For example, mad cow disease in cattle and screeping sheep is caused by these prion molecules. In fact, in humans a disease known as crytesval yaka disease which is a deadly disease. It's called by prion molecules. So what exactly is a prion and what are some properties of prions? Well, prions are these aggregate, these collection of proteins which normally exist in our body but which have misfolded. And because they misfolded, they form these insoluble aggregates.