Biology, Eighth Edition (Raven)

Chapter 27: Viruses

Prion Diseases

Why do the changes in proteins in a prion disease not require a change in DNA? Prions are malformed proteins. However the change is not a change in amino acid sequence but a change in conformation. The amino acid chains of prions are folded differently than the chains of the functional version of the molecule. When a prion interacts with a functional version of the protein it causes the conformation of the functional protein to change. The formerly functional protein changes its folding pattern to that of the prion. Both the original prion and the new prion can go on to change the conformation of other protein molecules. In this way the change can spread with no change in DNA.

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


1.	The abnormal form of the protein is designated

		A)	PrP^Abnormal.
		B)	PrP^S.
		C)	PrP^C.
		D)	PrP^Sc.
		E)	PrP^Cs.

2.	Prions are believed to cause _______ diseases.

		A)	respiratory
		B)	neurodegenerative
		C)	sexually-transmitted
		D)	digestive
		E)	plant

3.	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.

4.	Disease symptoms are believed to be the result of dense aggregates of the abnormal protein.

		A)	True
		B)	False

5.	In some inherited cases, the normal prion protein can convert spontaneously to the abnormal form, but at a slow rate.

		A)	True
		B)	False