Reason for one chiriality in biology

  • #1
515
9
We know that DNA and other biological molecules have only one chiriality of two possible. Is here any explanation of this or any speculations about this?
 

Answers and Replies

  • #2
mjs
16
2
I think this is debatable. Probabably it reflects their common origin.

This is a fascinating topic because stereotactic conformations provide the 3D complexity needed to avoid equillibrium and thus, to allow life exist in the first place and sustain itself.
 
  • Like
Likes exponent137
  • #3
Drakkith
Staff Emeritus
Science Advisor
21,102
4,933
There are certainly some ideas of how and why homochirality exists. See this article for example (abstract below): http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2857173/

Abstract
The single-handedness of biological molecules has fascinated scientists and laymen alike since Pasteur's first painstaking separation of the enantiomorphic crystals of a tartrate salt more than 150 yr ago. More recently, a number of theoretical and experimental investigations have helped to delineate models for how one enantiomer might have come to dominate over the other from what presumably was a racemic prebiotic world. This article highlights mechanisms for enantioenrichment that include either chemical or physical processes, or a combination of both. The scientific driving force for this work arises from an interest in understanding the origin of life, because the homochirality of biological molecules is a signature of life.
 
  • Like
Likes exponent137
  • #4
314
162
I think it is much simpler than that. My pet theory is that homochirality stems from the intrinsic angular momentum of the earth spinning on its axis. This angular momentum favored one chirality over the other in the primordial soup.
 
  • Like
Likes exponent137
  • #5
Drakkith
Staff Emeritus
Science Advisor
21,102
4,933
I think it is much simpler than that. My pet theory is that homochirality stems from the intrinsic angular momentum of the earth spinning on its axis. This angular momentum favored one chirality over the other in the primordial soup.
What possible connection could there be between the angular momentum of the Earth and the chirality of individual molecules?
 
  • #6
314
162
Perhaps the proto amino acids "felt" the angular momentum of rotation, and for that reason assumed the leverorotatory configuration as a result.
 
  • #7
Drakkith
Staff Emeritus
Science Advisor
21,102
4,933
Perhaps the proto amino acids "felt" the angular momentum of rotation, and for that reason assumed the leverorotatory configuration as a result.
Unless you have a reference that backs this up somehow then I'm afraid we can't discuss it. We don't allow personal theories here at PF.
 
  • #8
314
162
Unless you have a reference that backs this up somehow then I'm afraid we can't discuss it. We don't allow personal theories here at PF.
I looked for references, but apparently nobody knows exactly the angular velocity of the earth 3.8 billion years ago when coacervates were forming in the primordial seas. The only thing we can say for sure, it was greater then than today. For certain, the day was 22 hours long in the precambrian, about 500 million years ago. If we can't discuss it so be it.
 
  • #9
Fervent Freyja
Gold Member
653
694
We know that DNA and other biological molecules have only one chiriality of two possible. Is here any explanation of this or any speculations about this?
D-sugars tend to be right-handed, while L-amino acids left-handed. I have read possible causes: 2nd law of thermodynamics affecting early molecular processes, asymmetrical physical laws (electroweak interaction), earths rotation, and it goes on and on.
 
  • Like
Likes exponent137
  • #10
10
1
Disclaimer - I am not a chemist or biologist. I have a physics B.Sc and what I know about biology is only because I read a little bit about everything.

I tried but failed to find a link to a page I read long ago about how chirality affects the way proteins fold, how DNA twists, etc. I think - but am not nearly sure - that I got led to that page from a page about thalidomide. However, the simple fact that chirality affects folding implies that chirality affects how molecules work ... and if they don't work properly that in turn implies that the process polices itself by discarding that which does not work.

In case the above wasn't clear enough, suppose that during the assembly of a protein one of the molecules used as building bricks has left and right chirality. If the assembly process takes up a left chiral building block the protein will fold correctly. If it takes up a right chiral building block it will not fold correctly ... and that either halts the assembly process or results in a defective protein that is discarded.
 
