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| Pendragon |
 Posted: Tue May 06, 2008 10:39 am Post subject: Left-handedness of the molecules of life - chirality |
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Please correct me where I'm wrong 
I heard that all molecules of living organisms (or all molecules of a certain type?) are left-handed on earth, and that this probably came about by coincidence (it could've been right-handed as well). What I wonder is: would life have been different if by chance the molecules of living organisms had been right-handed rather than left-handed? Or is that like asking "would life have been different if organisms evolved to breath helium rather than oxygen?", with the obvious answer "there'd be no life" ? |
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| organic god |
| Posted: Tue May 06, 2008 10:50 am Post subject: |
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yeh i think you're on the right lines, the optical isomers of a compound can have/do have different properties from eachother and it would make a big difference to life.
im no biologist but isn't there something to do with optical isomerism in photosynthesis?
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| Scifor Refugee |
| Posted: Tue May 06, 2008 11:15 am Post subject: |
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| organic god wrote: |
yeh i think you're on the right lines, the optical isomers of a compound can have/do have different properties from eachother and it would make a big difference to life.
im no biologist but isn't there something to do with optical isomerism in photosynthesis? |
Usually for simple left/right chirality there is no difference in the chemical properties of the molecules, unless they are interacting with other chiral molecules. So you could easily switch everything to run on R isomers instead of S isomers, and so far as I know everything would work the same. |
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| SteveF |
| Posted: Tue May 06, 2008 12:19 pm Post subject: |
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Scifor is correct. Our terrestrial organisms evolved with l-amino acids and d-glucose, but an early coin flip would have easily sent everything the other way. There would be no difference in the final product. We'd all arrive at this point looking and behaving exactly as we do now.
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| Pong |
| Posted: Tue May 06, 2008 11:24 pm Post subject: |
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| Thinking with my stomach: would these organisms be tasty, or like old rubber bands and pennies, to us? |
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| sunshinewarrior |
| Posted: Wed May 07, 2008 7:42 am Post subject: |
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| SteveF wrote: |
Scifor is correct. Our terrestrial organisms evolved with l-amino acids and d-glucose, but an early coin flip would have easily sent everything the other way. There would be no difference in the final product. We'd all arrive at this point looking and behaving exactly as we do now.
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On the other hand, surely some proteins and enzymes etc are specific enough in their activity to require specific chirality?
All I know about this I got from Chirs McManus' Left Hand Right Hand, always a souce of fascination for sinistrals like me, and with a lovely tale of tell of asymmetry coming up through the universe all the way from the weak nuclear force... |
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| raed |
| Posted: Wed May 07, 2008 7:53 am Post subject: |
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scifor is partially right
u mentioned d-glucose as an example
glucose is taken by the cell and oxidized to produce energy , So there will be no difference d or l
but compound wich interact with enzymes or receptors must have specific configuration e.g : Insulin , dopamine.
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Raed Ahmed Shalaby
Dont let MEDIA affect you , You have a brain !
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| SteveF |
| Posted: Wed May 07, 2008 7:56 am Post subject: |
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| Quote: |
| On the other hand, surely some proteins and enzymes etc are specific enough in their activity to require specific chirality? |
Also correct, Lefty. But the entire biological system would be mirror-imaged -- enzymes, substrate, and all. Same results, and neither us nor them would know until we checked some solutions for optical activity... or figured out why their Big Macs are indigestible to us and vice versa.
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| sunshinewarrior |
| Posted: Wed May 07, 2008 8:37 am Post subject: |
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| SteveF wrote: |
Also correct, Lefty.
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Heh. 
Ta. |
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| Scifor Refugee |
| Posted: Wed May 07, 2008 10:01 am Post subject: |
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| raed wrote: |
scifor is partially right
u mentioned d-glucose as an example
glucose is taken by the cell and oxidized to produce energy , So there will be no difference d or l
but compound wich interact with enzymes or receptors must have specific configuration e.g : Insulin , dopamine. |
That's why I said that there is no difference unless they are interacting with other chiral molecules. |
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| Pong |
| Posted: Wed May 07, 2008 10:53 am Post subject: |
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| their Big Macs are indigestible to us and vice versa. |
It's war then. We meet E.T. first thing I'll ask is "left or right?" Can we shake hands? Which side are you on? |
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| Pendragon |
| Posted: Wed May 07, 2008 11:04 am Post subject: |
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| Thanks for the info! I can't really contribute to the discussion, but I'm watching and learning |
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| Ophiolite |
| Posted: Wed May 07, 2008 11:28 am Post subject: |
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There is a hypothesis that the handedness is a result of some side effect of the weak nuclear force. It seems not to be a popular explanation, but it has not yet been refuted. I have only the dimmest recollection of this and no references.
Others have tried to explain the handedness that actually exists as preferential formation on crystals or clay particles. There have been other, exotic explanations as well. I am never comfortable with explanations that run 'that's just the way it is'. They may be correct, but if we accept that position blindly then we may miss something significant.
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| raed |
| Posted: Wed May 07, 2008 11:59 am Post subject: |
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| Ophiolite wrote: |
There is a hypothesis that the handedness is a result of some side effect of the weak nuclear force. It seems not to be a popular explanation, but it has not yet been refuted. I have only the dimmest recollection of this and no references.
Others have tried to explain the handedness that actually exists as preferential formation on crystals or clay particles. There have been other, exotic explanations as well. I am never comfortable with explanations that run 'that's just the way it is'. They may be correct, but if we accept that position blindly then we may miss something significant. |
I Cant actually understand ur words , Handedness or chirality is simply due to probability of positions of bonds , and that what make compounds chiral and others are achiral
In case of symmetric compounds , if u draw the probabilities of positions of bonds we will obtain the same molecule configuration
But in chiral molecules , if u do so will have 2 mirror image like ur 2 hands.
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Raed Ahmed Shalaby
Dont let MEDIA affect you , You have a brain !
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| Ophiolite |
| Posted: Wed May 07, 2008 12:26 pm Post subject: |
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Forum Radioactive Isotope
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I should have written that the preference in biological molecules for a particular handedness may not be a matter of chance, but could have been determined by some property of the environment (surface chemistry for example) or of the constants/forces of nature (for example the role of the weak force).
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