Are cones in eyes sized to the light's wavelengths they perceive?

[syfry]

TL;DR

Are the 3 types of cones sized differently to interact with the wavelength of light they're for?

Each of the 3 primary colors have a different wavelength so I'm wondering if that means each type of cone has a different size than another type.

 

[BillTre]

No, the specificity of color of light received by the sensor is due to the different forms of rhodopsin molecules expressed in the different cells.

 

[syfry]

different forms of rhodopsin molecules

That's even more interesting.Are the molecules differently sized in any way that suggests a pattern with the wavelength they sense, if you happen to know?

 

[BillTre]

Here, read this:
https://en.wikipedia.org/wiki/Opsin

Your questions reveal that you should learn some basic biology.

 

[syfry]

Here, read this:
https://en.wikipedia.org/wiki/Opsin

Your questions reveal that you should learn some basic biology.

Thanks for linking that. Didn't know those even existed.

The article doesn't mention size of the molecules and I suspect that only a lab person who directly studies them would know the answer. But that's still a useful insight to be aware of. I'm sure some of the lab people have times when they seek additional income, and they might be open to a funding model where curious people collaboratively pay good money for answers they know are reliable: being directly from the source, from the explorers.

There's potential since Wikipedia and textbooks cannot clarify nor address the follow up questions people often have. It's unlikely the majority of everyday people can afford to satisfy their curiosity individually by pursuing a route of knowledge with many prerequisite courses without knowing if the answer they're seeking even exists in the articles and textbooks.

I mostly wrote what came to mind in the above, after wading through the Wikipedia article, more to express my thoughts than as a direct reply.

But thanks again for the link. Learned that the opsins can cover more senses than only vision. Really cool!

 

[BillTre]

If you have follow up questions, it is not very difficult to follow up with additional searches based on your new questions. No one is going to be able to anticipate all of anyone's questions, but you can certainly easily do follow up searches based on your further questions.

 

[syfry]

If you have follow up questions, it is not very difficult to follow up with additional searches based on your new questions. No one is going to be able to anticipate all of anyone's questions, but you can certainly easily do follow up searches based on your further questions.

True. I had meant when searches don't turn up anything, then it's possible that people in labs who are exploring the frontiers might know something that a student wouldn't have learned, or, they might be able to check.

A good funding model for that might be a potential source of extra income for them.

Anyway, did a search and found unrelated info that revealed I had underestimated the amount of cones in the eye. (hyper physics a great source)

And digging deeper, the info helps me to form an educated guess that such an answer might be at the edge of science or currently inconclusive / unreachable:

By population, about 64% of the cones are red-sensitive, about 32% green sensitive, and about 2% are blue sensitive. The "blue" cones have the highest sensitivity and are mostly found outside the fovea. The shapes of the curves are obtained by measurement of the absorption by the cones, but the relative heights for the three types are set equal for lack of detailed data. There are fewer blue cones, but the blue sensitivity is comparable to the others, so there must be some boosting mechanism. In the final visual perception, the three types seem to be comparable, but the detailed process of achieving this is not known.

When light strikes a cone, it interacts with a visual pigment which consists of a protein called opsin and a small molecule called a chromophore which in humans is a derivative of vitamin A. Three different kinds of opsins respond to short, medium and long wavelengths of light and lead to the three response curves shown above.

(emphasis mine)

Based on that tidbit, I'm thinking there's an explanation for why each type has a different response to the wavelengths of light that activates them. My best educated guess is that size might be one of the explanations, but didn't find anything to confirm in a search.

The snippet below seems to be saying an interaction between the proteins and chromophore enables the activation by wavelength, but I might need to know more about physics to understand what they're really saying:

Besides several structural and functional similarities between Rh and cone opsins, including (i) heptahelical transmembrane architecture, (ii) an ultrafast photoinduced cis-trans isomerization of the chromophore, and (iii) signal transduction through the interaction with heterotrimeric G protein, cone opsins exhibit a relatively faster activation, inactivation, and regeneration than Rh (2, 3). These differences are attributed to the specific interactions between 11-cis-retinal and the chromophore-binding pocket of each pigment. The distinct chromophore–protein interactions also determine the light absorption properties of these receptors (4).

On the molecular level, Rh has been extensively studied by X-ray crystallography (5–9), NMR (10 –12), FTIR (13–15), and resonance Raman spectroscopic techniques (16, 17). These structural studies determined that the chromophore-binding pocket of Rh largely comprises hydrophobic residues that enable accommodation of the retinal chromophore molecule and dictate its photochemistry

(emphasis mine)

But even without finding a specific answer, your reply helped guide my search to be better than my previous one. Sometimes a person needs a springboard that a more knowledgeable person can provide.