  • Like
Likes exponent137
  • #11
Ygggdrasil
Science Advisor
Insights Author
Gold Member
3,235
3,312
Here's a nice news piece from the Royal Society of Chemistry on why homochirality is important: http://www.rsc.org/chemistryworld/2015/10/origin-homochirality-life-asymmetry
The presence of carbon atoms with four chemically distinct substituents leads to chiral molecules, with non-superimposable mirror image forms known as stereoisomers. In any chemical synthesis, without intervention, an almost equal or racemic mixture of left- and right-handed molecules will form. So where did our homochiral world come from?

Donna Blackmond from the Scripps Research Institute in California, US, has been tackling the question. She says there is a rationale for why homochirality might offer a survival advantage. Chirality is important for creating complex systems with varied forms of molecular recognition and selectivity – both of which are crucial in life. Blackmond says when she gives talks to children, she uses a handshake to explain these concepts. ‘We shake hands and then I say “Let me try this with my left hand and your right hand” – and that doesn’t work very well. Left and right doesn’t make the same handshake or give the same message.’
That simple analogy refer to the concept of enantiomeric cross-inhibition (also the term for the idea expressed in the above post), and origin of life researchers have been thinking about how such obstacles might have been overcome duirng abiogenesis.
 
  • Like
Likes jim mcnamara, exponent137 and Fervent Freyja
  • #12
Fervent Freyja
Gold Member
653
694
Here's a nice news piece from the Royal Society of Chemistry on why homochirality is important: http://www.rsc.org/chemistryworld/2015/10/origin-homochirality-life-asymmetry
Another article I found after that one.

The wording, "On the back of a comet...", just :)) :DD :H!

"Why is everyone’s DNA right-handed?’ asks Tim Gay from the University of Nebraska–Lincoln, US. Two theories have been proposed in answer to this question. The first idea is that homochirality came to Earth from space on the back of a comet..."
 
  • Like
Likes exponent137
  • #13
Fervent Freyja
Gold Member
653
694
I looked for references, but apparently nobody knows exactly the angular velocity of the earth 3.8 billion years ago when coacervates were forming in the primordial seas. The only thing we can say for sure, it was greater then than today. For certain, the day was 22 hours long in the precambrian, about 500 million years ago. If we can't discuss it so be it.
Yeah, difficult to find, but some not-entirely-credible sources say a 2.5 hour day at around 4 billion years, but others 6 hour days.

We need a better understanding on how the earth and moon have interacted throughout history in order to also gain a better understanding of the formation of life on earth (and determine that angular velocity). Prior generations of biologists weren't taught enough mathematics to make those calculations. They are waiting on astronomers and physicists to help out.
 
  • Like
Likes exponent137
  • #14
314
162
One way to check if angular momentum could cause homochirality is to reproduce Miller's experiment in a reaction vessel spinning at high rpm. Let the experiment play out long enough to see if it is time dependent as well. If there is an entantiomeric escess, then the theory could hold water.
 
  • #15
Drakkith
Staff Emeritus
Science Advisor
21,102
4,933
Again, unless someone can find a reference that suggests a method by which homochirality is due to a fast-spinning Earth, I ask that the idea not be brought up again. Further posts on it will be removed unless they contain a valid reference.
 
  • #16
5
3
I don't think we need theories to explain chiral exclusivity. I think someone should put forth a theory proving it was even reasonably possible to NOT have chiral exclusivity. Isn't it possible that there was no compelling reason for left vs right when we already are surrounded by compelling proof that having one "preference" or another is what allows life to exist as we know it? As the processes creating life evolved, eventually a process arose that was so complex, it would not continue without some inherent chirality. We know this is true because such conditions exist within our own biochemistry. Whichever chirality random luck gave at the time or the origin of a single form of actual life (or even before), that was the one to continue. We all like explanations, but we should remember what seems weird is sometimes what really should be expected. How could you NOT expect exclusive chirality from a single starting point of evolution when the complexity of life eventually demands chiral preference?
 
  • #17
Drakkith
Staff Emeritus
Science Advisor
21,102
4,933
We all like explanations, but we should remember what seems weird is sometimes what really should be expected. How could you NOT expect exclusive chirality from a single starting point of evolution when the complexity of life eventually demands chiral preference?
If it is expected, then there needs to be a reason why. And that requires a theory.
 
