Why only L-AAs

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Why only L-AAs

Post by 2810712 » Wed Jan 04, 2006 2:39 pm

Why r only L-AA present in the natural proteins?
Why not a mixed composition i.e. both Ls and Ds.
or just Ds???
I have tried making something with the molecular mekano, i feel that mixed one is quite unstable or envolving non-uniform stability... But why not just D???
or its just by chance that only Ls are selected and not only Ds???

What about other such biomolecules[carbohydrates,lipids etc...]???
help me out, please.



hrushikesh

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Post by Nite » Sun Jan 08, 2006 12:35 pm

my group did a small project regarding this topic. did some reading of it last time. Most of the reasons are traced back to the origin of life. Like the aa that first existed on earth (which come from the outer space) consist of more L than D. This come from the examination of meteorite from the outer space.

The other is that it's due to the magnetic field (or radiation or something like that) that formed during the formation of a star (which could be earth) is more supportive for the formation of L-aa.

And some others which are beyond my level of understanding..

The following are the links that we used for the project:

http://www.ast.cam.ac.uk/AAO/local/www/ ... ality.html

http://ourworld.compuserve.com/homepage ... estion.htm

http://www.rae.org/revev6.html

http://www.madsci.org/posts/archives/ma ... .Bc.r.html

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Post by GreenDog » Sun Jan 08, 2006 1:10 pm

I think the answer resembles the answer to the question; why in most countries people drive on the right side of the road? Why not both? Why not on the left?
Well, it couldn’t have been both because they'd bump into each other.
And yes, it could be the left side like in Britain, but the reasons for it are historical – it just happened this way…
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cytochromeP
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Non-Conservation of Parity

Post by cytochromeP » Tue Jan 10, 2006 3:38 am

Hi,

The reason is 'assymetry of fundamental particles due to the non-conservation of parity of the universe.' Non-conservation of parity means that different laws apply to a hypothetical mirror image of our universe.

(watever that means....but sounds really cool...)

Reference: Physical Chemistry by P.W. Atkins.
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Post by Ultrashogun » Thu Jan 12, 2006 11:27 am

I read the link about the murchison asteroid and it seems legit, why have I never heard of it before? Is there some controversy regarding it?

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Post by 2810712 » Fri Jan 13, 2006 3:00 pm

Thanks!!!
Great links, especially i didn't know about that L-AAs from that asteroid...
there too why only L-AAs were there on that asteroid seems to be the logical questions.
"By chance" is the most...most...different scientific reasoning but still true...
How do you all make your self agree such a "by chance'' reasoning?
What are proper intuitions behind it???

Parity???Mirror image ??? Does our universe gets ready seeing its mirror image and goes to a party??? :D
Really cool... is this hypothisis cheched ???


Yours biolover[ not by chance!!!]
Shrei

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Post by Nite » Wed Jan 18, 2006 4:29 pm

i just adding this for fun.. my group mates come up with our own theory regarding this last time.

During early earth, there exist two different forms of organisms: one is the D-aa organisms, the other is the L-aa organisms.. they have different metabolic and genetic pathway, etc.. then one day something happen to the earth that killed all the D-aa (probably a very huge meteorite that hit the earth or sudden extreme change in the earth environment). Eventually, only left L-aa organisms which continue to grow, reproduce and proliferate..

Again.. it's just for funsake:p.


n btw, i have heard of some microbes can actually utilise D-aa.. such that D-aa is added to the media for differential selection..

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Post by MrMistery » Thu Jan 19, 2006 8:18 pm

Hm... your theory has flaus: How come the meteorite wiped out ALL the D-organisms and left L-organisms. Does that mean that L-organisms were "better"? If it's like that, then how?
"As a biologist, I firmly believe that when you're dead, you're dead. Except for what you live behind in history. That's the only afterlife" - J. Craig Venter

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Post by Nite » Fri Jan 20, 2006 1:03 pm

well.. that is only a part of the "story" :P . The details of the story was thought out by my group mates..

In the early earth, (a much earlier time when there was still no knowledge of it nowadays) the earth environment was divided into two hemispheres. The northern hemisphere is supportive of L-organism growth only and the southern is supportive of D-organisms only. This was due to the differences in genetic and metabolic mechanism between the two.
Neither one can survive in the other's environment. Thus, there was little transfer of gene between the two...

As for the meteor, it happened to hit the southern part and create such a huge impact that it annihilated all the D-organisms and most of the L-organisms.. The L-organisms that managed to adapt to the changes in earth environment (due to the meteorite impact) survived and the rest died.

I just thought of this:
*Perhaps the surviving L-organisms could be what the scientist called the LUCA (Last Common Universal Ancestor)*

haha.. i think it has become more like a story... :lol:

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Why L-AA

Post by pankaaj » Sun Jan 22, 2006 1:32 pm

Fitness is one of the very important thing in this part.
See ; was all the things happened simultaneously or not ? this also matters.
And i don't think that there is a huge difference in the environmental conditions on both the hemispheres. :shock:
( May be I'm wrong) :!:

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New Reason 4 Old Q.s

Post by cytochromeP » Sun Mar 19, 2006 2:19 pm

Hi hrushikesh,

Heres a brand new reason for the old problem - Why more L than D in biology ?

Link:
:arrow: http://www.newscientist.com/article/mg18925404.400

Chk it out ppl. 8)
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Post by Nite » Mon Mar 27, 2006 1:25 pm

hi cytochrome! :D

that's an interesting article! can you find the full text of the article?

followed yr link but it's only a summary of the article. did a search but din find the full text.. wuld like to noe more about it :D
Go as far as you can see, and when you get there you will always be able to see farther.

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