Final answer:
Prions are infectious agents made up of a single protein known as PrP or prion protein. They cause spongiform encephalopathies by converting the normal form of the protein (PrPC) into an infectious form (PrPSC), which aggregates and leads to brain damage.
Step-by-step explanation:
Prions are composed of a single protein called PrP, which stands for prion protein. Prions exist in two forms: the cellular form PrPC, and the infectious form PrPSC. When PrPSC is introduced into the body, it binds to PrPC and converts it into more PrPSC, resulting in a chain reaction. These misfolded proteins aggregate and lead to the brain damage seen in spongiform encephalopathies like kuru and BSE. Prions are a unique type of infectious agent since they do not contain DNA or RNA.