Published by Australian Academy of Science
Activity 2 | Prions – morphing agents of disease

Distinguishing prions and viruses

1. BSE is thought to be caused by a prion. Explain in your own words what a prion is and how you think it differs from a virus.

2. Do you think prions are living things? Give reasons for your answer.

Teachers notes

1. Prions are twisted variants of certain kinds of normal proteins (these will be referred to as normal prion protein). Prions resist breakdown by proteases, and are infective because when a (twisted) prion comes in contact with normal prion protein it induces the normal prion protein to change its conformation to that of a twisted prion. The new (twisted) prion has the same effect on any similar normal prion protein it contacts, so the spread is rather like a domino effect.

   Prions differ from viruses in composition (prions consist of protein only whereas viruses exist as particles consisting of nucleic acid, usually with a protein coat) and in mode of replication.

2. Prions are not considered to be living because they do not have inputs and outputs, respond to stimuli or reproduce totally new copies of themselves.

   The existence of prions is now widely accepted. However, there are still some scientists who think that prions have nucleic acid associated with them. This would make them more like a type of virus. Sometimes the term 'sub-viral' is used to describe the agent causing spongiform encephalopathies.