  • #18
Vanadium 50
Staff Emeritus
Science Advisor
Education Advisor
26,358
9,841
Again, unless someone can find a reference that suggests a method by which homochirality is due to a fast-spinning Earth, I ask that the idea not be brought up again.
The idea is DOA. It would predict opposite chiralities in the nothern and southern hemispheres.

While there is some evidence that there is an advantage to homochirality, as far as I know there is nothing but speculation on why or even if the handedness on Earth is more advantageous than the opposite one.
 
  • Like
Likes Drakkith
  • #20
TeethWhitener
Science Advisor
Gold Member
1,931
1,357
The idea is DOA. It would predict opposite chiralities in the nothern and southern hemispheres.
It would also predict that if you did a chemical reaction in the lab which produced a chiral center, you could get different enantiomeric enrichments depending on which way the stirbar in your flask was rotating.
 
  • #21
TeethWhitener
Science Advisor
Gold Member
1,931
1,357
Here we go. In section 1.4.1, the author talks about vortex motion and gives references to experiments testing @Kevin McHugh 's theory. It's certainly quite far-fetched, but consider: plenty of chiral systems exhibit separation by enantiomers (e.g., in crystallization, oligomerization, etc.). Presumably, larger structures are more influenced by large scale vortex motion than smaller structures (because of their lower rotational diffusion coefficient). As for the northern/southern hemisphere objection: the Earth has had 4 billion years of geological and hydrological mixing of hemispheric contents, so it's not clear that the objection holds much water.

I personally buy into the idea that homochirality arose from an autocatalytic system that underwent symmetry-breaking into a certain configuration. It's been observed in the lab (many times), and I think it's far more likely than speculative processes that "rob" chirality from either large scale rotations or the nuclear weak force. But other ideas have their merits, especially when they lead to falsifiable claims.
 
  • #22
515
9
The idea is DOA. It would predict opposite chiralities in the nothern and southern hemispheres.

While there is some evidence that there is an advantage to homochirality, as far as I know there is nothing but speculation on why or even if the handedness on Earth is more advantageous than the opposite one.
I think that you are wrong. Chiralities in the nothern and southern hemispheres were not be different!

But the question is, if this slow spinning of earth is fast enough to give any effect.

Except, if you think that rotation of earth cause different rotations of water in northern and southern hemisphere, ant that this rotation is primary more important than rotation of earth.
 
Last edited:
  • #23
Vanadium 50
Staff Emeritus
Science Advisor
Education Advisor
26,358
9,841
I think that you are wrong. Chiralities in the nothern and southern hemispheres were not be different!
I was going to respond in detail, asking you to consider whether the chirality would flip if the earth were spinning the other way, or if it were upside down, and so on. But it's your personal theory, and you can abandon as much actual science as you would like in crafting it. Just don't expect other people to take it seriously.
 
  • #24
515
9
I was going to respond in detail, asking you to consider whether the chirality would flip if the earth were spinning the other way, or if it were upside down, and so on. But it's your personal theory, and you can abandon as much actual science as you would like in crafting it. Just don't expect other people to take it seriously.
This about influence of rotating earth is not my theory, but of Kevin McHugh.
About mechanism for it I do not know, and about how relatively very slow rotating earth can have any influence, I also do not understand.
I am only think that influence of rotating earth is the same in northern or in southern part of earth. Except if secondary influences are important, these are rotation of water in north or in south. Or what do you think with your: "It would predict opposite chiralities in the nothern and southern hemispheres."
 

Related Threads on Reason for one chiriality in biology

  • Last Post
Replies
5
Views
3K
  • Last Post
2
Replies
39
Views
25K
  • Last Post
Replies
4
Views
3K
Replies
1
Views
3K
  • Last Post
Replies
5
Views
5K
  • Last Post
Replies
1
Views
609
  • Last Post
Replies
18
Views
4K
Replies
4
Views
2K
  • Last Post
Replies
6
Views
4K
Top