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Author Topic:   What is Life?
Dr Adequate
Member (Idle past 284 days)
Posts: 16113
Joined: 07-20-2006


Message 76 of 268 (592987)
11-23-2010 12:39 PM
Reply to: Message 73 by Straggler
11-23-2010 12:20 PM


Re: Life?
Is a virus a form of life by this definition?
Yes.

This message is a reply to:
 Message 73 by Straggler, posted 11-23-2010 12:20 PM Straggler has replied

Replies to this message:
 Message 77 by Straggler, posted 11-23-2010 12:43 PM Dr Adequate has replied

  
Straggler
Member
Posts: 10333
From: London England
Joined: 09-30-2006


Message 77 of 268 (592988)
11-23-2010 12:43 PM
Reply to: Message 76 by Dr Adequate
11-23-2010 12:39 PM


Re: Life?
Is a strand of RNA a form of life by this definition?

This message is a reply to:
 Message 76 by Dr Adequate, posted 11-23-2010 12:39 PM Dr Adequate has replied

Replies to this message:
 Message 79 by Dr Adequate, posted 11-23-2010 1:02 PM Straggler has replied

  
crashfrog
Member (Idle past 1466 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 78 of 268 (592996)
11-23-2010 12:54 PM
Reply to: Message 71 by Dr Adequate
11-23-2010 12:12 PM


Re: Life?
Life is a collection of chemicals that, given the right environmental conditions, can promote their own synthesis through surface catalysis.
Interesting and potentially broad. To me it makes sense to distinguish between collections of chemicals that both promote their own synthesis and do redox chemistry, which I would call "life"; and collections of chemicals that simply replicate, which you define as "life" but I would probably call "proto-life" or "life-like" or something.
I think you have to have a metabolism to be alive. Mere self-replication, in my opinion, doesn't allow for the expansive diversity and complexity that characterizes living things. The crucial step, to me, is metabolism.
Of course, by my definition battery-powered machines could be alive. The minute Roombas start assembling other Roombas, I guess they're alive.

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

Replies to this message:
 Message 81 by Dr Adequate, posted 11-23-2010 1:16 PM crashfrog has replied

  
Dr Adequate
Member (Idle past 284 days)
Posts: 16113
Joined: 07-20-2006


Message 79 of 268 (592997)
11-23-2010 1:02 PM
Reply to: Message 77 by Straggler
11-23-2010 12:43 PM


Re: Life?
Is a strand of RNA a form of life by this definition?
I guess it would include RNA species, sure. But not prions, before you ask.
I think I see where you're going, and I foresee difficulties with my proposed definition. I may have ponder this more carefully.

This message is a reply to:
 Message 77 by Straggler, posted 11-23-2010 12:43 PM Straggler has replied

Replies to this message:
 Message 80 by Straggler, posted 11-23-2010 1:07 PM Dr Adequate has replied

  
Straggler
Member
Posts: 10333
From: London England
Joined: 09-30-2006


Message 80 of 268 (592998)
11-23-2010 1:07 PM
Reply to: Message 79 by Dr Adequate
11-23-2010 1:02 PM


Re: Life?
To be honest I was primarily asking because I don't know the answer to my own questions.
I wanted to know where the boundary imposed by your definition lay in terms I could understand.
But if it made you think more about the definition in question then I guess that is a good thing.

This message is a reply to:
 Message 79 by Dr Adequate, posted 11-23-2010 1:02 PM Dr Adequate has replied

Replies to this message:
 Message 82 by Dr Adequate, posted 11-23-2010 1:29 PM Straggler has not replied

  
Dr Adequate
Member (Idle past 284 days)
Posts: 16113
Joined: 07-20-2006


Message 81 of 268 (593000)
11-23-2010 1:16 PM
Reply to: Message 78 by crashfrog
11-23-2010 12:54 PM


