Tara Smith posted Entry 2417 on June 29, 2006 02:15 PM.
Trackback URL: http://www.pandasthumb.org/cgi-bin/mt/mt-tb.fcgi/2412

Last fall, Andrea wrote an excellent piece on prions, and how they “contradict century-old biological assumptions and seem to defy the expectations of Darwinian evolutionary theory.” He gives an overview of prions and discusses their potential role in heredity. My interest in them, of course, comes from the diseases they cause. Over at Aetiology, I have a post up discussing a new Lancet paper on the prion disease, kuru, and its potential to act as a model for other human prion diseases (such as “mad cow”). The authors suggest two things: one, that the incubation period of so-called “mad cow” disease may be longer than previously thought, and two, that there may be “waves” of epidemic, determined partly by host genetics.

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Comment #109342

Posted by 'Rev Dr' Lenny Flank on June 29, 2006 6:19 PM (e)

I’m curious — are there any indications that prions, when they reproduce, are capable of changing and then reproducing those changes?

Comment #109353

Posted by Gary Hurd on June 29, 2006 6:35 PM (e)

Kuru was a fascinating problem. Back in the ’70s Kuru was presented as either a “cultural phychosis” or as a “damnation of cannibalism.”

Of course it was transmitted by traditional funeral practices.

Comment #109363

Posted by Coin on June 29, 2006 7:48 PM (e)

This confused me at first, since I had never heard of Kuru and thought at first that you were talking about Koro.

Comment #109376

Posted by Christopher on June 29, 2006 9:31 PM (e)

Are there still some that maintain that prions do not contain a nucleic acid genome?

Comment #109378

Posted by Andrew McClure on June 29, 2006 9:49 PM (e)

Cristopher wrote:

Are there still some that maintain that prions do not contain a nucleic acid genome?

Are there some that maintain that prions do contain a nucleic acid genome?

This is from the Andrea Bottaro article linked at the top of this page:

Prions are unlike any other infectious agent in that they seem to have no nucleic acids at all. Indeed, after a long controversy, most scientists currently agree that prions propagate entirely as alternatively folded forms of certain proteins, through a mechanism that resembles crystal nucleation

Comment #109386

Posted by Andrea Bottaro on June 29, 2006 10:54 PM (e)

I’m curious —- are there any indications that prions, when they reproduce, are capable of changing and then reproducing those changes?

There certainly are different “strains” of prions, that is, alternatively folded prionic forms of the same protein (they also have different propagation properties - “fitness” if you will). I am not sure if one prion strain can spontaneously “mutate” into another, although that might perhaps be possible at some low rate, just like a normal protein can on occasion misfold spontaneously into a prion.

Comment #109416

Posted by jr on June 30, 2006 4:27 AM (e)

I want to do more study about prions

Comment #109426

Posted by 'Rev Dr' Lenny Flank on June 30, 2006 5:50 AM (e)

I am not sure if one prion strain can spontaneously “mutate” into another, although that might perhaps be possible at some low rate, just like a normal protein can on occasion misfold spontaneously into a prion.

I’m not sure either, and that’s what I’m asking.

If a prion can indeed spontaneously mis-fold into another form, and then that form gets copied, and then passed on to another host, where it can also mis-fold again, and pass on THAT copy, then it would seem reasonable that some foldings would be more efficient than others. I.e., there would be replication, mutation, selection, and reproduction of the selected mutations. NASA’s definition of “life”.

;)

Comment #109455

Posted by qetzal on June 30, 2006 9:02 AM (e)

'Rev Dr' Lenny Flank wrote:

If a prion can indeed spontaneously mis-fold into another form, and then that form gets copied, and then passed on to another host, where it can also mis-fold again, and pass on THAT copy, then it would seem reasonable that some foldings would be more efficient than others. I.e., there would be replication, mutation, selection, and reproduction of the selected mutations. NASA’s definition of “life”.

It’s interesting to consider whether prions can really be said to replicate. They certainly don’t do so in the conventional sense that DNA or a virus does. A mis-folded prion protein can only ‘replicate’ by inducing an existing, normally-folded protein molecule to become mis-folded. (Sort of like Vonnegut’s Ice-9.)

Without a source of the normally-folded protein, the prion can’t propagate. On the other hand, essentially every current living replicator requires a pre-existing source of biological molecules, so maybe there’s no real distinction.

Comment #109469

Posted by William E Emba on June 30, 2006 11:16 AM (e)

'Rev Dr' Lenny Flank wrote:

If a prion can indeed spontaneously mis-fold into another form, and then that form gets copied, and then passed on to another host, where it can also mis-fold again, and pass on THAT copy, then it would seem reasonable that some foldings would be more efficient than others. I.e., there would be replication, mutation, selection, and reproduction of the selected mutations. NASA’s definition of “life”.

Crystals also replicate off a template. This is the basis of Cairns-Smith Genetic Takeover: crystals too would misform, and some errors by chance would be superior at replicating.

Comment #109474

Posted by Jim Harrison on June 30, 2006 11:56 AM (e)

Theoretical biologists and philosophers of science have defined what’s necessary for evolution by natural selection in abstract terms. Roughly speaking, any imperfect replicator whose copies are more or less likely to replicate themselves will evolve.

Comment #109529

Posted by 'Rev Dr' Lenny Flank on June 30, 2006 6:21 PM (e)

Crystals also replicate off a template. This is the basis of Cairns-Smith Genetic Takeover: crystals too would misform, and some errors by chance would be superior at replicating.

Yes, I’ve always thought that Cairns-Smith’s clay hypothesis was interesting.

The real problem seems to be NOT that we don’t have ANY good hypotheses about how life began, but we have TOO many, and not enough evidence yet to know which is on the right track.

Comment #109770

Posted by Albion on July 2, 2006 10:29 AM (e)

If creationists were going after germ theory the way they’re going after evolutionary theory, prions would be a very good example of something that “challenges the orthodoxy” or “deals a fatal blow to a seriously weakened theory” or whatever else it is that creationists are so fond of claiming.

Which just goes to show that creationists aren’t bothered about challenges to specific aspects of theories unless the theories happen to be in current conflict with their theology.