Unsolved Problems in Reef Chemistry #1 Snail Shell Coiling

[Hiachi20]

The coriolis effect. Have you checked a snail below the equator?

Please don't tell me it matters does it lol

 

[Scott Weinrich]

I would like to mention the golden rule if someone hasn't already

Sorry if am coming off as a jerk. I really enjoy engaging in discussions like this. In my world, skepticism is often advantageous and I often find myself as the devil's advocate.

 

[Hiachi20]

Sorry if am coming off as a jerk. I really enjoy engaging in discussions like this. In my world, skepticism is often advantageous and I often find myself as the devil's advocate.

Oh you're fine I meant the coriolis mattering not the discussion. I thought you were saying they were different below the equator. I haven't read the whole post I just wanted to put in my two cents. Be skeptic. Let the others cure ich with garlic and a wooden stake

 

[Scott Weinrich]

I think you are making a big assumption that only a fully opposite enantiomer will induce a shift to the only other form available. Like a knife balanced on an edge, it must fall one way or the other. What pushes it one way need not be the exact opposite chemistry of what pushes it the other.

Upon further thought, I guess it would be possible to induce opposite chirality in a protein through a mutation that didn't change the chirality of any individual residue, but still affected the tertiary/quaternary structure. I'm still skeptical that is driving snail chirality though.

 

[Randy Holmes-Farley Verified Community Expert]

I am not making that assumption. If we are talking about proteins, then basically all amino acids have the same orientation. How is an opposite chirality protein going to be consistently produced when it relies on a point mutation of an opposite chirality amino acid? There would need to be a unique codon for the opposite enantiomer. I am not aware of unique codon for specific enantiomers of amino acids.

I didn't claim an opposite chirality molecule is produced. I claimed a different protein conformation is produced, and the mutant conformation tips the balance toward one chirality rather than the other. Maybe the simple absence of the protein at the critical site tips the balance.

In any case, the current literature, while not molecularly proving exactly how it works, considers that molecule to cell to organism propagation of chirality is a possibility thay are endeavoring to understand, and perhaps the most likely process.

 

[Randy Holmes-Farley Verified Community Expert]

FWIW, in the context of looking through these issues, I ran across a very interesting paper summarizing one of the great issues in molecular biology: how did it initially arise that all organisms use the same chiral molecules and none use the opposite chirality?

There's no reason all the life forms on earth should use the opposite chirality amino acids, sugars, etc. But they all use one kind. Why? How can that even happen?

Here's the discussion in a journal of the Royal Society of Chemistry:

https://www.chemistryworld.com/feature/the-origin-of-homochirality/9073.article

 

[madweazl]

When I see posts like this, it makes me wonder what is wrong with my brain that I don't even consider why a snail shell coils one direction vs the other LOL.

 

[JoshuaRock]

I loved this post. I was only able to read every 4th word or so but I couldn’t stop reading the whole thing. Things like this are interesting. Like did Adam and Eve have belly buttons.

 

[Randy Holmes-Farley Verified Community Expert]

When I see posts like this, it makes me wonder what is wrong with my brain that I don't even consider why a snail shell coils one direction vs the other LOL.

lol

It's a puzzle hiding in plain sight.

 

[Randy Holmes-Farley Verified Community Expert]

I loved this post. I was only able to read every 4th word or so but I couldn’t stop reading the whole thing. Things like this are interesting. Like did Adam and Eve have belly buttons.

lol

I'll have to leave that question to our owner and resident pastor.

@revhtree

 

[Scott Weinrich]

I didn't claim an opposite chirality molecule is produced. I claimed a different protein conformation is produced, and the mutant conformation tips the balance toward one chirality rather than the other. Maybe the simple absence of the protein at the critical site tips the balance.

In any case, the current literature, while not molecularly proving exactly how it works, considers that molecule to cell to organism propagation of chirality is a possibility thay are endeavoring to understand, and perhaps the most likely process.

Maybe our positions aren't that different then. I thought you were originally implying that chirality on a tissue-level has to arise from chirality on a molecular level. I took this to mean that the chirality of one or more biomolecules was dictating the chirality of the tissue. What you describe above could be consistent with an intercellular signalling scheme from which chirality can arise, e.g. presence/absence of a biomolecule.

