Prion is a?
**Core Concept**
Prions are infectious proteins that cause fatal neurodegenerative diseases in animals, including humans. They are unique in that they do not require a nucleic acid component to replicate and cause disease. Prions are composed entirely of protein, which folds into a pathogenic conformation that can induce normal protein molecules to misfold and aggregate.
**Why the Correct Answer is Right**
Prions are a type of infectious agent that can cause diseases such as Creutzfeldt-Jakob disease (CJD) in humans, bovine spongiform encephalopathy (BSE) in cattle, and scrapie in sheep. They are resistant to heat, radiation, and disinfectants, making them difficult to inactivate. The prion protein (PrP) is the primary component of prions, and it is thought to be involved in the transmission of prion diseases. The misfolded prion protein (PrP^Sc) is the pathogenic form that causes disease, while the normal prion protein (PrP^C) is the cellular form that is converted to the pathogenic form.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because prions are not viruses, which require nucleic acids to replicate and cause disease.
**Option B:** Incorrect because prions are not bacteria, which are prokaryotic cells that require a cell wall and other cellular components to survive.
**Option C:** Incorrect because prions are not fungi, which are eukaryotic organisms that require a nucleus and other cellular components to survive.
**Clinical Pearl / High-Yield Fact**
Prions are highly resistant to inactivation and can survive autoclaving, making them a significant concern for laboratory safety. Handling prions requires specialized equipment and protocols to prevent transmission of disease.
**Correct Answer:** D. Infectious proteins.