 

[DaveC426913]

There is almost certainly no physical correlation between the wavelength of light and the physical size of the molecular bonds. That's not how photochemical reactions work.

For one, wavelength is not the relevant property of light that molecules respond to. The relevant property is frequency, which is correlated to the specific quantum of energy that the bond can absorb.

 

[snorkack]

There is almost certainly no physical correlation between the wavelength of light and the physical size of the molecular bonds. That's not how photochemical reactions work.

There is a correlation, but...

For one, wavelength is not the relevant property of light that molecules respond to. The relevant property is frequency, which is correlated to the specific quantum of energy that the bond can absorb.

But that correlation is not equality. Hydrogen atom has radius of 53 pm. It is ionized by light with wavelength 91 200 pm and excited by light with wavelength 121 600 pm. Neither of which is a small multiple of the size of hydrogen atom.
As pointed out, atoms and molecules match frequency not wavelength, and electrons are much slower than light.

Now, the various opsins are typically retinal - vitamin A - bonded to some type of opsin protein.
Retinal is a conjugated chain of 6 double bonds. 1 of them in the cycle, then 4 C=C double bonds in the side chain and the C=O double bond of aldehyde.

Yes - if you replaced vitamin A with a conjugated chain having 5 or 7 double bonds, you would change the spectral sensitivity. But this is not what eye does.

When you blow a pipe, the wavelength of the tune is four times the length of the pipe, and you can tune it by changing the length.
When you pluck a string, yes, its tune is related to its wavelength, in that a longer string tends to have a longer wavelength tune. But unlike pipe, there is no small integer relationship between length of string and its tune - nor indeed one to one relationship. You can tune a string by changing its length, but you can also tune a string by adjusting its tension, which changes wavelength without changing length.

The difference between various colour opsins seems to be change in the amino acids away from the retinal. Not changing the overall size of the opsin much... but apparently changing the mechanical environment of the retinal. And with that, the frequencies to which it is sensitive.
Can anyone add details?

 

[syfry]

Good to see more info on particulars at the cellular and molecular levels!

What I don't get is how frequency vs wavelength would matter, since they're inversely related.

Is it that they'd matter as some part of an equation or in a specific mathematical formula?

If a certain frequency of light has an effect, then so does a certain wavelength, right? For example, physically, light with a higher frequency can harm biology, and similarly so can light of a shorter wavelength.

 

[DaveC426913]

If a certain frequency of light has an effect, then so does a certain wavelength, right?

Yes. They are reciprocally correlated. Wavelength x frequency = a constant.

What I don't get is how frequency vs wavelength would matter, since they're inversely related.

I have been taking your initial questions at face-value. You seemed to be groping for an explanation of the colour receptors that involved a direct correlation between a wavelength of light and the length of a molecule or molecular bond it might affect - as if somehow the crest-to-crest length of a cycle would have to fit into the molecule's bnd length - or something.

If you are abandoning that idea (or if I was taking it too literally), and are simply asking if the frequency of light has a discrete effect on different molecules ... then, yes.

If a certain frequency of light has an effect, then so does a certain wavelength, right? For example, physically, light with a higher frequency can harm biology, and similarly so can light of a shorter wavelength.

Yes because they are simply two ways of describing the same thing.

Radiation with a wavelength of 220nm is the same as 1,362,692,990MHz - UVC light.

 

[syfry]

Oh ok. I was thinking along the lines of how only a specific wavelength of light can interact with a bound electron or it'll instead bypass the electron without interacting.

Had tought maybe something similar with the cones is the mechanism for their activation.

 

[hutchphd]

Thanks for linking that. Didn't know those even existed.

Here is another good link

Yes because they are simply two ways of describing the same thing.

Yes but......the wavelength directly gives the quantized momentum and the freqency gives the energy. Yes they are related but we are talking about scattering here, and each must be separately conserved by the scattering. One often plots the dispersion curve s ($\omega ~vs. ~\vec k$) to look for possible scattering partners.

 

[snorkack]

Another thing: when light passes into a medium (and eyes are in a medium), its wavelength changes but frequency does not. And as I pointed out - the electrons resonate with light because although the electrons are much slower than light (even in the eye), the frequency matches.

 

[DaveC426913]

Oh ok. I was thinking along the lines of how only a specific wavelength of light can interact with a bound electron or it'll instead bypass the electron without interacting.

That is correct. It's really just a nitpicking that it's more concerned with the frequency - the energy - rather than the wavelength - the physical distance between crests.