I understand that prions are folded proteins that cause infectious diseases in the brains of mammals.
**Some questions on top of the **
1. So don’t eat mammal brains in case of prions – does this mean all mammals have prions in their brains?
2. If I ate a mammal brain and got a prion disease, is it possible that that mammal doesn’t have the disease?
3. Is it the prions themselves that are infectious, or the diseases they cause that are?
4. How do the prions cause the diseases?
In: Biology
Some information for you, probably not complete answers but it’s a start:
> If I ate a mammal brain and got a prion disease, is it possible that that mammal doesn’t have the disease?
It’s possible (probable) that the mammal wasn’t showing symptoms yet when it was slaughtered. If it had been, it probably wouldn’t have been able to be used for meat anyway. Prion diseases tend to have very long incubation periods.
> Is it the prions themselves that are infectious, or the diseases they cause that are?
The disease. That’s less about prions and more about what “infectious” means in general.
> How do the prions cause the diseases?
Prions are able to convert “properly” folded proteins into improperly folded ones. As I understand it, we don’t really know how or why this happens.
Disclaimer: this is a very ELI5 explanation, glossing over several nuances.
Proteins are a long chain of amino acids. Think of each amino acid as having a slightly different magnetic pull in slightly different areas. This combination of magnetic forces “folds” the protein into a very VERY specific shape. This VERY specific shape is what allows the protein to do its job in the body. If a protein is “misfolded”, then it can’t do it’s job properly. If a protein can’t do its job, that can cause disease.
Prions are proteins that are not just misfolded, but are misfolded in such a way as to cause other NORMAL proteins to ALSO become misfolded. Think of bringing another magnet next to your very-specifically-folded magnetic chain.
Prions specifically affect proteins that do their job in the brain. Not all animals have prions, but unless the animal is exhibiting signs of disease, we don’t know if they do or not, so best not to risk it. Unlike most food-borne illnesses, prions are NOT destroyed by cooking. Thus it’s safer to just say “don’t eat brains.”
1. No, but all the prion badness we know of lives in the brain (and other neural tissues), so when it happens that’s where it coming from. It’s generally just not worth the risk, especially since we don’t have a good way to fight the infection once it’s happened.
2. It’s unlikely. You could spontaneously gain the disease through something like genetic mutation, in which case your disease is unrelated to you dining on brains, but it’s more likely you got the disease from eating a diseased brain (or similar infected protein-type stuff).
3. The prions themselves (though there’s been some research that implies some bacteria might be involved too, in at least some cases).
4. A prion is a protein that’s folded wrong – but it’s folded wrong in just the right way to cause other proteins to get folded wrong, too. We’re still figuring out exactly why this happens in practice, but imagine if you had a box of paperclips, and one of them was so bent out of shape that it was starting to mangle the other, otherwise-normal paperclips. All those mis-folded proteins start causing Problems™, most notably lots of tiny holes in whatever those proteins were a part of.
Proteins are sequences of smaller chemical blocks (called “amino acids”). The order of these blocks matters a LOT, because they can interact with each other in a lot of special, and VERY complicated, ways. These interactions define how the protein “folds” once it is made. The way a protein is folded is what causes that protein to do the chemical things it does. (This is also why cooking causes proteins to break down: you add enough energy to partly un-fold the proteins.)
Sometimes, proteins can fold incorrectly, which makes them not work right anymore. Usually, this doesn’t matter and the creature’s body will just break the defective protein down to build something else. Unfortunately, in very rare cases, some proteins fold wrong and it causes problems–the new way it’s folded up does bad things to the cells it’s in. Prions are proteins that have a special, *extremely* bad wrong folding, which doesn’t just cause problems by itself–it actually can make OTHER copies of that protein *change* into the wrong version.
When this happens to an essential protein, it can destroy cells and ruin organs. It just happens to be the case that one particular prion is a protein that is essential for brain cells to have the structure they need. The prion version of that protein breaks that structure. When you look at the brain tissue under a microscope, it looks like it’s full of holes. This is why the official name for “mad cow disease” is “bovine spongiform encephalopathy” — literally “sponge-like cow brain disease.”
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