Prions, short for proteinaceous infectious agents, are unique infectious agents composed solely of proteins. Unlike viruses and viroids, which are also obligate intracellular parasites, prions do not contain any nucleic acids; they are entirely made up of misfolded proteins. This misfolding is critical because prions can induce normal proteins in the body to misfold as well, leading to a cascade of dysfunction.

The misfolded proteins lose their normal function, which can result in severe neurodegenerative diseases. Notable examples of prion-related diseases include scrapie in sheep and mad cow disease in cattle. The structural differences between normal proteins and prions are significant; the misfolded prion proteins adopt an abnormal shape that disrupts normal cellular processes.

In a healthy brain, proteins maintain their proper structure, allowing them to function correctly. However, when prions are present, they can convert these normal proteins into misfolded versions, ultimately leading to a diseased state. This transformation is visually represented by comparing the structure of a normal protein with that of a prion, highlighting the critical role that protein conformation plays in cellular health.

Understanding prions is essential as they represent a unique class of infectious agents that challenge traditional concepts of disease causation, emphasizing the importance of protein structure in biological function.