Prion

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A prion is an infectious protein. It is the only infectious agent that contains no nucleic acids (such as DNA or RNA).

Prions are proteins that in their normal form are made of amino acids that are in a mainly α-helix structure. This form is known as PrPC.[1]

The normal form is found in cell membranes and thought to be involved in maintaining long term memories in the hippocampus.[2]

The abnormal disease causing form is the result of a misfolded protein PrPSc, in this form much of the structure is replaced by β-sheets.[3]

which combines to form helical fibres called amyloid. Amyloid fibres grow at the ends of proteins and as normal protein subunits bind to these ends they misfold and become a part of the amyloid[4]. This is why prions are classed as infectious agents. 

Prions occur in a multitude of organisms including humans. They are responsible for may neurodegenerative diseases and all prions found in mammals affect the brain or any other type of neural tissue. All diseases caused by prions are currently untreatable and result in the death of the affected individual[5]. An example of a disease that is caused by infectious prions is BSE (bovine spongiform encephalopathy), which is also known as mad cow disease[6]. This degenerative disease occurs in humans when they eat a part of an infected cow. 

References

  1. Naish, J., Court, D.S. and Revest, P. (2009) Medical Sciences. Elsevier Health Sciences UK. 239.
  2. Naish, J., Court, D.S. and Revest, P. (2009) Medical Sciences. Elsevier Health Sciences UK. 239.
  3. Naish, J., Court, D.S. and Revest, P. (2009) Medical Sciences. Elsevier Health Sciences UK. 239.
  4. Alberts, B Johnson, A Lewis, J Raff, M Roberts, K Walter, P (2008). Molecular Biology of the Cell. 5th ed. New York: Garland Science. 1499.
  5. Prusiner SB (1998). "Prions". Proceedings of the National Academy of Sciences of the United States of America 95 (23): 13363–83.
  6. Alberts, B Johnson, A Lewis, J Raff, M Roberts, K Walter, P (2008). Molecular Biology of the Cell. 5th ed. New York: Garland Science. 1498.
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