Chirality

doctoro
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Chirality

It is a fact that most, if not all organisms on this planet contain molecules in their bodies that assume the L-enantiomer exhibiting the property of chirality.  I will not bother to explain this for non-scientists.

An evolutionary argument is this:  If God intelligently designed life, why choose the L-enantiomer, why make enantiomers and the first place, and why wouldn't you have some animals that were made of the D-enantiomer?

My question is this:

Is it possible that life evolved in different places on the Earth simultaneously?  That is, is it possible that all life did not evolve from primeval soup in the same place?  Maybe there were many ponds of primeval soup in different places?

To test this experimentally, I wonder if there are organisms -- bacteria in thermal ocean vents and inhospitable climates that contain chemicals in the D-enatiomer form.  If there are strange critters on our own planet with these D-enantiomers feeding off chemicals in ocean vents and such, it might lend credence to the idea that there were multiple points for the origin of life, that the primeval soup theory proposed by Oparin has some weight, and the probability of abiogenesis is higher than previously thought. 


Yellow_Number_Five
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I actually use chirallity,

I actually use chirallity, and it's uniformity as part of one of my "Questions for Creationists" stickied in this thread.

It is very interesting that ALL life on earth (including the exotic forms you mentioned), so far as we know, uses the SAME chirality. There really is no good reason for this from a "design" standpoint - any chirality could have worked equally well, and it certainly is not self-evident that L-twist is any better than any of the other 15 possibilities for nucleic acid polymers.

It's always been explained in evolutionary biology circles that such things are indicative of a common ancestor, and thus far, that is certainly the most plausible explanation.

Were we to find some bug deep in the ocean or deep in the earth, it would be a real "WOW!" moment. It would certainly mean that there were very early and distinct splits from the beginning of life on earth, or perhaps that life sprang up in slightly different ways in different places, or that life may have been introduced to earth from elsewhere, etc. You can also be sure that creationists would cite it as proof of "special creation".

Such a discovery would certainly rock the boat, and while I'm a bit skeptical of such, it is not outside of the realm of possibility.

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Mjhavok
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Hello,

Hello,

When I seen that you had stated the L Isomer is more prevalent in nature I thought that I remember this was wrong. I post below an excerpt from class notes.

"D and L isomers which comes from the Latin for left (levo)rotary and right (dextro)rotary are called enantiomers.


Enantiomers are isomers that differ in spatial arrangement around an asymmetrical carbon. The D and L isomers of glucose for example are in effect mirror images of each other that cannot be superimposed on each other. In a straight chain structural diagram of Glucose you determine if it is D or L glucose by the position of the hydroxyl group on the 5th carbon from the carbonyl group end of the molecule. If it is projecting out to the right of the carbon it is D-Glucose (dextrose) and if it is to the left it is L-Glucose. In nature most molecules are D isomers. Another way of looking at it is that the carbon you look for the the penultimate carbon when counting down from the carbonyl group and on this carbon whether the OH is on the left or right side determines if it is D or L


A cell can differentiate between these isomers. 1 is usually active and other inactive.


In nature, there is a preference for D monosaccharide isomers. D-Glucose for example is broken down in the human body to eventually provide energy for the cells in the form of ATP. This can be stored as glycogen for use at later time or for a quick energy boost.


L isomers are not recognized as substrates by many metabolic enzymes and therefore won’t be broken down and use in the body by them. One example is the enzyme permease which is very specific and can tell the difference between optical isomers of glucose. This is why sweeteners for diet type drinks work. They are diet because they contain a form of sugar or sugar substitute that isn’t used in the body.


L isomers in the body possibly could cause some competitive inhibition with the normal substrate of an enzyme. If the enzyme is blocked by a molecule with different chirality the actual substrate will not be able to bind with it.


One health implication in the body is that L isomers aren't metabolised by bacteria in the mouth as well as not being metabolised by humans. This means that they would not get there veritable feast of glucose when the L isomers are consumed and this would help to prevent tooth decay from chemicals bacteria release. Another health implication is weight loss, there are hundreds of chemicals with artificial sweeteners that the body doesn't metabolise because is it in the L Isomer form. This gives the L isomers a lower calorific value as the body can't metabolise them and store them. Lastly these isomers could help diabetics as they would not increase blood glucose levels."

It is late and I don't have time to go get my biochemistry textbooks to check this as it was a over a year ago I typed up this stuff and I could have been mistaken. I will do when I get up in about 5-6 hrs.

Ok I couldn't wait so I did a quick  check in a textbook (Lehninger's Princples of Biochemistry 4th Edition). It turns out that certain molecules seem to be different in the amounts of L and D configurations. Amino acids are mainly L isomers with a few D isomers in small peptides. Sugars are mainly D isomers. The D and L configuration is insufficient because many molecules aren't strictly D or L so the RS system is used.


Anyway good topic. Made me go back and look at some old stuff. I should do that over the holidays I think. Try and re-learn and remember stuff from 1st year.

I need sleep now :-S

"For me, it is far better to grasp the Universe as it really is than to persist in delusion, however satisfying and reassuring. "
- Carl Sagan

"Tantum eruditi sunt liberi"

"We are all in the gutter, but some of us are looking at the


doctoro
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Thanks MJ and Yellow5.  I

Thanks MJ and Yellow5.  I didn't think I'd get a response on this one.

 I would concede that I'm probably wrong about the exclusivity of the L isomer in nature.  It would seem that I overgeneralized the preferential treatment of L-peptides to be all-inclusive for all biochemistry.

 BUT;

I think this raises an interesting question despite the fact that I was wrong.  EVEN IF there is a preference for one chirality over the other in some biochemical reactions, it would stand to reason that one could study biochemistry throughout the biological kingdoms in order to classify evolutionary similarities and create phylogenetic trees. 

In fact, I'm sure modern evolutionary biologists already use this method.  If I remember back to my organismal biology class in college, I think that taxonomists make tables containing traits and tally up similar traits for different organisms to ascertain the degree of relationship.  If I remember correctly, I think that next to primates, PIGS have some of the most common DNA to humans...  That kind of astonished me.

 But back on topic...  I think the base of my question here is if it would be possible to find any proof in any organisms on Earth on a biochemical level that would lend credence to the possibility that life evolved from MORE than one common ancestor.  Suppose we had one primordial soup pond in China and one in Africa, both independently deriving life that evolved in different ways.  Perhaps that's just pure silly nonsense.  I really have no evidence to back up that theory...  But philosophers like Karl Popper imply that the best way to prove current theories is to test them constantly with alternatives.

 I know that when I studied immunological function, we spent some time talking about the blood complement cascade and its evolution in the animal kingdom.

The idea that life sprung from one microbial ancestor, an ADAM bacterium, if you will...  is kind of an awesome concept to wrap your mind around.  The skeptic and curious child in me, I think, wants to entertain alternatives just for entertainment.  

I think the crushing blow to my theory is probably DNA.  All organisms on Earth have DNA.  It would be pretty hard to conceive of DNA arising from independent locations on Earth.

What would be amazing is to find an alien life form with an alternative to DNA.  Dig up some meteorites and lets go to work! 


Mjhavok
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Also mixtures can racemise

Also mixtures can racemise to be 50/50. It can sometimes take a very long time though. To long to occur in the body really.

 

Check this http://en.wikipedia.org/wiki/Racemic 

"For me, it is far better to grasp the Universe as it really is than to persist in delusion, however satisfying and reassuring. "
- Carl Sagan

"Tantum eruditi sunt liberi"

"We are all in the gutter, but some of us are looking at the