Re: Life?
Interesting and potentially broad. To me it makes sense to distinguish between collections of chemicals that both promote their own synthesis and do redox chemistry ...
That sounds like a good way to capture certain concepts of life. I like it.
I wonder, though, whether it might exclude certain kinds of "life, but not as we know it". I am not even remotely good at chemistry, but it seems that acid-base reactions (for example) are not redox reactions. Now, can we imagine something which we would like to call "life" having what we would like to call a "metabolism" which use that sort of chemistry instead? Or is there some chemical reason why this is inconceivable?
I think you have to have a metabolism to be alive. Mere self-replication, in my opinion, doesn't allow for the expansive diversity and complexity that characterizes living things. The crucial step, to me, is metabolism.
Well, this is exactly why there's a gray area. My gut tells me that viruses should be categorized as life, and in the end our guts are all we have to go on --- there's no objectively correct definition.
Of course, by my definition battery-powered machines could be alive. The minute Roombas start assembling other Roombas, I guess they're alive.
What if this doesn't involve redox chemistry?

This message is a reply to:
 Message 78 by crashfrog, posted 11-23-2010 12:54 PM crashfrog has replied

Replies to this message:
 Message 83 by crashfrog, posted 11-23-2010 2:48 PM Dr Adequate has replied

  
Dr Adequate
Member (Idle past 284 days)
Posts: 16113
Joined: 07-20-2006


Message 82 of 268 (593001)
11-23-2010 1:29 PM
Reply to: Message 80 by Straggler
11-23-2010 1:07 PM


Re: Life?
But if it made you think more about the definition in question then I guess that is a good thing.
Well I think the problem might be that I haven't shown how to draw a line between the chemicals in question and the "right environment" that I mentioned, and this might become problematic if we pushed it far enough.
I could wish my knowledge of chemistry was more extensive.

This message is a reply to:
 Message 80 by Straggler, posted 11-23-2010 1:07 PM Straggler has not replied

  
crashfrog
Member (Idle past 1466 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 83 of 268 (593012)
11-23-2010 2:48 PM
Reply to: Message 81 by Dr Adequate
11-23-2010 1:16 PM


Re: Life?
Now, can we imagine something which we would like to call "life" having what we would like to call a "metabolism" which use that sort of chemistry instead? Or is there some chemical reason why this is inconceivable?
I don't know if you can "make a living" on acid-base chemistry, because I don't think there's a high enough change in free energy to exploit.
For the most part - and I obviously have no way to be sure this is true, just as you have no way to be sure it's not - I think that the biochemistry of life on Earth, particularly of microbes, is so broad and diverse that it essentially encompasses the width and breadth of all the ways it's possible to "make a living" as a chemistry-based organism in this universe. If it's possible to make a living off of acid-base chemistry we should be able to find an organism on Earth that is.
Could our mitochondria be an example? ATP synthesis in mitochondria is driven by the energy stored as a substantial pH difference between the matrix and the intermembraneous space. The pH gradient is established by a series of proton pumps that are driven by energy from the TCA cycle (if I'm remembering this right.) So there's a way we're all making a living off of pH changes. But, say, the neutralization of acid by base? It's possible, but maybe we don't see it because the little guys get their lunch eaten by the redox guys who outcompete them.
Or is there some chemical reason why this is inconceivable?
I wouldn't say "inconceivable", but perhaps unlikely. Of course, the one thing that's always true in biology is that you can't say that anything is always true in biology.
My gut tells me that viruses should be categorized as life
As full-on life? My gut tells me they're life-like.
I don't expect you to ignore your gut for mine, of course, and I'm happy to accept all forms of disagreement on this issue. I'm certain that my definition will eventually be revealed to exclude something I "know" is life and include something I "know" is not. Yours, too. It's the problem with definitions.
What if this doesn't involve redox chemistry?
Well, I mentioned batteries because batteries operate by redox. (All forms of battery. If it's not redox, it's not a battery. Capacitors, for instance, are not batteries.) But, say, nuclear-powered self-replicating robots? I'm prepared to accept that as life even though we're now talking about "organisms" that engage in no chemistry whatsoever. But I think I'd create a different definition for such creatures.

