Biology, Eighth Edition (Raven)

Chapter 27: Viruses

How Prions Arise

Why is the fact that a prion causes an infectious disease so surprising? Almost all infectious diseases are caused either by cellular organisms (prokaryotes or eukaryotes) or by viruses. All of these entities have DNA and/or RNA. They are either capable of directly reproducing themselves or, in the case of viruses, they can use cells to reproduce. Normally an infection requires reproduction. The disease causing entity (pathogen) needs to reproduce in order to spread to new hosts and multiply inside a single host. A single bacterium or virus is not likely to produce any symptoms in a host.

Prions are malformed proteins. Proteins are not capable of reproduction. They do not make copies of themselves. Prions are no exception to this statement. They do not reproduce. Instead they appear to cause normal versions of the protein to change conformation to the malformed version. The cells of the infected organism produce the protein which is then altered by the prions.

View the animation below, then complete the quiz to test your knowledge of the concept.


Which of the following diseases is(are) caused by prions?
A)mad cow disease
B)Creutzfeldt-Jacob disease in humans
C)scrapie disease in sheep
D)A and B
E)A, B, and C

The normal prion protein is
A)bound to the ribosomes of neurons.
B)bound to the cell membrane of neurons.
C)found in the nucleus of neurons.
D)found in the mitochondria of neurons.
E)found in the synapse between neurons.

A harmless PrP is converted into the infective PrP
A)only as a result of a mutation in the normal gene.
B)by a virus which binds to the normal protein and causes it to become misfolded.
C)by an abnormal PrP which binds to the normal protein and causes it to become misfolded.
D)by enzymes that break off parts of the harmless protein.
E)by interaction of a PrP from one species with that of a second species.

The gene for the prion protein has been found in vertebrates but not invertebrates.

The abnormal form of the protein is called PrPSc.
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