Question

What is a prion?

Short answer

Prions are misfolded proteins that cause infectious neurodegenerative diseases by inducing normal proteins to misfold.

Step-by-step solution

- Introduction to Prions

Prions are infectious agents composed entirely of a protein material. Unlike bacteria, viruses, fungi, and other pathogens, prions do not contain any genetic material (DNA or RNA).

- Understanding Protein Misfolding

Prions are misfolded versions of a normal protein found in the brain. This abnormal folding causes the normal proteins to convert into the prion form, leading to a chain reaction of misfolding.

- Diseases Caused by Prions

Prions cause a variety of neurodegenerative diseases, which are often fatal. Examples of prion diseases include Creutzfeldt-Jakob Disease (CJD) in humans, Bovine Spongiform Encephalopathy (mad cow disease) in cattle, and scrapie in sheep.

- Mechanism of Spread

Prions can spread through contaminated food, medical instruments, or inherited genetic mutations. The mechanism of prion propagation is unique because it involves the transmission of protein misfolding rather than genetic material.

Key concepts

Protein Misfolding

Prions are unique because they are all about protein misfolding. Normally, proteins fold into specific shapes that enable them to perform their functions. However, prions are proteins that have folded incorrectly. This abnormal folding not only makes the prion itself dysfunctional, but it also affects other normal proteins.
When a prion comes into contact with a normal protein, it can cause the normal protein to misfold into the prion shape. This creates a chain reaction where more and more proteins become misfolded. The accumulation of these misfolded proteins is harmful to cells, especially in the brain.
This chain reaction of misfolding is what makes prions so dangerous. Unlike viruses or bacteria, prions don’t replicate through genetic material. Instead, they corrupt the normal proteins to spread the misfolding.
This form of propagation is especially hard to stop because standard infection-fighting strategies, like antibiotics, do not work against protein misfolding.

Neurodegenerative Diseases

Prions cause severe neurodegenerative diseases. These are conditions that result in the progressive degeneration and death of neurons in the brain. Neurons are the cells responsible for transmitting information throughout the brain and body.
One well-known prion disease in humans is Creutzfeldt-Jakob Disease (CJD). Symptoms of CJD include memory loss, personality changes, and motor dysfunction. Unfortunately, it is always fatal.
In animals, prion diseases include Bovine Spongiform Encephalopathy (BSE), commonly known as mad cow disease, and scrapie in sheep. These diseases also lead to severe brain damage and are fatal.
Neurodegenerative diseases caused by prions are particularly devastating because they lack an effective cure. Once the prion infection starts, it rapidly progresses, severely impairing brain functions.

Infectious Agents

Unlike other infectious agents like bacteria, viruses, and fungi, prions don't carry any genetic material. Instead, they are infectious proteins.
Prions can spread in several ways. One common method is through contaminated food. For instance, humans can get CJD by eating beef infected with BSE. Prions can also spread through medical instruments that haven’t been properly sterilized.
Another way prions can spread is through inherited genetic mutations. Some people carry genes that make them more susceptible to prion diseases.
Because prions spread through misfolding rather than living replication, they present unique challenges for medical treatments. Current sterilization methods might not always eliminate prions because they are extremely resistant to traditional methods that kill bacteria and viruses.