Prions: Study with Video Lessons, Practice Problems & Examples

Prions, or proteinaceous infectious agents, are misfolded proteins that can induce normal proteins to misfold, leading to neurodegenerative diseases such as Creutzfeldt-Jakob disease and scrapie. The misfolded form, PRP_Sc, interacts with the normal PRP_C protein, causing its conversion and accumulation, resulting in spongiform encephalopathies characterized by sponge-like brain lesions. Understanding prion behavior is crucial for grasping their role in disease pathology and transmission.

Prions

This video we're going to begin our lesson on prions. And so first we need to recall from some of our previous lesson videos that the term prions is actually derived from proteinaceous infectious agents. And so you can see the p r, the I n, and so those are also found, here in prions. And so, these prions or proteinaceous infectious agents, like viruses and viroids, are also acellular obligate intracellular parasites. However, unlike viruses, which are made of proteins, nucleic acids, and sometimes lipids, and viroids, which are only made of RNA, prions, as their name implies with the proteinaceous part, are only made of misfolded proteins. Now these prions can actually cause normal proteins to misfold, which can ultimately lead to some type of neurodegenerative disease. And so, notice down below over here on the left hand side of our image, we're showing you some prion diseases or diseases caused by prions in humans, such as Creutzfeldt-Jakob disease, family fatal insomnia, and kuru, and then also some prion diseases that cause disease in animals such as scrapie, mad cow syndrome, and chronic wasting disease. Now these prions can ultimately accumulate in neural tissue such as for example the brain and they can cause what are known as transmissible spongiform encephalopathies. And so these transmissible spongiform encephalopathies are really when brain tissue deteriorates forming holes and a sponge-like appearance in the brain. And so if we take a look at our image down below, notice on the left hand side over here, what we're showing you is a micrograph of a normal brain, of normal brain cells. And on the right over here what we're showing you is a brain with spongiform encephalopathies. And so what you'll notice is the brain with spongiform encephalopathies has these spongiform lesions, basically these holes, and, it is deteriorating. And all of these holes, these gaps that you see here, this is what gives the brain a sponge-like appearance, which is where it gets its name, spongiform encephalopathies. And so, ultimately, again, these are going to be associated with prion formation and can, lead to these degenerative diseases that we have here. And so this here concludes our brief introduction to prions, and we'll be able to talk a little bit more about prions as we move forward in our course. And so I'll see you all in our next video.

Prion Development in Neurons Leads to Scrapie

This video, we're going to be talking about the prion development in neurons leading to the disease scrapie in animals. And so the infectious prion protein that is misfolded leading to the disease scrapie is PrP^Sc, which is really just an abbreviation for prion protein scrapie. And the normal form of that prion is actually PrP^C, which is prion protein cellular, and so PrP^C is the normal protein with normal function, and PrP^Sc is the prion that leads to the disease scrapie. And so the accumulation of the PrP^Sc, the prion form, in the brain is attributed to its interaction with the normal protein, which is once again PrP^C. And so the interaction PrP^C. And so the interaction between PrP^Sc, the prion, and the normal protein, PrP^C, is going to cause the normal protein, PrP^C, to misfold. And if the PrP^C protein misfolds, it is going to result in a PrP^Sc prion. And so the PrP^Sc prion will accumulate over time through interacting with PrP^C and converting the PrP^C to PrP^Sc. And so, PrP^Sc accumulates and begins to aggregate in the brain leading to spongiform encephalitis and the disease scrapie in animals.

And so, if we take a look at our image down below we can get a better understanding of the prion development in neuron cells and how that results in the neurological disease scrapie in animals. And so notice on the far left over here we're taking a look inside of a neuron, which is a type of cell of the nervous system, a cell that can be found in the brain. And so inside the neuron there can be, PrP^C, which is the normal functioning protein with the correct shape, but if there is a prion, it will be PrP^Sc. And so if they're both present in a neuron cell, what can happen is the PrP^Sc can interact with the PrP^C. And so the misfolded PrP^Sc prion protein can interact with the normal PrP^C protein. And so the misfolded PrP^Sc prion can convert the normal PrP^C into PrP^Sc. And so notice that the PrP^Sc is accumulating, and so it can continue to interact with other normal PrP^C proteins and the continued conversion as PrP^C PrP^Sc accumulates. And so the accumulation of PrP^Sc is going to lead to the aggregation or PrP^Sc aggregation, or clumping as you see like that and ultimately that clumping can lead to causing spongiform lesions which are those holes that you can find in brain tissue, and that leads to the disease scrapie in animals.

