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Some Prions May Be Helpful
An anonymous reader writes "Sciencentral has an article saying that many prions, far from causing
Creutzfeldt-Jakob Disease are actually responsible for long-term memory storage."
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You don't seem to know what a 'theory' is. All science is based on theory. Cells are a theory, gravity is a theory, hydrogen is a theory. So, of course, prions are a theory. How widely accepted the theory is, I don't know, but it's definately a theory.
Squids have giant axons, too--they were used for all the early studies of how neurons work because they're big enough to get electrode into.
The textbook theory is that molluscs did not evolved the myelin sheath. Without myelin sheaths, propagation speed is proportional to axon diameter. Thus molluscs that need rapid propagation speed do so by having big neurons.
"How to Do Nothing," kids activities, back in print!
Chaperones are proteins that help other proteins fold through protein-protein interactions. They're very common in mammalian cells and are also used as sensors for heat shock or other environmental stresses that cause widespread protein denaturing.
A prion is a protein that can induce a conformational change in the structure of a molecule of its own type. It's called an autocatalytic reaction.
So you might get something like
Prion-inactivated + Prion-activated --> 2 Prion-activated.
The hypthesis is that the fibers responsible for Alziehmers form as the prions become activated and polymerize. The fibers then disrupt the synapses between neurons.
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Well, to be completely anal about this (this is slashdot, after all), cells and hydrogen are not theories. Cell theory describes how various eucaryote (sp?) life forms function on this planet, and hydrogen is simply an element with an atomic number of 1. A theory in science is not a "wild-assed guess." It is an explanation for the mechanism behind some natural phenomenom, backed up by large enough body of evidence that allows most scientists to grant it temporary assent. Part of that assent implies that it provides predictions for other phenomena that are later verified.
An hypothesis may eventually become a theory, once enough evidence supporting that hypothesis has been accumulated, but theories never become laws. The law of gravity is the F=G*m1*m1*m2*m2/(d*d) equation that you see in first semester physics class. The theory of gravity describes why the law is they way it is.
Forgetting how to feed yourself contributes to death.
Remember, we use our brain for things occasionally. Sometimes, they are important.
Not pretty to watch someone going down the tubes with Alzheimer's. Pretty harrowing actually watching someone become a shell.
- Zav - Imagine a Beowulf cluster of insensitive clods...
Before Prusiner put forth his prion theory, slow acting viruses were thought to be responsible for infectious neurodegenerative diseases like kuru and scrapie. Prusiner demonstrated, however, that an extract of brain matter from a scrapie-infected animal, treated so as to disrupt nucleic acids but not denature proteins (thus eliminating bacteria and viruses as possible infectious agents) if injected in a healthy animal, could produce a scrapie-like disease in it. Thus, it was concluded that protein itself could act as an infectious agent. The mechanism by which this occurs is still not known for certain (hence, controversy), but the general theoretical outline is that an ingested prion is taken up by neurons, which do not recognize it as a dangerous foreign entity because they have the normal of the protein on their surface already, and incorrectly assume the prion to be more of the same. The misfolded prion protein has two fatal qualities: it can induce normal prion proteins on the neuron to flip themselves to the alternate misfolded form, and it's darn near indestructible. In particular, one theory about how prions specifically cause damage is that once your neurons realize they now have all this useless prion protein floating around, they target it for degradation in the lysosomes, cell organelles that contain an acidic pH and enzymes that catalyze protein breakdown. Unfortunately, the misfolded form seems to be highly resistant to acidic conditions and degradation by proteases (and coincidentally very heat tolerant- they withstand meat cooking temperatures, and even autoclaving), so prions clog up the lysosomes and cause them to burst, killing the neuron and spreading prions to other neurons. The destruction of neurons adds up to produce holes in the brain, giving the spongiform appearance characteristic of the disease.
There are some unanswered questions regarding the infectious nature of prions, including whether they are able to induce other prions to change conformation themselves versus receiving help from other proteins, and the role normal, healthy form prions play in the cell (initial studies suggested it played no known role, and that individuals with the gene for prion production turned off were highly resistant to transmissible prion infections, but other studies suggest prions are necessary for normal neurological function). here are also questions surrounding the role genetics plays in the disease- until it was linked to prions, CJD was considered a genetic disease, and it is believed that some individuals possess a mutated form of the prion gene that makes them more susceptible to both naturally acquired and tainted beef acquired forms of CJD. Also, variants of the same protein, PrP, have been implicated in every known prion disorder- kuru, CJD, nvCJD, FFI, GSS, scrapie, BSE- and these, while having a general pattern of brain destruction, loss of motor coordination, and eventual horrible death, are very different dieases that a focused in different areas of the brain, have different symptoms, and work on drastically different timescales. How is one protein responsible for all of these, and what is responsible for the d
"FDA staff reviewers expressed concern about the number of patients who were left out of the study because they died."