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Author Topic:   Self Replicating molecules
Tranquility Base
Inactive Member


Message 3 of 25 (14424)
07-29-2002 9:29 PM
Reply to: Message 1 by singularity
07-29-2002 6:50 AM


Yes this is fascinating stuff. As an ex-peptide person (I used to work on peptide toxins) I am aware of this but it is also extremely clear that this could (i) not systematically replicate an arbitary sequence (it only works for coiled-coils) and (ii) is not related to the way in which DNA replicates. Perhaps this will become known as the coiled-coil world (ala the RNA world)?
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Tranquility Base
Inactive Member


Message 5 of 25 (14433)
07-29-2002 9:49 PM
Reply to: Message 4 by John
07-29-2002 9:35 PM


The point is that arbitrary DNA seqeunces replicate (via a host of enzyme systems). Peptides will not - only a few special sequences will. It's fascinating (I've been kicking myself ever since for not thinking of it) but it's not a systematic replication system.

[This message has been edited by Tranquility Base, 07-29-2002]


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 Message 4 by John, posted 07-29-2002 9:35 PM John has responded

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 Message 6 by John, posted 07-29-2002 9:53 PM Tranquility Base has responded
 Message 9 by axial soliton, posted 07-30-2002 2:22 AM Tranquility Base has responded
 Message 15 by Brad McFall, posted 08-05-2002 11:55 AM Tranquility Base has not yet responded

  
Tranquility Base
Inactive Member


Message 7 of 25 (14441)
07-29-2002 10:37 PM
Reply to: Message 6 by John
07-29-2002 9:53 PM


No-one has outlined how one can go from a self replicating peptide to a cell! I thought this was a CvsE BBS?
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Tranquility Base
Inactive Member


Message 11 of 25 (14601)
07-31-2002 10:20 PM
Reply to: Message 9 by axial soliton
07-30-2002 2:22 AM


In the case of the coiled coil peptides I fully understand how the self replication works - it is not a mystery and it is very clear that it will only work for special seqeunces that fold into coiled coils.

The coiled coils we are talking about are (eg) homodimeric (ie a two molecule coil with each molecule the same) that associates (binds) due to self-affinity in a symetric manner presumably.

The key point is that becasue the molecule binds to itslef strongly it will probably also bind to the component amino-acids weakly. So that means that a single molecule of the peptide will bind to amino-acids floating around. These amino-acids will be briefly held near to each other in the correct sequence and cause a weak catalytic enhancement of spontaneous peptide bond formaiton joining two amino-acids together. This 'dipeptide' (two amin-acids) will now probably bind to the full peptide more strongly and make it more easy to get the next amino-acids to bind in seqeunce and catalytically bond. Eventaully the whole peptide will have replicated itself by this means. This is my understanding of how it works, it makes snese and it is presuamably the thinking that suggested the experiment. But it wil onyl work for coiled coil sequences that have enough self binding affinity and sequence specific selectivity. DNA replication does not require the DNA seqeucne to form any particular structure (like a coiled coil) - the double spirial helix is not important for replicaiton per se - it is the fact that A likes to bind to T and G to C. And all DNA coils anyway. Only very few peptides from cioiled coils. The peptide issue only works becasue the peptide sequence is somehow complementary to itself due to 3D structure and sequence.

Please correct me anyone if that is not how it works.

[This message has been edited by Tranquility Base, 07-31-2002]


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