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goltz20707 t1_isfqew0 wrote

All bacteria and protists with flagella propel themselves by spinning the end, not wriggling. They use proton-powered rotary motors.

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SaintUlvemann t1_isgnvv3 wrote

Eukaryotic flagella aren't helical, though. There are multiple types of flagella. Description:

>Bacterial flagella are helical filaments, each with a rotary motor at its base which can turn clockwise or counterclockwise. ... > >Archaeal flagella (archaella) are superficially similar to bacterial flagella in that it also has a rotary motor, but are different in many details and considered non-homologous. > >Eukaryotic flagella — those of animal, plant, and protist cells — are complex cellular projections that lash back and forth. Eukaryotic flagella and motile cilia are identical in structure, but have different lengths, waveforms, and functions.

...and diagram.

That's why the rotary motion is a surprise.

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LostFerret t1_isgypue wrote

Rotary motion is not a surprise. See paper from 1901 https://www.jstor.org/stable/pdf/2453750.pdf

More work building on this with self powered nanomachines https://journals.aps.org/rmp/pdf/10.1103/RevModPhys.88.045006

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SaintUlvemann t1_ish61aq wrote

Right, but assuming you are referring to page 370 of the first link, this is the reason they gave for this spiral motion:

"The Flagellata and Ciliata are as a rule asymmetrical in form. One of these organisms, as, for example, Loxodes (Fig. 2), or Paramecium (Fig. 3), when it leaves the bottom and starts to swim freely through the water, cannot go in a straight line, but owing to its lack of symmetry continually swerves toward one side, so that it tends to describe a circle."

This is not a disputation of how the cilia or flagella beat, but rather a description of the effect such beating has on an asymmetrical object. This does not apply to sperm cells since, in terms of their form, they *are* symmetric in shape, apart from the shape deformations caused by the flailing of their flagellum itself.

In contrast, the paper we're talking about purports to have found that sperm cells fundamentally do not even beat back and forth in the first place; they only beat in one direction, and then they continuously rotate the mass of the entire "head" of the sperm, in order to keep themselves moving forward.

That's different than what your paper shows.

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LostFerret t1_ishybgl wrote

Ah, sorry, didn't realize that second paper was paywalled. Fhe first paper focuses on form generating asmety in cilliated swimmers, the second paper extends that to asymmetry in either form or force and classifies swimmers as pushing (posterior flagellum) or pulling (anterior flagellum).

Both papers present the idea that any asymmetry in the swimmingof unicellular swimmers will produce circular or irregular patterns unless balanced by regular rotation linked to those forces. This is further explored in that more recent paper.

We expect EVERY eukaryotic, unicellular swimmer capable of helical / straight lines to follow this behavior, its just the way that the physics of swimming work at low reynolds numbers. Honestly, it would be way more surprising if we found a unicellular swimmer that did NOT spin while swimming.

So while sperm bodies may be somewhat symmetrical (im not sure if this is actually the case? There are a ton of weird fuckin sperm out there..google ostracod sperm for a trip..i dont know the range of human sperm morphology), the force they are producing is definitely not. To counter this asymmetry they rotate the entire cell, not just the head. This creates a helical procession that lets the sperm swim relatively straight.

We've known that euk. Flagellum don't beat in a single plane for a while, so im surprised we hadn't picked up on the asymmetrical beat pattern of human sperm until now. The imaging is pretty cool here though, I'd love to get my cells on that scope though they're tiny compared to sperm.

The title of this post is hot garbage tho, i was so happy to see you post about the prot/euk flagellar difference.

I think this is just a case of silo'd science. I only found those two papers because im working with weird non-animal cells and the modelers im collaborating with had some questions we couldnt answer so i did a very thorough literature search. They do bacterial motility modeling and hadn't seen the paper despite it being directly related to one of their theses. Human research, especially sperm research, is pretty isolated so it's likely the researchers who published the new paper didnt know it exists.

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schizboi t1_isj3d7p wrote

Love the sources, doing the lords work here thank you

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SaintUlvemann t1_isjfsoh wrote

Ah, thanks for that: that second one was paywalled, yeah, and ostensibly my institution doesn't have a subscription. I'd even written something saying so, but, I lost it 'cause of whatever bug it is leads comment text to go missing after copypaste, was too lazy to rewrite.

>I think this is just a case of silo'd science.

Yeah... I'm pretty sure a pretty core chunk of my thesis is essentially just a case of me speaking into the silence of missing knowledge, created by siloed science... a siloed science silence, if that ain't too pretentious.

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on_ t1_isgj777 wrote

That’s pretty amazing cause nature doesn’t like to evolve in rotary thingys. I think in macro world there’s only one insect specie that has a rotary mechanism? Our lives would be better if we as humans had segway wheels instead of legs.

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goltz20707 t1_isgjupk wrote

Protista “motors” are constructed at the molecular level, with (in the case of human sperm) 16 proteins in a ring. One proton per protein rotates the ring by one protein, so 256 protons are required per rotation. Scaling that up to the macroscopic level, even just to the size of a small insect, would require a very complex design. I can’t see such a design evolving naturally — it would take deliberate “intelligent design”.

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bubliksmaz t1_ish4a8y wrote

It's not the complexity that precludes certain things evolving - organisms are fucking complex enough. It's the fact that evolution needs to happen in tiny incremental steps, each of which are beneficial to the organism. For legs, that's easy: First they're just fins for swimming, then maybe they're used to drag ones body across a short stretch of very shallow water, then they gradually take more of the weight to make locomotion more efficient. For a wheel and axle... nah.

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goltz20707 t1_ishbsqj wrote

I guess what I meant is that a protein-proton motor that uses things like van del Waals forces and molecular mechanical mechanisms to create motion cannot work at the visible scale. I agree that complexity is no barrier for evolution—look at clotting factor chemistry—but I can’t imagine an incremental path to “wheels”. (I will admit it may be possible.)

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nsaisspying t1_isiyuq1 wrote

Have you read the book Climbing Mount Improbable?

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kommandeclean t1_islbffo wrote

Sort like humankind's intelligence, it will require some "intelligent design" to bestow upon us intelligence inside an organ .. psstt.. you are right crazy to think that.

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goltz20707 t1_isligjz wrote

If you can convince me that you even come close to understanding proton-pump biology and why that cannot, cannot possibly scale past the molecular level, I’ll consider your argument.

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kommandeclean t1_ism1l7u wrote

Your crude attempt to humiliate me tells me that maybe your brain is an example of failed scalability of intelligence in neural networks.

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goltz20707 t1_ism3fpr wrote

I apologize. I should know better than to escalate an argument like this. If it’s put you into a depressive spiral like it has me, then I doubly apologize. Antagonism was not my intent.

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dogfish83 t1_ishw888 wrote

I’ve been watching modern videos on molecular biology and it’s way better than when I was in HS, so I am really into this right now. And the rotary concept has been my primary thought. How hard would it be to make artificial molecular rotary motors I wonder…

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Antares30 t1_ish0rwn wrote

Intergalactic proton-powered electrical tentacled advertising droids!

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V6Ga t1_ishyhba wrote

I tried to sing this to the Beastie Boys song, but could not make it work.

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VerumJerum t1_ishabl3 wrote

It makes sense, considering how relatively viscous fluids are on that scale. Even water is like honey to bacteria.

Besides, we humans ourselves have shown how effective propellers are.

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