Biology Forum Molecular Biology Why only L-AAs

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    • #3086

      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.


    • #36570

      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: … ality.html … estion.htm … .Bc.r.html

    • #36576

      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…

    • #36714


      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.

    • #36928

      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?

    • #37083

      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??? 😀
      Really cool… is this hypothisis cheched ???

      Yours biolover[ not by chance!!!]

    • #37597

      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..

    • #37751

      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?

    • #37853

      well.. that is only a part of the "story" 😛 . 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… 😆

    • #38113

      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. 😯
      ( May be I’m wrong) ❗

    • #43727

      Hi hrushikesh,

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


      Chk it out ppl. 8)

    • #44371

      hi cytochrome! 😀

      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 😀

    • #44434

      well, basically the article in New Scientist say that water protect the L-amino acid.
      three quarter of water consist of ortho h2o, a slightly magnetic molecules and
      one quarter non-magnetic para h2o.
      this weak force causes the L amino acid to be slightly magnetic meaning it interact more readily with magnetic ortho h2o
      therefore L amino acid is more stable

    • #44812

      Thanks cyto…
      thanks kiekyon…
      really something valuable…

      samilar q now…why 3/4 ortho h2o and only 1/4 para…

      sorry for my irritating Qer nature if it seems…


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