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Author Topic:   The Recurrent Problem of Chirality
melatonin
Member (Idle past 6323 days)
Posts: 126
From: Cymru
Joined: 02-13-2006


Message 16 of 81 (320937)
06-12-2006 8:03 PM
Reply to: Message 1 by Evopeach
02-09-2006 4:49 PM


I know this is an old post but thought I'd stick this here.
A recent paper showed how cosmic radiation could cause a bias towards L-amino acids in space (I could find the ref if required). Last week another study (Klusserman et al. 2006, Nature 441) indicated that whether the original compostion of amino acids be 100:1 levo/dextro or 100:99 levo/dextro - the resulting solution will be predominately levo. So would not a cosmic source of amino acids with a slight bias towards levo become overwhelmingly levo when deposited on dissolved on the earth?

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Coragyps
Member (Idle past 849 days)
Posts: 5553
From: Snyder, Texas, USA
Joined: 11-12-2002


Message 17 of 81 (320945)
06-12-2006 8:41 PM
Reply to: Message 16 by melatonin
06-12-2006 8:03 PM


Wow! Give us more - I've let my Nature subscription lapse.

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melatonin
Member (Idle past 6323 days)
Posts: 126
From: Cymru
Joined: 02-13-2006


Message 18 of 81 (320950)
06-12-2006 8:53 PM
Reply to: Message 17 by Coragyps
06-12-2006 8:41 PM


Right-handed amino acids were left behind
02 June 2006
NewScientist.com news service
A CLUE to the mystery of how nature selected left-handed amino acids rather right-handed ones may lie in the way the substances behave as they dissolve in water.
Amino acids can appear in left-handed (L) and right-handed (D) mirror-image forms. When made from scratch in the lab the two versions are equally likely to appear, but in nature, L amino acids dominate.
Donna Blackmond at Imperial College London and colleagues dissolved a mixture of solid L and D versions of the amino acid serine in water. They found that a small difference in the initial proportion of one version gets amplified in the resulting solution. So a 100:1 mixture of L- and D-serine produces a solution made up almost entirely of L-serine, but so does a 100:99 mixture (Nature, vol 441, p 621).
"It doesn't matter what proportions of solid amino acids you throw in, you always get exactly the same proportions in solution," says Blackmond, whose team has found a similar effect with other amino acids. She says she is surprised that no one noticed the effect before.
This effect could have amplified a slight excess of L-amino acids in nature. Why there was a slight excess to start with is another question.
http://www.newscientist.com/channel/life/mg19025545.200.html
Here's a YSI link of the Klasserman et al. 2006 article (pdf format)...
Hightail

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Bradcap1
Inactive Member


Message 19 of 81 (334022)
07-21-2006 2:26 PM
Reply to: Message 1 by Evopeach
02-09-2006 4:49 PM


>Life cannnot begin or proceed using racemic mixtures of the two >forms for life molecules.
Life could have began using D-amino acids. It did not. The fact that all living organisms use L-amino acids is very strong evidence of common descent.
>More importantly perhaps is the fact that it is only the three >dimensional aspect of the molecules and their coiled shape in the >double helix of the DNA that enables them to store the information >contained in the "genetic code" sequences non-linearly rather than >linearly in two dimensions.
I don't think you understand the concept of "handedness" in biological molecules. Nor do you understand the structure of DNA. DNA is not made of amino acids in either form. DNA consists of nucleotides.

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RAZD
Member (Idle past 1519 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 20 of 81 (334135)
07-21-2006 9:45 PM
Reply to: Message 19 by Bradcap1
07-21-2006 2:26 PM


welcome to the fray
type [qs]quote boxes are easy[/qs] and it becomes:
quote boxes are easy
Life could have began using D-amino acids. It did not.
It also could have started with both, just found that it works better with one - at this point we don't know.
Enjoy.

Join the effort to unravel {AIDSHIV} with Team EvC! (click)

we are limited in our ability to understand
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RebelAAmericanOZen[Deist
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 Message 21 by Dr Adequate, posted 07-22-2006 12:32 AM RAZD has replied

  
Dr Adequate
Member (Idle past 399 days)
Posts: 16113
Joined: 07-20-2006


Message 21 of 81 (334186)
07-22-2006 12:32 AM
Reply to: Message 20 by RAZD
07-21-2006 9:45 PM


