus” that was stained black and determined that this must be a new organelle.
Unfortunately, because the technology of the time was so limited, scientists were skeptical of Golgi’s discovery. It wasn’t until the creation of the electron microscope in the 1930s that scientists confirmed that there indeed was a unique organelle, now called the Golgi apparatus.
Fun Facts:
- The Golgi apparatus is the only organelle to be named after a scientist.
- Despite it being nearly a century after the silver staining solution created by Golgi was used, scientists still do not understand the chemical mechanism behind the staining process.
Meet the Golgi Apparatus
While the endoplasmic reticulum and ribosomes are the organelles responsible for creating vital proteins, these proteins that are not ready to be used by an organism. Before the proteins can be sent off to different locations to perform their jobs, there is one organelle through which they must pass through first: the Golgi apparatus. The Golgi apparatus (or Golgi Complex, Golgi Body) is the organelle that sorts, modifies, packages, and ships proteins and lipids and proteins for secretion. It’s no wonder that the nickname of the Golgi apparatus is the “post office” of the cell! And if this weren’t enough, the Golgi apparatus helps create an important organelle in the cell used to degrade proteins, lipids, and more: lysosomes.
Note: Studying the Golgi apparatus helps us understand a major theme found in biology: biological systems interact, and these systems and their interactions pose complex properties, and more specifically, the structure and function of subcellular components, and their interactions, provide essential cellular processes. (Biology Big Idea #4)
Sources:
Golgi Apparatus (British Society for Cell Biology): http://bscb.org/learning-resources/softcell-e-learning/golgi-apparatus/
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