 

[Randy Holmes-Farley Verified Community Expert]

Maybe our positions aren't that different then. I thought you were originally implying that chirality on a tissue-level has to arise from chirality on a molecular level. I took this to mean that the chirality of one or more biomolecules was dictating the chirality of the tissue. What you describe above could be consistent with an intercellular signalling scheme from which chirality can arise, e.g. presence/absence of a biomolecule.

Well, I am not seeing a way that cell chirality (or any higher order chirality) could arise without being caused by something that is itself already chiral or has some chiral recognition properties (like Pasteur seeing different oriented crystals and separating them by hand), and molecules are the only thing I know of that would provide this naturally.

The last paper I linked goes into substantial depth about how hard it is to get molecules to be spontaneously chiral, and I expect the exact same concern apply to higher order structures.

 

[Scott Weinrich]

Well, I am not seeing a way that cell chirality (or any higher order chirality) could arise without being caused by something that is itself already chiral or has some chiral recognition properties (like Pasteur seeing different oriented crystals and separating them by hand), and molecules are the only thing I know of that would provide this naturally.

The last paper I linked goes into substantial depth about how hard it is to get molecules to be spontaneously chiral, and I expect the exact same concern apply to higher order structures.

Why don't you think that intercellular messaging couldn't break chiral symmetry? Stem cells are constantly differentiating to form specific tissue structures that are asymmetric. Must every one of these differentiation events be dictated by the chirality of a biomolecule? A concentration gradient across a particular cell axis breaks symmetry in one direction. Add a couple more concentration gradients along different axes and it seems reasonable that a chiral structure could arise from signalling alone. The structures themselves may not have to be chiral if the rules for the signalling are "chiral".

Interestingly, the following paper finds left-handed chirality developing despite no chirality existing after the third division (which they determine to be the critical determinant of subsequent shell chirality). A chiral formation of cells after the third division yields right handed snails.

https://academic.oup.com/icb/article/54/4/677/2797866

They make a pretty fairly solid case for chirality arising from the chirality of biomolecules. In my eyes, they still fall a bit short of proving it though and they seem careful to phrase their results as such.

 

[Randy Holmes-Farley Verified Community Expert]

Why don't you think that intercellular messaging couldn't break chiral symmetry? Stem cells are constantly differentiating to form specific tissue structures that are asymmetric. Must every one of these differentiation events be dictated by the chirality of a biomolecule? A concentration gradient across a particular cell axis breaks symmetry in one direction. Add a couple more concentration gradients along different axes and it seems reasonable that a chiral structure could arise from signalling alone. The structures themselves may not have to be chiral if the rules for the signalling are "chiral".

Interestingly, the following paper finds left-handed chirality developing despite no chirality existing after the third division (which they determine to be the critical determinant of subsequent shell chirality). A chiral formation of cells after the third division yields right handed snails.

https://academic.oup.com/icb/article/54/4/677/2797866

They make a pretty fairly solid case for chirality arising from the chirality of biomolecules. In my eyes, they still fall a bit short of proving it though and they seem careful to phrase their results as such.

No, I can’t see a mechanism for chirality to simply arise.

A concentration gradient across a longitudinal axis with a head and a foot end would certainly do the trick, but how would that arise in the first place? Why would the gradient not equally arise in the opposite orientation? The gradient itself, combined with the axis, is chiral.

What drives the whole contraption to take on a particular chirality, and not the mirror image ? I would contend that if you trace it back all the way to the molecular level, it is being driven by chirality of some molecule.

 

[Scott Weinrich]

No, I can’t see a mechanism for chirality to simply arise.

A concentration gradient across a longitudinal axis with a head and a foot end would certainly do the trick, but how would that arise in the first place? Why would the gradient not equally arise in the opposite orientation? The gradient itself, combined with the axis, is chiral.

What drives the whole contraption to take on a particular chirality, and not the mirror image ? I would contend that if you trace it back all the way to the molecular level, it is being driven by chirality of some molecule.