And so really these prions once again are just misfolded proteins that can interact with normal proteins and cause the normal proteins to also misfold and become prions. And so this here concludes our brief lesson on prion development and neurons leading to the disease scrapie and we'll be able to get some practice applying these concepts as we move forward in our course and so I'll see you all in our next video.

What are prions?

• A. Mobile segments of DNA.
• B. Tiny circular molecules of RNA that can infect plants.
• C. Viral DNA that attaches itself to the host genome and causes disease.
• D. Misfolded versions of normal proteins that can cause disease.

Which of the following is true of prions?

• A. They can be inactivated by boiling at 100 °C.
• B. They contain a capsid.
• C. They are a rogue form of protein, PrP.
• D. They can be reliably inactivated by an autoclave.

Viroids and prions are both infectious agents. All of the following are major differences between viroids and prions except which of these answers?

• A. Viroids are only known to infect plant cells while prions are known to infect plant and animal cells.
• B. Viroids cause the misfolding of the host cell's proteins while prions block the host cell's expression of genes.
• C. Viroids are nucleic acid molecules while prions are composed of polypeptide chains.
• D. Viroids require the host's RNA polymerase to replicate while prions replicate by transforming the host cell's proteins.

Mad cow disease is a prion disease found in cattle. Why are prion diseases in meat a big concern?

• A. Prions cannot be destroyed by cooking meat.
• B. Prions cannot be destroyed with irradiation of meat.
• C. Prions are the most difficult infectious agent to deactivate or denature.
• D. There are no cures for prion diseases.
• E. All of the above.

Here’s what students ask on this topic:

What are prions and how do they cause disease?

Prions, or proteinaceous infectious agents, are misfolded proteins that can induce normal proteins to misfold. Unlike viruses and viroids, prions are solely composed of proteins. The misfolded form, PRP_Sc, interacts with the normal PRP_C protein, causing its conversion into more PRP_Sc. This accumulation leads to neurodegenerative diseases such as Creutzfeldt-Jakob disease and scrapie. The misfolded proteins aggregate in neural tissue, forming spongiform encephalopathies characterized by sponge-like brain lesions. These lesions result in brain tissue deterioration, leading to severe neurological symptoms and ultimately death.

What are some examples of prion diseases in humans and animals?

Prion diseases in humans include Creutzfeldt-Jakob disease, 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 spongiform lesions, which give the brain a sponge-like appearance.

How do prions differ from viruses and viroids?

Prions differ from viruses and viroids in their composition and structure. Prions are solely composed of misfolded proteins, whereas viruses are made of proteins, nucleic acids, and sometimes lipids. Viroids, on the other hand, are composed only of RNA. Unlike viruses and viroids, prions do not contain any genetic material. Prions cause disease by inducing normal proteins to misfold, leading to neurodegenerative conditions, while viruses and viroids replicate using the host's cellular machinery.

What is the mechanism of prion propagation in the brain?

The mechanism of prion propagation involves the interaction between the misfolded prion protein (PRP_Sc) and the normal cellular prion protein (PRP_C). When PRP_Sc comes into contact with PRP_C, it induces the normal protein to misfold into the prion form. This newly formed PRP_Sc can then interact with more PRP_C proteins, causing a chain reaction. Over time, the accumulation of PRP_Sc leads to the formation of aggregates and spongiform lesions in the brain, resulting in neurodegenerative diseases.

What are transmissible spongiform encephalopathies (TSEs)?

Transmissible spongiform encephalopathies (TSEs) are a group of neurodegenerative diseases caused by prions. They are characterized by the accumulation of misfolded prion proteins in the brain, leading to the formation of sponge-like lesions. Examples of TSEs include Creutzfeldt-Jakob disease in humans, scrapie in sheep, and mad cow disease in cattle. These diseases are transmissible, meaning they can be spread from one individual to another, often through contaminated food or medical procedures. TSEs are invariably fatal and currently have no cure.