Life Is Left Handed?

[Lamron333]

Taken from: https://www.cfa.harvard.edu/~ejchaisson/cosmic_evolution/docs/fr_1/fr_1_chem4.html

A central puzzle in modern biochemistry is life’s chirality—that is, a tendency for life’s molecules to have a certain preferential orientation, or “handedness.” Much of life is said to be inherently left-handed, especially its amino acids. No one has ever been able to explain satisfactorily how life became so asymmetric. Yet broken symmetry seems as central to biology and life on Earth as it is to physics and matter in the early Universe. Asymmetry may well be an essential prerequisite for the origin and evolution of complexity throughout all of Nature.

Many molecules display two kinds of structures that are mirror images of each other. Their chemical formulas are the same in both cases, but the orientations of some of the molecules’ atoms are reversed left for right and right for left. For example, as shown in Figure 5.13, two forms of the alanine amino acid are possible; each is a mirror image of the other, much like our left and right hands are mirror images, as are the left- and right-handed wood screws also shown in the figure.
FIGURE 5.13



FIGURE 5.13 — Left-handed and right-handed screws (top) are in some ways analogous to the mirror-image arrangements of the atoms in simple molecules, such as those of the alanine amino acid shown here (bottom). In life as we know it, however, such molecules are constructed only in their left-handed configurations.

section snipped by mod, owing to copyright. See the link

 

The part that got me interested was:

Life’s amino-acid preference for left-handedness is particularly puzzling because such molecules,
when artificially produced in the laboratory, invariably show an equal mixture of left- and right-handed configurations.
(meaning we can't make just left or just right in the lab) Lamron333
Furthermore, should a right-handed amino acid drift into a living organism, the catalysts that control protein production will quickly destroy it.
Not only that, when a living organism dies and decays, thermal fluctuations change molecular shapes randomly,
so that eventually an even left-right mixture results.
Why terrestrial life employs only left-handed amino acids or right-handed nucleic acids is one of the great unsolved mysteries of chemical evolution.

 

 

Any Thoughts?

Edited March 4, 2015 by swansont
copyright

[Strange]

 

Why terrestrial life employs only left-handed amino acids or right-handed nucleic acids is one of the great unsolved mysteries of chemical evolution.

 

I have always assumed this was just chance. As you (*) say, molecules of the wrong chirality are not synthesized and are destroyed when encountered. It is a form of natural selection: once early life happened to use one form, then it was stuck with it. If it had been the other way round, the question would be the same. It is like tossing a coin once and then saying it is an unsolved mystery why you got heads not tails.

 

(*) I have just realised it wasn't you. Did you really need to copy the entire (copyrighted) page?

[Lamron333]

Yes I did provide the original material as a copy & posted the Original link. My question is more about how the cell recognizes left from right twist & how it knows what end is what? Like if the rotation was Right, would it start at the back(so to speak), of the DNA strand & work backwards or just fail all together? I'm not sure any of us knows what that does....

Edited March 3, 2015 by Lamron333

[studiot]

This book give the most fascinating story of the first use of chirality in explaining the poisoning of an entire town in Germany.

 

http://www.amazon.co.uk/Chasing-Molecule-Discovering-Building-Blocks/dp/0750933461

Edited March 3, 2015 by studiot

[CharonY]

First, please do not copy paste articles in their entirety (copyright infringement and all that). Second, the article is a bit misleading as organisms to produce amino acids and sugars with both chirality. They just use one. Enzymes such as racemases and epimerases change the molecules to the right configuration. Specific to the question, enzymes involved in building polymers such aminoacyl tRNA transferases (which load the tRNA with the cognate amino acids) only work with L amino acids, thus ensuring that only one type of peptide/protein can ever be formed.

If mutated it could in theory be transported to the ribosome, at which point the elongation of the peptide would be stalled by its presence.

[Wolfhnd]

Right-handed Amino Acids Help Bacteria Adapt

 

"In the overwhelmingly left-handed world of amino acids, the right-handed versions of a few such molecules act as signals that spur bacteria to adapt to changing conditions."

