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Author Topic:   Could RNA start life?
crashfrog
Member (Idle past 1467 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 7 of 105 (682637)
12-04-2012 9:27 AM
Reply to: Message 5 by nwr
12-04-2012 7:10 AM


Personally, I am not committed to either, but I think "metabolism first" the more likely of the two.
I'm not sure I follow. Could you expand on this?
How do you see metabolism happening without catalysis? How do you see catalysis happening without either enzymes or autocatalytic nucleic acids? How do you see there being enzymes before nucleic acids? If autocatalytic nucleic acids predate enzymes, isn't that "RNA first"?

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 Message 5 by nwr, posted 12-04-2012 7:10 AM nwr has replied

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 Message 9 by nwr, posted 12-04-2012 10:28 AM crashfrog has replied

  
crashfrog
Member (Idle past 1467 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 11 of 105 (682683)
12-04-2012 3:21 PM
Reply to: Message 9 by nwr
12-04-2012 10:28 AM


Metabolism is a matter of chemical reactions releasing potential energy of chemical structure, and making that available as kinetic energy (producing motions). Spontaneously occurring chemical reactions do some of that.
Well, yes, but how does a putative proto-organism exploit any of that without some degree of catalysis?
For my own part, I can't imagine how you could have non-catalytic chemical life. But my BS is in biochemistry, so I'm already sort of primed to define life in terms of its ability to create a volume where chemical reactions are controlled to the organism's benefit. It's certainly the case that chemistry predates RNA, but in the context of "starting life" (you know, up there in the thread title) it's just not yet clear to me what you think.
Metabolism is a matter of living things using enzymes to catalyze chemical reactions to exploit the change in free energy. Obviously there are many spontaneous reactions that involve a favorable free energy change, as well. But unless an organism exploits the reaction it's not a form of metabolism, and unless the organism is participating in the reaction some way, the energy can't be exploited. So I still don't understand your position. But it's interesting, I'm not trying to draw you into an argument, I'm trying to draw you into being more clear. I'd love for you to expand on your thoughts.

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crashfrog
Member (Idle past 1467 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 12 of 105 (682684)
12-04-2012 3:27 PM
Reply to: Message 8 by New Cat's Eye
12-04-2012 10:14 AM


Given the right conditions, molecules just spontaneously react on their own. Its all according to physical laws. Biology is just complex chemistry and chemistry is just complex physics. There's no inventing or thought process, shit just happens.
Sure. But, it's not an unreasonable question to ask if we subtract the notion of "purpose" and wonder - what is the selective advantage of evolving storage of enzymes as nucleic acids if enzymes haven't yet evolved? At the Bio 101 level, there's a chicken and egg problem here - organisms require proteins for catalysis, proteins can only evolve when represented by DNA (chemical changes to your proteins themselves aren't heritable), but DNA can't have evolved without proteins.
The answer is the world of auto-catalytic RNA, where organisms are using and storing RNA sequences that can mutate and be inherited and exchanged, but also can be used for chemical catalysis. It's pretty good, we've discovered that cells still use RNA as both an information storage molecule and a catalytic molecule, and I've never heard a convincing alternative for how life could evolve from simple chemistry to the Central Dogma.

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crashfrog
Member (Idle past 1467 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 14 of 105 (682687)
12-04-2012 4:01 PM
Reply to: Message 13 by nwr
12-04-2012 3:55 PM


Perhaps you missed the "I am not committed to either" part of Message 5.
I didn't miss it, but you were pretty clear that you're leaning towards a position that I'm telling you, doesn't make any sense to me. Even if you were leaning away from it we'd still be talking about it because I don't see how it can even be one of the choices.
If you are committed to life magically popping into existence, then we will have to agree to disagree.
I'm not committed to life "magically popping into existence", and now I wonder where you got that I was. Again, I'm simply trying to arrive at clarity about your views. How do you have metabolism without catalysis, and how do you have biological catalysis without either enzymes or ribozymes? You insist that I'm overthinking it somehow, but these all seem like stupidly obvious questions to me. I'm wondering maybe if you didn't underthink it.
That allows a possible path for life to evolve out of spontaneously occurring chemistry.
Life certainly evolved out of spontaneously occurring chemistry, but it wouldn't be life until the chemistry was controlled and not spontaneous. Right?
Maybe I'm just not making myself clear yet. Let's try some more questions. Start with the first living thing (in your view.) Now, trace back one step to its immediate predecessor which by definition is not life, so let's call it the "last proto-life." What kind of chemistry does the last proto-life do, and how does it do it?

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crashfrog
Member (Idle past 1467 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 17 of 105 (682695)
12-04-2012 6:00 PM
Reply to: Message 15 by RAZD
12-04-2012 4:48 PM


Re: abiogenesis - last stages?
Life certainly evolved out of spontaneously occurring chemistry, but it wouldn't be life until the chemistry was controlled and not spontaneous. Right?
Why?
Well, and again this could just be me, but the "why" is because that's what I think life is. I can mix potassium chlorate and gummi bears in a reaction vessel on my countertop, and that reaction is (incredibly) spontaneous, but it would be absurd to describe it as "alive", or even as a form of metabolism even though when I eat a gummi bear, a very similar reaction is occurring. Why? Because all that energy is being wasted, it's all heat and light and loss of entropy.
That, to me, is the difference between a reaction between potassium chlorate and hydrocarbons on the countertop and a reaction between potassium chlorate and hydrocarbons occurring in the cell of some putative clorate-based "gummi bear-vore" - the difference between chemistry that occurs spontaneously and chemistry that occurs spontaneously and is exploited. And I don't see how you get to the exploitation part, chemically-speaking, without mediating and controlling the reaction via catalysis. Otherwise you don't have life (or even proto-life) you just have chemistry.

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crashfrog
Member (Idle past 1467 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 21 of 105 (682761)
12-05-2012 10:23 AM
Reply to: Message 20 by Genomicus
12-05-2012 10:08 AM


Re: Life is chemicals, not purposes
Oo, oo, let me try one! "There are no naturally-occurring Diels-Alderases."

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crashfrog
Member (Idle past 1467 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 40 of 105 (683563)
12-11-2012 5:30 PM
Reply to: Message 39 by Saiyan
12-11-2012 5:03 PM


RNA isn't made out of protein.

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