Prions: Videos & Practice Problems

Prions are misfolded proteins that act as infectious agents, leading to neurodegenerative diseases. Unlike viruses and bacteria, prions lack nucleic acids and are composed solely of protein. The normal prion protein (PrPC) can be converted into the disease-causing form (PrPSc) through interactions with misfolded prions. This conversion results in the accumulation of PrPSc in neural tissue, causing spongiform encephalopathies. These are characterized by sponge-like lesions in the brain, leading to diseases such as Creutzfeldt-Jakob disease in humans and scrapie in animals. The accumulation of PrPSc disrupts normal cellular functions, ultimately causing cell death and tissue damage.

Prion diseases, also known as transmissible spongiform encephalopathies, affect both humans and animals. In humans, examples include Creutzfeldt-Jakob disease (CJD), fatal familial insomnia, and kuru. In animals, prion diseases include scrapie in sheep, mad cow disease (bovine spongiform encephalopathy) in cattle, and chronic wasting disease in deer and elk. These diseases are characterized by the accumulation of misfolded prion proteins in the brain, leading to neurodegeneration and the formation of sponge-like lesions in neural tissue.

Prions differ from viruses and viroids in their composition and mechanism of infection. Prions are composed solely of misfolded proteins, lacking any nucleic acids. In contrast, viruses contain proteins, nucleic acids (DNA or RNA), and sometimes lipids. Viroids are simpler than viruses, consisting only of a short strand of RNA without a protein coat. While viruses and viroids rely on their genetic material to replicate and cause infection, prions propagate by inducing normal proteins to misfold, leading to the accumulation of pathogenic prion proteins and subsequent neurodegenerative diseases.

Prion-induced neurodegeneration occurs through the conversion of normal prion proteins (PrPC) into the misfolded, disease-causing form (PrPSc). This conversion is initiated by the interaction between PrPSc and PrPC. The misfolded PrPSc induces the normal PrPC to adopt the abnormal conformation, leading to the accumulation of PrPSc in neural tissue. Over time, these misfolded proteins aggregate, forming clumps that disrupt cellular functions. The accumulation of PrPSc causes spongiform lesions, characterized by holes in the brain tissue, which impair neural function and lead to cell death, resulting in neurodegenerative diseases.

Spongiform encephalopathies are a group of neurodegenerative diseases characterized by sponge-like lesions in the brain. These lesions are caused by the accumulation of misfolded prion proteins (PrPSc) in neural tissue. The normal prion protein (PrPC) is converted into the disease-causing form (PrPSc) through interactions with existing misfolded prions. This conversion leads to the aggregation of PrPSc, forming clumps that disrupt normal cellular functions. The resulting tissue damage and cell death create the characteristic sponge-like appearance in the brain, leading to diseases such as Creutzfeldt-Jakob disease in humans and scrapie in animals.