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Author Topic:   Excellent paper-peptide self assembly
Loudmouth
Inactive Member


Message 16 of 50 (64167)
11-03-2003 12:46 PM


I think what is missing here is the size of the pre-biotic "test tube" or reaction chamber, as such. We are talking about the rise of life, perhaps only once, on the Earth, a pretty big place, in the span of millions of years. Looking at things from a molecular perspective, large numbers appear quite quickly. Avagadro's number for example is in the 10^22 range. Second, no one knows the precise sequence or length of the first peptide/protein or the first RNA/DNA sequence. So before anyone can call something impossible, I think they should take these into account.

Replies to this message:
 Message 18 by DNAunion, posted 11-03-2003 11:49 PM Loudmouth has replied

  
Loudmouth
Inactive Member


Message 20 of 50 (64435)
11-04-2003 6:54 PM
Reply to: Message 18 by DNAunion
11-03-2003 11:49 PM


/*DNAunion*/ The paper I was addressing gave us this. But, the value it gave was overstated (as I already pointed out).
Sorry, I must have missed something. Did the paper limit the OoL to specific conditions or rule out others? What I am trying to get at is that Earth is a pretty big place, we're not talking about someone's backyard pool here.
*DNAunion*/ The two key things are (1) how improbable an event is, and (2) how many shots are available to hit the target. "Large numbers" of attempts don't do too much for us if the inverse of the probability is an even larger number.
Also, the number of shots are frequently based on unreasonable assumptions, such as the ignoring of side reactions, starting with "The Molecular Biologist's Dream: 'Once upon a time there was a prebiotic pool full of [beta]-D-nucleotides...'"*, and so on.
Unless you can quantitate the chances over say a 50 million year timespan you can't claim that the odds are against it. So, how does the inverse of the probability outweigh the chances? How many chances were there? Why do you feel they are unreasonable?
*DNAunion*/ But they do have fairly good ideas how long an RNA molecule would have to be in order to self-replicate. Orgel and Joyce estimated that it would have to be at least 40 monomers in length in order to be able to fold up into a complex enough shape to perform the required function. Experiments since have found that such is probably far too low: the closed thing yet to a self-replicator that has been designed was about 180 nucleotides long.
RNA as the catalyst for life is still a theory, although it has good backing it seems. The question is could a RNA 20mer plus a peptide 20mer be involved? How specific does the sequence have to be? The fact that pseudo self-replicating RNA has been observed at 180mers does not rule out anything.

This message is a reply to:
 Message 18 by DNAunion, posted 11-03-2003 11:49 PM DNAunion has replied

Replies to this message:
 Message 21 by DNAunion, posted 11-05-2003 9:16 PM Loudmouth has replied

  
Loudmouth
Inactive Member


Message 22 of 50 (65020)
11-07-2003 6:41 PM
Reply to: Message 21 by DNAunion
11-05-2003 9:16 PM


So not getting too technical, in order for two RNA replicases to exist simultaneously (one to copy the other to get things started) Joyce and Orgel calculate that there would need to be a library of about 10^48 unique RNAs, all existing at the same time. But Loewenstein calculates that there were only 10^48 total chemical trials over a 900 million year time span.
Of course there is more to be said, but that’s a lot to digest so perhaps I should refrain from going farther at this point.
I don't see why the whole library has to be existant at the same time, maybe you could fill me in. I understood it to be a 1 in 10^48 chance so that all is needed is 10^48 tries for a decent chance of the correct ribozyme to come about by chance.
This is an interesting debate, plan to read up and get back to it. Ribozymes and hypercycles aren't especially my specialty, but it does interest me. Any suggestions for online sources?

This message is a reply to:
 Message 21 by DNAunion, posted 11-05-2003 9:16 PM DNAunion has replied

Replies to this message:
 Message 24 by DNAunion, posted 11-08-2003 1:55 AM Loudmouth has not replied
 Message 25 by DNAunion, posted 11-08-2003 12:29 PM Loudmouth has not replied

  
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