What are prions?

Prions are indeed infectious agents composed solely of protein that can lead to neurodegenerative diseases. They are unique because, unlike bacteria, viruses, or fungi, prions do not contain any nucleic acids (DNA or RNA). This unusual structure allows them to induce abnormal folding of normal cellular proteins, particularly in the brain, leading to a cascade of misfolding that causes cellular damage and disease. Prions are responsible for various conditions such as Creutzfeldt-Jakob disease, mad cow disease, and kuru, among others.

The other options describe different types of pathogens or genetic phenomena, but they do not accurately capture the nature of prions. For example, pathogens composed of RNA pertain to viral infections, while viral particles that infect bacteria refer to bacteriophages. Additionally, mutations of genetic material involve changes at the DNA or RNA level, which is unrelated to the protein-only structure of prions. This distinction is crucial for understanding the unique characteristics and implications of prion-related diseases.