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Prions

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by

Fariha Ruhullah

on 23 September 2012

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Transcript of Prions

Discovery Prions by Fariha, JAwadul &Labib In the 1960’s radiation biologist Tikvah Alpah and the mathematician John Stanley Griffith conjured up the hypothesis that there are some prion diseases, that were first caused by an infectious agent made fully of proteins. Soon enough, their theory worked to prove the discovery that this was the agent that caused the diseases scrapie and Creutzfelt-Jakob disease resisted ionizing radiation. It soon proved that this agent was too small to be a virus, and later on they named it ‘Prion’ DISCOVERY The main protein that the agent Prion (PrP) is made from is found in every living things body, no matter how healthy or alive they are. But, the PrP that is found in materials that are infectious has a different structure to those that are found in healthy humans and animal, and it is also resistant to proteases, one of the types of enzymes in the body that can break down the proteins. The common form of the protein is named PrPC, where as the infectious form is named PrPSc — The ‘C’ would refer to either cellular or common PrP, where as the Sc would refer to scrapie, a prion disease that is found in sheep. PrPc is naturally very well defined, but PrPSc is the opposite, being poorly defined. ISOFORMS PrPC is the common protein found in the membranes of the cell, in humans PrP has 209 Amino Acids. In general it has one disulfide bond, the molecular mass of 35-36 kDs, and what is called an alpha-helical structure. PrPC is digested by the serine protease Proteinase K. (PI-PLC). PrP is discovered to play very important roles in cell-to-cell adhesion, and may also be involved in the cell-to-cell communication that proceeds in the brain. PrP(C) The more infectious isoform of PrP, which is known as PrPSc, can convert the normal PrPC proteins into the infectious isoforms by completely changing their shape, which distorts the way cells connect. Mixes of these unusual isoforms work to create amyloid fibres, which create plaque. It is not sure if whether or not these mixes of isoforms are the cause of cell damage, or if they are just merely a side effect of the undergoing process of the disease. PrP(SC) Most studies assume that when a Prion replicates, they go through this procedure. Firsty a single Prpsc molecule will bind to the common PrpC molecule and then it undergoes its conversion into PrPsc. The two PrPsc molecules that are now there can come apart from each other and continue to replicate more PrPc molecules. PRION REPLICATION This particular hypothesis states that the TSEs that are caused by the replicates and informated molecule, which would most likely be nucleic acid, are PrP. Many TSEs, like scrapie, show detailed strains with very specific and complicated biological properties. PRION DISEASES Nobody really knows whether prions are the agent which causes the disease, or whether it is just a symptom that is caused by a different agent. The following sub-topics discuss this hypothesis: Some pertain to the following composition of the infectious agent (protein-only, protein with other components, virus, or other), while others to the mechanism of reproduction. DEBATE m It's been predicted that Prion diseases can be spread in a total of 3 different ways: acquired, familial, or sporadic. It's assumed by scientists and biologists that the diseased form comes into direct contact with the normal form to rearrange it's structure.
Ongoing research suggests that the infection of Prion diseases in animals is through ingestion. It is also thought that Prion diseases are spread through the environment through the remains of animals via Urine, saliva or any other body fluids. TRANSMISSION Prions are infections by their on effects on the common versions of the protein. To sterilize a prion it would have to distort the protein to such a state that the molecule it self would be incapable of folding the normal proteins. Prions are normally fairly resistant to such things as proteases, heat, radiation, and formalin treatments, although these such things would be necessary to reduce the effect of the disease. STERILIZATION When Prions were discovered it was that that all of the pathogens has used nucleic acids to commence with their replication.This "protein-only hypothesis" supports the fact that a protein structure is able to replicate without the use of nucleic acids. PROTEIN ONLY Prions are immune to cause diseases by mixing with other cells in the central nervous system to create plaque called 'amyloid', which distorts the common tissue structure. Prion diseases to tend to stay effective for a long time and once the symptoms appear the disease progresses quickly, possibly leading to fatal or brain injuries. The symptoms may include dementia, ataxia and behavioural or personality distortion. VIRAL HYPOTHESIS Despite all the effort that has been put into this hypothesis, notable titers of the ineffectual behavior of prions have never actually been produced by refolding the common PrP molecules, which raises the doubt about the truth behind the 'protein only hypothesis'. The protein only hypothesis also fails to provide us a scientific explanation as to why the prion has the ability to target specific areas of our brain. All of these are the reasons that have given rise to the 'multi-component' hypothesis. MULTI-COMPONENT GENETIC FACTORS The gene for the normal protein has been identified as: the PRNP gene. In all cases that have ever been found of the Prion diseases there is always a sort of mutation in the PRNP gene. They are many different mutations and they are probably to fold into an abnormal prion. Mutations can occur through out the gene. as of this year, there are 8 known types of the Prion protein that have been discovered in fungi. A prion has been found in the fungus names Podospora Anseria. The prions in this fungus behave in the same manner as PrP, but are subsequently non toxic to their hosts. FUNGI Thankyou for watching:)
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