Below is a thought experiment on spontaneous chirality

Suppose we have a cell with a membrane-bound protein that has some affinity for self association that causes one side to have more of the protein than the other (nothing inherently chiral). Now let's suppose that there is a correlation between this membrane protein and the axis of division such that there ends up being the pictured configuration that breaks symmetry:

Directional_division

• Scott Weinrich
• May 11, 2018

Now, let's suppose that a particular cell spontaneously starts producing species A. Adjecent cells experiential the gradient along different axes relative to the directionally of the membrane bound protein. Depending on the alignment of the adjacent cells relative to the gradient, one starts producing species B and one starts producing species C:

Spontaneous_chirality

• Scott Weinrich
• May 11, 2018

Would this not result in chirality? (Imagine tetrahedral geometry rather than the planar geometry). I'm not suggesting this is how snails work, but just trying to establish how chirality might spontaneously arise without any "seed" chirality.

 

[Randy Holmes-Farley Verified Community Expert]

Great thought experiment.

I think the picture on the far right bottom with 4 colors in it is not chiral as drawn planar. It superimposes on its mirror image. This effect is easiest to imagine if the mirror is in the plane of the screen, but below it: the image and the original superimpose. It had to try it with my wife's hand mirror and a drawing that showed through the back of the paper to be sure, but it does. The image in the mirror looks identical to the drawing.

That result might even be a rule for single plane arrangements of anything: it can never be chiral for this exact reason.

I'm having an issue with the stage of "(Imagine tetrahedral geometry rather than the planar geometry"), but I think you create both of the enantiomers equally (which is what happens molecularly too when a "chiral" molecule is made from achiral reactants, that is very common).

Here's my thought "conversion" to tetrahedral.

In the bottom right hand picture, the blue one is not shown touching A. But in a tetrahedral arrangement it would, but does it move to touch A by moving out of the plane of the board (one enantiomer), or into the plane of the board (the other enantiomer).

 

[Randy Holmes-Farley Verified Community Expert]

Well, the science geeks should really like this thread now.

 

[Randy Holmes-Farley Verified Community Expert]

No, I can’t see a mechanism for chirality to simply arise.

A concentration gradient across a longitudinal axis with a head and a foot end would certainly do the trick, but how would that arise in the first place? Why would the gradient not equally arise in the opposite orientation? The gradient itself, combined with the axis, is chiral.
.

I think I got that last statement wrong, actually. A gradient across a longitudnal axis, even with a pre-defined head and food end, is not, itself, chiral. Just rotating it about its axis makes the gradient point in the opposite direction, so it isn't chiral.

 

[Scott Weinrich]

Great thought experiment.

I think the picture on the far right bottom with 4 colors in it is not chiral as drawn planar. It superimposes on its mirror image. This effect is easiest to imagine if the mirror is in the plane of the screen, but below it: the image and the original superimpose. It had to try it with my wife's hand mirror and a drawing that showed through the back of the paper to be sure, but it does. The image in the mirror looks identical to the drawing.

That result might even be a rule for single plane arrangements of anything: it can never be chiral for this exact reason.

I'm having an issue with the stage of "(Imagine tetrahedral geometry rather than the planar geometry"), but I think you create both of the enantiomers equally (which is what happens molecularly too when a "chiral" molecule is made from achiral reactants, that is very common).

Here's my thought "conversion" to tetrahedral.

In the bottom right hand picture, the blue one is not shown touching A. But in a tetrahedral arrangement it would, but does it move to touch A by moving out of the plane of the board (one enantiomer), or into the plane of the board (the other enantiomer).

As pictured, I think it is still chiral in 2D space, i.e. omitting mirroring in the plane of the screen. Presumabley, the "tetrahedrafication" would require the initial 4 cell group to break symmetry along 2 distinct axes. The concentration gradient could then break symmetry along a third axis allowing for the development of chirality.

I'm totally a nerd about stuff like this.

 

[Randy Holmes-Farley Verified Community Expert]

As pictured, I think it is still chiral in 2D space, i.e. omitting mirroring in the plane of the screen. Presumabley, the "tetrahedrafication" would require the initial 4 cell group to break symmetry along 2 distinct axes. The concentration gradient could then break symmetry along a third axis allowing for the development of chirality.

I'm totally a nerd about stuff like this.

How could the location of the mirror impact whether something is chiral?