The sulfating of substances passing through the lumen of Golgi body is carried out with the help of sulfotransferases. Golgi apparatus plays an important role in the prevention of destruction of cells or apoptosis. The Bcl-2 genes present in the Golgi are used for this purpose. Golgi Apparatus. Top Menu BiologyDiscussion. This is a question and answer forum for students, teachers and general visitors for exchanging articles, answers and notes.
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Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. We also use third-party cookies that help us analyze and understand how you use this website. These cookies will be stored in your browser only with your consent. You also have the option to opt-out of these cookies. The nature, and even existence, of this 'unconventional' secretion route is not universally agreed upon, and why only some proteins would be able to access such a route is unclear.
The evidence for unconventional secretion will become more robust if and when its specific machinery is identified - especially given that the principal protein claimed so far to be required for bypassing the Golgi, GRASP, is itself a Golgi resident with a well established role in cisternal stacking. Ah well. That is a rather embarrassing question. Although we know what arrives and departs, how proteins move from one side of the Golgi to the other has been debated for decades, and still is.
The original model from electron micrographs was that cisternae formed on the cis side, and then 'progressed' or 'matured' through the stack until they broke up at the trans side or fused with a pre-existing trans cisterna.
This was then challenged by the proposal that transport vesicles carry cargo forward through the stack. Although cisternal maturation is back in favor with most in the field, some recent papers have suggested that tubular connections form between cisternae to allow rapid forward movement of cargo. For a lucid account of the details of this long-running debate the interested reader is referred elsewhere see below.
It also remains to be seen if the nature of intra-Golgi transport has any implications for the way that the Golgi performs its fundamental roles for the cell. A particularly poorly understood aspect of the Golgi is the generation of the carriers that move from the trans Golgi to the plasma membrane.
Unlike other traffic steps, no coat proteins have been identified, and there may be redundant pathways to the plasma membrane, especially in polarized cell types such as epithelia and neurons where proteins need to be delivered to different parts of the cell surface.
Likewise, there appear to be multiple routes back to the Golgi from endosomes, but how many routes, what machinery acts for which, and where they arrive at the Golgi are not yet resolved. It's not. Another is the mechanism that ensures that the Golgi resident enzymes remain in the stack rather than departing with exiting cargo.
There is evidence that transmembrane domains can contribute to retention, but how different enzymes are targeted to different parts is not known, or even how the transmembrane domains act.
How the Golgi stack is assembled from individual cisternae is also not well understood, nor the purpose that is served by the stacked arrangement, given that it is not a universal feature of all Golgis.
Indeed, the issue of how and why the Golgi varies between organisms is also waiting to be resolved as more of the field explores species outside of the two kingdoms of lab life, yeast and HeLa cells.
However, the components and ubiquity of these contacts remain enigmatic. In mammalian cells, the Golgi ribbon and stacks fragment during mitosis to facilitate equal distribution between daughters, indicating that Golgi structure can be regulated. Finally there are the general issues of homeostasis and scaling that apply to all cellular structures as discussed recently in BMC Biology by Wallace Marshall.
In the case of the Golgi there must be homeostatic mechanisms underlying the stack's highly regular, if species-specific, size and shape. Max Planck argued that a scientific truth only triumphs when its opponents eventually die, but I believe that technological advances will save us from what would otherwise, I hope, be a long wait. In particular, recent advances in super-resolution microscopy hold the promise of clearly resolving the distribution of cargo, resident enzymes, and traffic machinery within individual cisternae, and even following this through time in living cells.
It can be hard to localize specific proteins in thick sections, but there has been exciting recent progress in studying frozen unfixed sections in which it may eventually be possible to recognize protein density corresponding to recently solved structures of trafficking components.
Ultimately, a molecular level understanding of mechanism will need to move beyond descriptive studies towards the biochemical reconstitution of Golgi function in vitro. This is a daunting challenge that few, if any, labs are currently embracing, but it may be that particular steps can be addressed in isolation as structural biologists have recently had considerable success expressing recombinant membrane transport components that will be invaluable for such in vitro assays.
Much of the molecular machinery of the Golgi was identified by biochemical assays and yeast genetics. More recently, genome-wide RNA interference screens in metazoan cells have identified a few further components that were missed or were absent from yeast. More unexpectedly, an increasing number of rare genetic diseases are being found to be caused by null alleles of genes encoding Golgi proteins.
It seems that the loss of some Golgi proteins that are ubiquitously expressed and well conserved in evolution results in defects that, although severe, are not cell lethal but instead specific for particular tissues or cargo proteins, or result in reduced levels of glycosylation.
This suggests that some Golgi machinery is not required for basic traffic but for ensuring that the organelle functions at maximum efficiency, especially when large amounts of material are being secreted. It is clear that much of the Golgi remains mysterious over years after its discovery, a reflection surely of its complexity rather than the quality of research in the field. Given its central role in membrane traffic and the increasing number of links to human disease, resolving these questions seems certain to open the door to a new understanding of fundamental mechanisms in eukaryotic biology.
J Cell Biol , Curr Opin Cell Biol , Cold Spring Harb Perspect Biol Lowe M: Structural organization of the Golgi apparatus. Marshall WF: Origins of cellular geometry. BMC Biol , 9: N Engl J Med , The Golgi is located right near the nucleus. It's called a perinuclear body, and it's actually right near the endoplasmic reticulum as well.
And when proteins come out of the endoplasmic reticulum, they go into the Golgi for further processing. For example, carbohydrates are put on some of the proteins, and then afterwards these glycoproteins--meaning they have carbohydrate as well as protein on them, these glycoproteins move out of the Golgi to the rest of the cell.
And they do so inside other vesicles.
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