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Topic: Why does nature produce only one isomer?  (Read 9738 times)

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Offline chunhan90

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Why does nature produce only one isomer?
« on: October 06, 2009, 07:50:18 AM »
My professor taught us that in nature only one kind of isomer exist, but didn't tell us the reason and why so. Is there anyone that knows why this happens??

Offline Borek

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Re: Why does nature produce only one isomer?
« Reply #1 on: October 06, 2009, 07:57:38 AM »
This is not true as stated. Please elaborate.

My bet is that you are thinking about D&L aminoacids, but even then it is not entirely true.
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Offline typhoon2028

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Re: Why does nature produce only one isomer?
« Reply #2 on: October 06, 2009, 11:02:09 AM »
My biochemistry is weak.

I believe a common example to what you are talking about can be found if you research glucose.

d-glucose can be used by the body for energy
l-glucose cannot be metabolized.

This commonly referred to as left and right handed sugar.

My limited understanding is d-glucose converted to energy via a cycle.  This first step involves an enzyme called hexokinase.  l-glucose cannot react with hexokinase.  Hexokinase is a large protein (think 3-dimentionally) and the d-glucose has to fit into the protein to react.  I think of it as trying to fit your hand into a baseball glove.  Wrong hand in the glove and you can't catch the baseball.


Offline chunhan90

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Re: Why does nature produce only one isomer?
« Reply #3 on: October 06, 2009, 03:55:15 PM »
The example shown in my textbook is a cancer drug called taxol, which is rich in stereochemistry. The question asks why nature only creates one type of isomer(more specifically stereoisomers).

Offline cth

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Re: Why does nature produce only one isomer?
« Reply #4 on: October 06, 2009, 04:32:40 PM »
Considering that DNA is chiral (helicoidal chirality), I don't think it is so surprising after all that only one stereoisomer is metabolised for organic molecules. The very bricks of our entire body are chiral. Never thought of yourself as a huge pile of chirality?!  ;D

But I don't think anyone really knows why DNA is the way it is.


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I think of it as trying to fit your hand into a baseball glove.  Wrong hand in the glove and you can't catch the baseball.

Nice illustration.  ;)

When you think the structure of DNA was discovered in the 1950s, those guys were good! And no computer to help in the task at the time.  :o

Offline alphahydroxy

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Re: Why does nature produce only one isomer?
« Reply #5 on: October 06, 2009, 05:13:38 PM »
This is not true as stated. Please elaborate.

My bet is that you are thinking about D&L aminoacids, but even then it is not entirely true.

:D Give the guy a break, you know what he means!


To the OP: This is one of the big questions, along with "How did life emerge?" etc.

Tha fact of the matter is, no one really knows why nature often favours a particular chiral arrangement,

it is because it was

There are a number of theories to why it is this way. A popular line of reasoning goes (very vaguely) like so:

From a racemic mixture, a 'symmetry breaking event' occured, resulting in a slight excess of one isomer. Then, a process of 'chiral amplification' increased the relative amount of that isomer, and 'chiral tranmission' allows the transfer of this chirality from one set of molecule to another.

This ia largely speculative reasoning, although there is experimental evidence to back up these claims to a certain degree (no refs to hand I'm afraid, though I seem to remember a paper in nature from perhaps 2004-2005).

While this doesn't really answer your question, it might give you something to look into further should you be so inclined...




Offline chunhan90

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Re: Why does nature produce only one isomer?
« Reply #6 on: October 07, 2009, 02:10:16 AM »
Thank you all for the replies, I just thought there would be a scientific process in which it creates this phenomenon. I didn't realize how "big" my question was :)

Offline gfunk

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Re: Why does nature produce only one isomer?
« Reply #7 on: October 07, 2009, 02:13:00 AM »
My professor taught us that in nature only one kind of isomer exist, but didn't tell us the reason and why so. Is there anyone that knows why this happens??
Not necessarily.  For example, there's (+/-)-carvone.  One enantiomer is spearmint, the other is caraway.

The example shown in my textbook is a cancer drug called taxol, which is rich in stereochemistry. The question asks why nature only creates one type of isomer(more specifically stereoisomers).
What is the molecular machinery that creates these secondary metabolites?  Remember, chirality must rise from chirality.  Therefore, to make a chiral molecule, it must be made in a chiral environment.

Never thought of yourself as a huge pile of chirality?!  ;D
But I possess a plane of symmetry!  ;)

(no refs to hand I'm afraid, though I seem to remember a paper in nature from perhaps
Don't believe anything in Nature!  :o
Grad Student - Organic Chemistry
University of Alberta

Offline Borek

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Re: Why does nature produce only one isomer?
« Reply #8 on: October 07, 2009, 04:33:46 AM »
But I possess a plane of symmetry!  ;)

Do you? Urban legend :)

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Don't believe anything in Nature!  :o

Much better source than many others.
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Offline gfunk

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Re: Why does nature produce only one isomer?
« Reply #9 on: October 07, 2009, 10:21:23 AM »
But I possess a plane of symmetry!  ;)

Do you? Urban legend :)

Well, to some degree!  :D

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Quote
Don't believe anything in Nature!  :o

Much better source than many others.

Well, I guess it depends on what you're looking for.  And what journals you're comparing it to.
Grad Student - Organic Chemistry
University of Alberta

Offline Borek

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Re: Why does nature produce only one isomer?
« Reply #10 on: October 07, 2009, 10:58:56 AM »
And what journals you're comparing it to.

Perhaps not to JACS, but it is still a peer reviewed journal with impact factor around 30, so I would not dismiss it lightly.
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