Chapter 9 (4)

Question 1

Defective Viruses

Answer 1

Viruses that are parasitic on other viruses.

• Require other virus to provide some function.
• Some rely on intact virus of same type.
• Satellite viruses: defective viruses for which no intact version exists; rely on unrelated viruses as helpers.

Question 2

Viroids

Answer 2

Viroids: infectious RNA molecules that lack a protein.

• Smallest known pathogen
• Cause number of important plant diseases
• small, circular, ssRNA molecules
• do not encode proteins; completely dependent on host encoded enzymes

Question 3

Prions

Answer 3

Prions: infectious proteins whose extracellular form contains no nucleic acid.

• known to cause disease
• host cell contains healthy proteins
• prion misfiling results in neurological symptoms of disease.

Question 4

Prion Disease

Answer 4

Three mechanisms:

• -Infectious prion disease: pathogenic form of prion protein is transmitted between animals or humans.
• -Sporadic prion disease: random misfolding of a normal, healthy prion protein in an uninfected individual.
• -Inherited prion disease: mutation in prion gene yields a protein that changes more often into disease causing forms.