This message is a reply to:
 Message 81 by Dr Adequate, posted 11-23-2010 1:16 PM Dr Adequate has replied

Replies to this message:
 Message 84 by Dr Adequate, posted 11-23-2010 3:00 PM crashfrog has replied

  
Dr Adequate
Member (Idle past 284 days)
Posts: 16113
Joined: 07-20-2006


Message 84 of 268 (593013)
11-23-2010 3:00 PM
Reply to: Message 83 by crashfrog
11-23-2010 2:48 PM


Re: Life?
I don't know if you can "make a living" on acid-base chemistry, because I don't think there's a high enough change in free energy to exploit.
But if they did, you'd want to call them "life", wouldn't you?
Well, I mentioned batteries because batteries operate by redox.
You see the things I don't know?
I do know that if they were battery-powered, the laws of thermodynamics would eventually stop your replication process. You'd want them solar-powered or something.

This message is a reply to:
 Message 83 by crashfrog, posted 11-23-2010 2:48 PM crashfrog has replied

Replies to this message:
 Message 85 by crashfrog, posted 11-23-2010 3:58 PM Dr Adequate has not replied

  
crashfrog
Member (Idle past 1466 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 85 of 268 (593016)
11-23-2010 3:58 PM
Reply to: Message 84 by Dr Adequate
11-23-2010 3:00 PM


Re: Life?
But if they did, you'd want to call them "life", wouldn't you?
Can I say "it would depend"?
Maybe the definitions game is for mugs, I dunno. Maybe it's just better to go case by case.
You'd want them solar-powered or something.
Sure, ultimately some of them have to be solar-powered, yes.

This message is a reply to:
 Message 84 by Dr Adequate, posted 11-23-2010 3:00 PM Dr Adequate has not replied

  
Stephen Push
Member (Idle past 4859 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 replied

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

  
Dr Adequate
Member (Idle past 284 days)
Posts: 16113
Joined: 07-20-2006


Message 87 of 268 (593056)
11-23-2010 10:42 PM
Reply to: Message 86 by Stephen Push
11-23-2010 10:26 PM


Re: Life?
Are prions life according to that definition?
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.

This message is a reply to:
 Message 86 by Stephen Push, posted 11-23-2010 10:26 PM Stephen Push has replied

Replies to this message:
 Message 88 by Stephen Push, posted 11-24-2010 7:31 AM Dr Adequate has replied

  
Stephen Push
Member (Idle past 4859 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 replied

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

  
Dr Jack
Member
Posts: 3514
From: Immigrant in the land of Deutsch
Joined: 07-14-2003
Member Rating: 8.7


Message 89 of 268 (593086)
11-24-2010 7:53 AM
Reply to: Message 72 by Dr Adequate
11-23-2010 12:19 PM


Re: Viruses Again
I'm in the Viruses are not life camp, myself (and that, as far as I can tell, puts me in the same camp as the majority of Biologists - although perhaps not Virologists themselves).
So, just to clarify.
* Biology is the study of life.
* Viruses are (per your favored definition) not life.
So, tell me. If someone spends his whole scientific career studying viruses ... does that mean that he is not a biologist?
No, because the study of viruses is necessarily linked to the study of the living host of viruses. You cannot understand a virus without also understanding certain aspects of their hosts.

This message is a reply to:
 Message 72 by Dr Adequate, posted 11-23-2010 12:19 PM Dr Adequate has replied

Replies to this message:
 Message 92 by Dr Adequate, posted 11-24-2010 10:57 AM Dr Jack has replied

  
Jon
Inactive Member


(1)
Message 90 of 268 (593095)
11-24-2010 10:09 AM


It is What we Make It
The importance of the differences between life and non-life is the same as the importance of the differences between a rock and a mountain. And where does a rock begin and a mountain end? Is it important to anyone but us?
Since we're the only ones using the definition, it's probably best we just make one up; afterall, there will certainly be none discovered within nature herself.
If we count it as life, then it is life. How could it be any other way?
Jon

Check out Apollo's Temple!
Ignorance is temporary; you should be able to overcome it. - nwr

Replies to this message:
 Message 91 by Dr Adequate, posted 11-24-2010 10:54 AM Jon has replied

  
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