Chirality is autocatalytic.
A peptide replicator can amplify the proportion of a single chirality in an initially random mixture of left- and right-handed fragments:
Saghatelian, A., Y. Yokobayashi, K. Soltani and M. R. Ghadiri. 2001. A chiroselective peptide replicator; Nature 409: 797-801.
A demonstration of autocatalysis of chirality in amino acids:
Suju P. Mathew, Hiroshi Iwamura* and Donna G. Blackmond : Amplification of Enantiomeric Excess in a Proline-Mediated Reaction, Angewandte Chemie International Edition Vol 43, Issue 25 (June 21, 2004)
Self-assemblies on two-dimensional surfaces amplify a single handedness:
Zepik, H. et al. 2002. Chiral amplification of oligopeptides in two-dimensional crystalline self-assemblies on water; Science 295: 1266-1269
Serine forms stable clusters of a single handedness which can select other amino acids of like handedness; these clusters also incorporate other biologically important molecules such as glyceraldehyde, glucose, and phosphoric acid.
Takats, Zoltan, Sergio C. Nanita and R. Graham Cooks. 2003. Serine octamer reactions: indicators of prebiotic relevance; Angewandte Chemie International Edition 42: 3521-3523.
More of the same. You get the picture :
Sandra Pizzarello and Arthur L. Weber Prebiotic Amino Acids as Asymmetric Catalysts, Science 20 February 2004: Vol. 303. no. 5661, p. 1151
And yet another mechanism:
Martin Klussmann, Hiroshi Iwamura, Suju P. Mathew, David H. Wells, Jr Urvish Pandya, Alan Armstrong and Donna G. Blackmond; Thermodynamic control of asymmetric amplification in amino acid catalysis; Nature 441, 621-623 (1 June 2006)
The homeochirality of living species:
Pedro Cintas, Chirality of Living Systems: A Helping Hand from Crystals and Oligopeptides Angewandte Chemie International Edition, Volume 41, Issue 7 , Pages 1139 - 1145
Left handed amino acids catalyze production of dextrose sugars:
Pizzarello, Sandra, Arthur L. Weber. 2004 Prebiotic Amino Acids as Asymmetric Catalysts Science Vol 303, Issue 5661, 1151, 20 February 2004
The presence of borate minerals produces sugars in right-handed form:
Ricardo, A., Carrigan, M. A., Olcott, A. N., Benner, S. A.. 2004 Borate Minerals Stabilize Ribose Science January 9; 303: 196
Dextrose sugars fall out of the sky:
Sephton, Mark A. 2001 Meteoritics: Life’s sweet beginnings? Nature 414, 857 - 858 (20 Dec)
A mechanism by which a small initial imbalance in chirality can become overwhelming :
Kenso Soai, Takanori Shibata, Hiroshi Morioka & Kaori Choji. Asymmetric autocatalysis and amplification of enantiomeric excess of a chiral molecule, Nature 378, 767 - 768 (28 December 1995);
Shows a large and symmetric population of D and L crystals moving into complete chiral purity, with one of the enantiomers completely disappearing.
Cristobal Viedma, Chiral Symmetry Breaking During Crystallization: Complete Chiral Purity Induced by Nonlinear Autocatalysis and Recycling, Phys. Rev. Lett. 94, 065504 (2005)
Edited by Dr Adequate, : Trying to fix one of the links.

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Dr Adequate
Member (Idle past 399 days)
Posts: 16113
Joined: 07-20-2006


Message 22 of 81 (334187)
07-22-2006 12:38 AM


...
Edited by Dr Adequate, : Double post

  
RAZD
Member (Idle past 1519 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 23 of 81 (334239)
07-22-2006 9:28 AM
Reply to: Message 21 by Dr Adequate
07-22-2006 12:32 AM


Chirality is autocatalytic.
A peptide replicator can amplify the proportion of a single chirality in an initially random mixture of left- and right-handed fragments: ...
This is why I think it is possible for early {proto-life\animate} systems to have started with a general mix and then selected for one chirality. It didn't have to start with only one.
Consider early proto-life using both, and needing mechanisms to use both, then selection for simpler systems that only use one, eventually requiring that all are one-handed for the simplest system.
There also seems to be a slight bias to L- vs D- if I recall, that may have been crucial to it being selected.
Nice links. You have one I used in in my essay RAZD - Building Blocks of Life (sweet meteorites)
Enjoy.

Join the effort to unravel {AIDSHIV} with Team EvC! (click)

we are limited in our ability to understand
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Brad McFall
Member (Idle past 5147 days)
Posts: 3428
From: Ithaca,NY, USA
Joined: 12-20-2001


Message 24 of 81 (334300)
07-22-2006 3:45 PM
Reply to: Message 19 by Bradcap1
07-21-2006 2:26 PM


If you were speaking
of the two >forms
for any molecules in living things and found
quote:
(m)ore importantly perhaps is the fact that it is only the three >dimensional aspect of the molecules and their coiled shape in the >double helix of the DNA that enables them to store the information >contained in the "genetic code" sequences non-linearly rather than >linearly
then it seems it *may* matter if one was D or L, logically.
If you alternatively had orginally decided that all molecular formations could be deducted back to TWO FORMS during life then what you said "more" importanly would be MORE important besides.
Did you say this? It does not seem you did.
There could simply be linearity and a point at infinity, but one would have to cash in continuously Gould's insistance (in "The Structure of Evolutionary Theory") for instance that, with every competative victor there is also a detriment (in his "calculus" of species' life and death).

