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Cryo-electron microscopy breaks a key barrier

nature.com

21–30 of 110 posts

Re: Cryo-electron microscopy breaks a key barrier

#21
post #9

So, pardon my ignorance, but can we finally say that atoms are particles with concrete dimensions? Last time I checked the whole field seemed measuring everything into probabilistic and statistical terms.

We can meaningfully talk about concrete dimensions just like before. Atomic radius is mean distance from the nucleus to the boundary of the surrounding shells of electrons.

Because the outer shell of electrons is fuzzy, there are multiple ways to define radius: covalent radius, Van der Waals radius and ionic radius. In molecules atoms overlap in different ways because they share electrons and electrons interact.

There still exists fundamental uncertainty about the location of atoms and molecules. Electrons, atoms and molecules have de Broglie wavelength. For molecules with tens of atoms the wavelength is in the order of picometers.

Re: Cryo-electron microscopy breaks a key barrier

#22
post #9

So, pardon my ignorance, but can we finally say that atoms are particles with concrete dimensions? Last time I checked the whole field seemed measuring everything into probabilistic and statistical terms.

Our understanding on the nature of atoms is not something someone suddenly "discovered". Rather, we've gathered evidence of various phenomena over the century. There are lots of models to explain the findings.

This is a bit of a long winded list of discoveries. There is no simple sophism you can utilize and say "atoms are this or that" unless you actually understand something of the background.

This Khan academy lecture is as good resource as any:

https://www.khanacademy.org/science/chemistry/electronic-str...

Re: Cryo-electron microscopy breaks a key barrier

#24
post #9

So, pardon my ignorance, but can we finally say that atoms are particles with concrete dimensions? Last time I checked the whole field seemed measuring everything into probabilistic and statistical terms.

You can resolve atoms despite all the uncertainty just like you can resolve a tree at distance despite it not having a clear surface.

The electron distribution falls with an exponential function on large distances, what is much cleaner than a tree surface anyway.

Re: Cryo-electron microscopy breaks a key barrier

#25

I'm curious could you use AFM/STM to image molecules? I'm curious how that would compare with this approach.

You can, and it has been done. But that was with very small, flat molecules. Cryo EM can be used with very large molecules or complexes with many tens of thousands of atoms.

Feels like this might be useful for exploring the surface of cancer cells to identify receptors and other features that might be useful for developing targeted therapies.

Re: Cryo-electron microscopy breaks a key barrier

#26

Earlier quoted context omitted.

We don't know yet. That is the idea about research. When the microscope was invented, people made the same question: What is the use of it? Just watching things we already know bigger? That is a recurring question. So much that Aristotle created the book MetaPhysics(meta meaning different from the Physics book) with the idea that this particular book did not need to be useful to be created. It was a compilation of no…

Oh please, this philosophical stuff is unnecessary. Cyro-EM is about a decade old and is just an alternative to X-Ray Crystallography for elucidating the structures of proteins. This article describes a way to improve the resolution of Cyro-EM, matching it to X-Ray Crystallography. The biggest bottleneck of X-Ray Crystallography is the production of protein crystals which is not necessary with Cyro-EM.

It's unbelievable how cryo-EM has come on. When i was a student, it was an also-ran behind crystallography and NMR, something that a few weird groups used to study a few special cases. Now you have to wonder if there's any point doing crystallography at all!

I still like NMR, because you're looking at proteins in solution. But if the freezing is good in cryo-EM, maybe even that becomes moot.

Re: Cryo-electron microscopy breaks a key barrier

#28

Dumb question, but if electrons are basically point particles, why is hard to get below 1 angstrom resolution?

At these scales, electrons behave more like waves than particles. Also the way that they are scattered by the subject and manipulated via em lenses causes information loss.

Re: Cryo-electron microscopy breaks a key barrier

#30
post #13

Earlier quoted context omitted.

Not an expert, but as far as I understand it, both, i.e. atoms are ("physical") manifestations of (probabilistic) quantum fluctuations. If I'm wrong, it would be great if someone could ELI5.

I hope somebody weighs in because ever since I read that matter is just quantum field excitations I've lost all intuition about what reality is. Everything seems to be nothing.

Learn about the quantum eraser experiments and your jaw will drop.

https://youtu.be/8ORLN_KwAgs

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