What is a characteristic feature of a prion?

A characteristic feature of a prion is that it is an abnormally folded protein. Prions are unique infectious agents that are primarily composed of protein. Unlike viruses or bacteria, which can contain nucleic acids (like DNA or RNA), prions do not have any genetic material. Their pathogenicity comes from the misfolding of normal proteins into a misfolded form that can induce other normally folded proteins to also adopt the misfolded shape. This leads to a cascade of misfolded proteins that accumulate in the brain, resulting in neurodegenerative diseases such as Creutzfeldt-Jakob disease and BSE (mad cow disease).

The nature of prions as proteins distinguishes them from other infectious agents, such as those represented by other answer choices, which involve nucleic acids or cellular structures. This abnormal protein folding mechanism is crucial for their function and impact on biological systems, making the correct choice reflect the fundamental understanding of prions.