 

http://www.hhmi.org/news/right-handed-amino-acids-help-bacteria-adapt

[Lamron333]

First, please do not copy paste articles in their entirety (copyright infringement and all that). Second, the article is a bit misleading as organisms to produce amino acids and sugars with both chirality. They just use one. Enzymes such as racemases and epimerases change the molecules to the right configuration. Specific to the question, enzymes involved in building polymers such aminoacyl tRNA transferases (which load the tRNA with the cognate amino acids) only work with L amino acids, thus ensuring that only one type of peptide/protein can ever be formed.

If mutated it could in theory be transported to the ribosome, at which point the elongation of the peptide would be stalled by its presence.

#1, It's not a crime to have peer review of a published work.

#2, I never claimed it was my work & even provided the original link to the auther.

#3, I was asking a question based on such work to spark a disgussion we can all learn from.

And #4, Knoledge should always be shared for the greater good.

 

Good Day Sir!!!

 

I admit I didn't consider "tRNA", also what about epigenetics?

 

PS, same answer to you Strange

This book give the most fascinating story of the first use of chirality in explaining the poisoning of an entire town in Germany.

 

http://www.amazon.co.uk/Chasing-Molecule-Discovering-Building-Blocks/dp/0750933461

Thank you for pointing this out, just ordered it.

Right-handed Amino Acids Help Bacteria Adapt

 

"In the overwhelmingly left-handed world of amino acids, the right-handed versions of a few such molecules act as signals that spur bacteria to adapt to changing conditions."

 

http://www.hhmi.org/news/right-handed-amino-acids-help-bacteria-adapt

Also very interesting, lots of works to read through I like that though, keeps me busy.

 

I have always assumed this was just chance. As you (*) say, molecules of the wrong chirality are not synthesized and are destroyed when encountered. It is a form of natural selection: once early life happened to use one form, then it was stuck with it. If it had been the other way round, the question would be the same. It is like tossing a coin once and then saying it is an unsolved mystery why you got heads not tails.

 

(*) I have just realised it wasn't you. Did you really need to copy the entire (copyrighted) page?

It's a beautiful mystery & I want to know more on Why this rather than the other.

Edited March 4, 2015 by Lamron333

[studiot]

Since you are interested in Chirality, please not that the term covers more phenomena than just left v right handed -ness.

[Strange]

#1, It's not a crime to have peer review of a published work.

 

It is a crime to copy copyrighted material.

 

 

I want to know more on Why this rather than the other.

 

If life used right-handed chemicals you would be asking the same question. <shrug>

[StringJunky]

 

It is a crime to copy copyrighted material.

And bad manners. The author(s) won't have any idea of the interest their work generates if there is not some gentle nudge for readers to their site by leaving it incomplete at this end. Clicks matter.

[swansont]

!

Moderator Note

 

I have snipped a portion of the originally posted material. If you wish to read the entire article, go to the link. (For the record, no you can't just copy an entire article and post it)

 

Please discuss the bio/chem topic. Any further discussion of copyright must be brought up in another thread.

 

[CharonY]

 

 

I admit I didn't consider "tRNA", also what about epigenetics?

 

 

 

What about it? Why do you think does it have anything to do with chirality?. (Note that some people like to use the term because it sounds novel, which it isn't, but functionally it is "just" another layer of regulation.)

 

For about the rest, it is not about tRNA per se, but rather all the mechansims involved in polymerization. All of them recognize just one stereoisomer and that is where the specificity comes from. However, during regular metabolism, especially (but not exclusively) in prokaryotes routinely both isomers are produced. Further pathways allow their conversion, but disruption of these pathways can result in a change of the ratio of the isomers, As in the example of the link above and there are some more, this can be used by the cell in one way or another to sense some issues.

Edited March 4, 2015 by CharonY

[Endy0816]

Would it be possible to swap which type they recognize?

[CharonY]

Theoretically yes, and I believe for certain enzymes mutations in the active centers have resulted in loss in specificity in vitro. In addition, some transferases have found to be less specific with respect to non-naturally occurring stereoisomers of certain nucleotides.

If the goal is to e.g. create a protein using the stereoisomers it would be very difficult as it is a process requiring several proteins which are stereospecific. Chemically it should be possible, but it would be very, very difficult to realize.

[Endy0816]

Thanks. Gives some food for thought as to the possibility of building a working case study.

[mickeytea]

Heh, if anybody here's played MASS EFFECT, you might have overheard some Salarians discuss how they were handed levo instead of dextro protein shakes, or something like that. I don't exactly remember.