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The word is derived from a combination of the words "proteinaceous infectious particle." It refers to the hypothesis (widely discounted when first proposed, but now generally accepted) that infectious agents causing such diseases consisted only of protein, with no nucleic acids. All pathogens known prior to that time (bacteria, viruses, etc.) contain nucleic acids, which enable reproduction. The prion hypothesis was developed to explain why the mysterious infectious agent causing Creutzfeldt-Jakob Disease resisted ultraviolet radiation (which breaks down nucleic acids) but responded to agents that disrupt proteins. |
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The word is derived from a combination of the words "proteinaceous infectious particle". It refers to the hypothesis (widely discounted when first proposed) that infectious agents causing such diseases consisted only of protein, with no nucleic acids. All pathogens known prior to that time (bacteria, viruses, etc.) contain nucleic acids, which enable reproduction. The prion hypothesis was developed to explain why the mysterious infectious agent causing Creutzfeldt-Jakob Disease resisted ultraviolet radiation (which breaks down nucleic acids) but responded to agents that disrupt proteins. |
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A breakthrough occurred when researchers discovered that the infectious agent consisted mainly of a protein called PRP. This protein was similar to another that is found in the membranes of normal cells (the precise function of which is not known), but the infectious agent was distinguished by an altered shape. It is hypothesized that the distorted protein binds to normal proteins of the same type and somehow induces them to change their shape as well, producing a chain reaction that both propagates the disease and generates new infectious material. Since the original hypothesis was proposed, a gene for the PRP protein has been isolated, the mutation that causes the variant shape has been identified and successfully cloned, and studies using genetically altered mice have bolstered the prion hypothesis. The evidence in support of the hypothesis is quite strong now, but not incontrovertible. |
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A breakthrough occurred when researchers discovered that the infectious agent consisted mainly of a protein called PRP. This protein is found in the membranes of normal cells (its precise function is not known), but the infectious agent was distinguished by an altered shape. It is hypothesized that the distorted protein binds to normal proteins of the same type and somehow induces them to change their shape as well, producing a chain reaction that both propagates the disease and generates new infectious material. Since the original hypothesis was proposed, a gene for the PRP protein has been isolated, the mutation that causes the variant shape has been identified and successfully cloned, and studies using genetically altered mice have bolstered the prion hypothesis. The evidence in support of the hypothesis is quite strong now, but not incontrovertible. |
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Not all prions are dangerous, in fact they are found naturally in many (perhaps all) plants and animals. Because of this, scientists reasoned that the deformed proteins must give some sort of evolutionary advantage to their host. This was proved to be the case when studying a specific type of moss covering forest floors. Normally viruses can travel from an infected moss section to an uninfected moss section when the areas grow close enough for the outer cells to touch. However prions were discovered in the infected moss, which appeared to travel part way in to the sides of the uninfected moss. This caused cells on the edges of the moss to die, creating a barrier of dead cells which the virus was not able to cross. Prions have also been speculatively linked to the differentiation? process, which causes embyronic cells to specialise in to specific tissue (such as muscle or blood cells). |
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Not all prions are dangerous; in fact they are found naturally in many (perhaps all) plants and animals. Because of this, scientists reasoned that the deformed proteins must give some sort of evolutionary advantage to their host. This was proved to be the case when studying a specific type of moss covering forest floors. Normally viruses can travel from an infected moss section to an uninfected moss section when the areas grow close enough for the outer cells to touch. However prions were discovered in the infected moss, which appeared to travel part way in to the sides of the uninfected moss. This caused cells on the edges of the moss to die, creating a barrier of dead cells which viruses are unable to cross, preventing contamination. Prions have also been speculatively linked to the differentiation? process, which causes embyronic cells to specialize into specific tissues (such as muscle or blood cells). |
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The reason that prions are not detected by the immune system is that their 'safe' form is already present from birth in the body, the only distinction the 'dangerous' prions having is that they are folded slightly differently. Prions infect the nerve lining of neural cells, froming an aggregate which ultimately destroys nerve cells. Depending on the area of the brain which they infect the symptons can be different. For example infecting the cerebellum causes impairment of movement. Infecting the cerebul cortex results in a decrease in memory and mental agility. |
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The reason prions are not detected by the immune system is that their "safe" form is already present from birth in the body. The only distinction the "dangerous" prions have is that they are folded slightly differently. Prions infect the nerve lining of neural cells, froming an aggregate which ultimately destroys nerve cells. Depending on the area of the brain which they infect the symptons can be different. For example infecting the cerebellum causes impairment of movement. Infecting the cerebral cortex results in a decrease in memory and mental agility. |
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These diseases are known to be caused by prions: |
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These diseases are now believed to be caused by prions: |
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