**Question:** Prions are killed by -

**Core Concept:** Prions are misfolded proteins that cause transmissible spongiform encephalopathies (TSEs) such as Creutzfeldt-Jakob disease (CJD), scrapie, and bovine spongiform encephalopathy (BSE). Prion protein (PrP) is a normal cellular protein, but in the disease state, it aggregates and forms Prion Protein Aggregates (PrAs).

**Why the Correct Answer is Right:**

Correct Answer: **D. Heat**

Heat treatment is effective in killing prions because it denatures and disrupts the Prion Protein Aggregates (PrAs) formed due to misfolding of the normal Prion Protein (PrP). Heat denatures the abnormal PrAs, preventing the propagation of the Prion Infection Cycle (PIC). In contrast, other methods such as chemicals, radiation, and freezing do not effectively eliminate prions due to their resistance to these interventions.

**Why Each Wrong Option is Incorrect:**

A. **Chemicals:** Prions are resistant to common chemicals like detergents, alcohol, and detergents. The PIC is not interrupted, leading to persistent prion infection.

B. **Radiation:** Prions have low water solubility, making them resistant to gamma radiation and other forms of radiation. The PIC is not interrupted, leading to persistent prion infection.

C. **Freezing:** Prions can survive freezing and thawing processes, as they are not influenced by temperature changes. The PIC is not interrupted, leading to persistent prion infection.

**Clinical Pearl / High-Yield Fact:**

Heat treatment, specifically at high temperatures (100-120°C) for an extended period (hours to days), is the most effective method for destroying prions in tissues and products derived from infected animals. This ensures the safety of food products and limits the spread of prion-related diseases in humans and animals.

**Correct Answer Explanation:**

D. **Heat:** Heat treatment effectively destroys prions by denaturing and disrupting the Prion Protein Aggregates (PrAs). Denaturation occurs when proteins lose their native structure and form new, non-functional molecules. The high temperatures (100-120°C) and prolonged exposure (hours to days) cause the denaturation and disruption of PrAs, interrupting the Prion Infection Cycle (PIC) and preventing the propagation of prion infections.