What describes infectious protein particles that lack a genome?

The correct answer is prions, which are indeed infectious protein particles that do not contain any nucleic acids, such as DNA or RNA. Prions are unique in the realm of infectious agents because they consist solely of protein. They cause disease by inducing abnormal folding of adjacent normal proteins in the brain, leading to neurodegenerative conditions. This characteristic distinguishes prions from viruses, which possess genetic material (either DNA or RNA) and rely on a host's cellular machinery to replicate.

In contrast, bacteria are single-celled organisms that have both DNA and the capability to reproduce independently. Fungi are also cellular eukaryotes with their own genetic material. Viruses, while capable of causing infections, also contain genetic material and need a host cell to propagate, which is why they do not fit the description of infectious protein particles lacking a genome. Prions' protein-only composition highlights a distinct category of infectious agents that operate differently from conventional pathogens like bacteria and viruses.