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Bradcap1
Inactive Member


Message 25 of 81 (334307)
07-22-2006 4:51 PM
Reply to: Message 24 by Brad McFall
07-22-2006 3:45 PM


If you alternatively had orginally decided that all molecular formations could be deducted back to TWO FORMS during life then what you said "more" importanly would be MORE important besides.
I was responding to the Evopeach. He's been running from me for a while. I didn't know the mechanics of identifying others quotes. Radz got me straight.

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Replies to this message:
 Message 26 by Brad McFall, posted 07-23-2006 4:14 PM Bradcap1 has replied
 Message 28 by RAZD, posted 07-23-2006 5:03 PM Bradcap1 has replied

  
Brad McFall
Member (Idle past 5147 days)
Posts: 3428
From: Ithaca,NY, USA
Joined: 12-20-2001


Message 26 of 81 (334549)
07-23-2006 4:14 PM
Reply to: Message 25 by Bradcap1
07-22-2006 4:51 PM


scaling 1-D symmetries
You started to to say:
quote:
>Life cannnot begin or proceed using racemic mixtures of the two >forms for life molecules.
evopeach by bradcap1
quote:
Life could have began using D-amino acids. It did not. The fact that all living organisms use L-amino acids is very strong evidence of common descent.
bradcap1
previously and then after quoting EvoPeach one more time you said,
quote:
I don't think you understand the concept of "handedness" in biological molecules.
I dont think it was nor is going to matter what Razd had to say relative to the point I was trying to make. If you are only trying to "pull" Evopeach's tongue then you could ignore my comment but I think it holds nonetheless.
Evopeach seemed to me to try to take Kant's argument for the existence of GOD by the manifestation of the difference of RIGHT and LEFT and to extend this to the discussion of chirality.
I was reacting to your thought that either sides' factuality (you fell to the D-side)is evidential for Common Descent.
I do not believe this to be the case.
Edited by Brad McFall, : BBCODE

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RAZD
Member (Idle past 1519 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 27 of 81 (334553)
07-23-2006 4:59 PM
Reply to: Message 26 by Brad McFall
07-23-2006 4:14 PM


Re: scaling 1-D symmetries
hey Brad (McFall v cap1).
... matter what Razd had to say relative to ...
bradcap1 was refering to his manner of quoting evopeach, rather than any specific content of my message I believe, and that I showed him how to use quoteboxes.
Evopeach seemed to me to try to take Kant's argument for the existence of GOD by the manifestation of the difference of RIGHT and LEFT and to extend this to the discussion of chirality.
I agree that this is the common argument, that amino acids come in ambidextrous ambiguity, and that {selection} for {one v other v both} handedness shows a {hand} in the matter of an external source or function.
It amuses me that the choice is so sinister in appearance (when it could just be accidental, a flip of the cosmic coin).
I was reacting to your thought that either sides' factuality (you fell to the D-side)is evidential for Common Descent.
I do not believe this to be the case.
And it may not have been "common" descent but a mixed metaphor descent in the early (flat) stages before the hills. Unfortunately belief has no effect on (a) evidence or (2) the past, so we may never know.
It also has not been shown that a opposite hand life cannot form, nor one with mixed ratios (the question becoming then, is one more fit than others? ... if one keeps to evo-principles, or is one blessed versus sinned? ... if one keeps to {largess handed oblige} principles ...)
Enjoy.

Join the effort to unravel {AIDSHIV} with Team EvC! (click)

we are limited in our ability to understand
by our ability to understand
RebelAAmericanOZen[Deist
... to learn ... to think ... to live ... to laugh ...
to share.

This message is a reply to:
 Message 26 by Brad McFall, posted 07-23-2006 4:14 PM Brad McFall has replied

Replies to this message:
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RAZD
Member (Idle past 1519 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 28 of 81 (334555)
07-23-2006 5:03 PM
Reply to: Message 25 by Bradcap1
07-22-2006 4:51 PM


I'm curious ...
I was responding to the Evopeach. He's been running from me for a while.
You've only posted 2 times on this whole forum, once to Evopeach and once to Brad McFall.
Just curious.
and Evopeach has not posted since february ...
Edited by RAZD, : added last line

Join the effort to unravel {AIDSHIV} with Team EvC! (click)

we are limited in our ability to understand
by our ability to understand
RebelAAmericanOZen[Deist
... to learn ... to think ... to live ... to laugh ...
to share.

This message is a reply to:
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Iname
Junior Member (Idle past 3999 days)
Posts: 28
Joined: 06-08-2006


Message 29 of 81 (334566)
07-23-2006 5:48 PM
Reply to: Message 28 by RAZD
07-23-2006 5:03 PM


Re: I'm curious ...
He may have been talking with Evopeach on another forum. He's posted at Panda's Thumb before and probably trolls several other forums.

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RAZD
Member (Idle past 1519 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 30 of 81 (334578)
07-23-2006 6:12 PM
Reply to: Message 29 by Iname
07-23-2006 5:48 PM


Re: I'm curious ...
so he's a stalker?
LOL.
welcome to the fray ... lurker?

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