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Author Topic:   What is Life?
Stephen Push
Member (Idle past 3056 days)
Posts: 140
From: Virginia, USA
Joined: 10-08-2010


Message 86 of 268 (593052)
11-23-2010 10:26 PM
Reply to: Message 71 by Dr Adequate
11-23-2010 12:12 PM


Re: Life?
Dr Adequate writes:

Life is a collection of chemicals that, given the right environmental conditions, can promote their own synthesis through surface catalysis.

Are prions life according to that definition?


This message is a reply to:
 Message 71 by Dr Adequate, posted 11-23-2010 12:12 PM Dr Adequate has responded

Replies to this message:
 Message 87 by Dr Adequate, posted 11-23-2010 10:42 PM Stephen Push has responded

  
Stephen Push
Member (Idle past 3056 days)
Posts: 140
From: Virginia, USA
Joined: 10-08-2010


Message 88 of 268 (593085)
11-24-2010 7:31 AM
Reply to: Message 87 by Dr Adequate
11-23-2010 10:42 PM


Re: Life?
Dr Adequate writes:

No. The infectious prions make normal prions change their shape to that of infectious prions. But they do not catalyze the synthesis of infectious prions.

The prevailing theory of prion replication involves "autocatalytic protein misfolding." Why wouldn't that fall within your definition of "life"?

Recent research also shows that, although they lack nucleic acids, prions undergo Darwinian evolution, including mutation and natural selection. That finding is irrelevant to your definition, but it would appear to bolster the case for considering prions to be a form of life -- at least in the same sense that viruses could be consider a form of life.

Edited by Stephen Push, : No reason given.


This message is a reply to:
 Message 87 by Dr Adequate, posted 11-23-2010 10:42 PM Dr Adequate has responded

Replies to this message:
 Message 93 by Dr Adequate, posted 11-24-2010 11:01 AM Stephen Push has responded

  
Stephen Push
Member (Idle past 3056 days)
Posts: 140
From: Virginia, USA
Joined: 10-08-2010


Message 95 of 268 (593197)
11-24-2010 9:51 PM
Reply to: Message 93 by Dr Adequate
11-24-2010 11:01 AM


Re: Life?
Dr Adequate writes:

Interesting, I'd like to look at that research, if you have a link. Thanks.

Darwinian Evolution of Prions in Cell Culture. Science, 12 February 2010: 869-872.

That page also contains links to two critical responses to the research paper and a rebuttal from one of the paper's authors.

But my feeling is that they aren't really performing reproduction as such.

Although the requirement of synthesis in your definition excludes prions, why isn't the method by which prions replicate themselves a form of reproduction?

Question: is it possible to come up with a simple definition which includes prions but excludes the growth of crystals in solution?

Life is any chemical entity that replicates itself and evolves by means of mutation and natural selection.

OR

Life is any entity composed of organic molecules that replicates itself.

Assuming the prion evolution theory holds up, I would prefer the first definition, since it would have the advantage of admitting extraterrestrial life that may not be based on organic chemistry.

Edited by Stephen Push, : No reason given.


This message is a reply to:
 Message 93 by Dr Adequate, posted 11-24-2010 11:01 AM Dr Adequate has not yet responded

  
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