## Core Concept
Prions are infectious proteins that cause fatal neurodegenerative diseases in animals, including humans. They are unique in that they do not contain nucleic acids (DNA or RNA), which are typically found in viruses, bacteria, and other infectious agents. The term "prion" stands for "proteinaceous infectious particle."

## Why the Correct Answer is Right
The correct answer, , indicates that prions are infectious proteins. This is accurate because prions are misfolded proteins that can induce normal proteins in the brain to also misfold, leading to brain damage and the characteristic symptoms of prion diseases, such as Creutzfeldt-Jakob disease in humans and Bovine Spongiform Encephalopathy (BSE or "mad cow disease") in cattle. The mechanism involves the conversion of the normal cellular prion protein (PrP^C) into an abnormal isoform (PrP^Sc), which aggregates and forms amyloid fibrils that accumulate in the brain.

## Why Each Wrong Option is Incorrect
* **Option A:** This option is incorrect because prions do not contain DNA.
* **Option B:** This option is incorrect because prions do not contain RNA.
* **Option D:** This option might suggest that prions are viruses or contain viral components, which is incorrect because prions are purely proteinaceous and do not contain nucleic acids.

## Clinical Pearl / High-Yield Fact
A key point to remember is that prion diseases are invariably fatal and have no known cure. They can be transmitted through contaminated food (as in the case of BSE), medical procedures (e.g., corneal transplants), or genetic inheritance. The diagnosis is often confirmed post-mortem by histopathological examination of brain tissue.

## Correct Answer: C. Infectious proteins.