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Are there known life forms that are able to transform mechanical energy into chemical energy?

This question asks a similar subject, but more specific and has no answers.

The background of this question are thoughts about hypothetical life on tidally locked exoplanets of red dwarf stars, where light for photosynthesis is scarce but mechanical energy (storms and/or water currents) aplenty.

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There are no known life forms that use mechanical energy as a primary form of metabolic energy (i.e., for generic cellular functions). Many life forms are sensitive to mechanical disruption in some way, so they do utilize mechanical energy, but in a very limited fashion (@David's answer touches on this), and of course many organisms have life cycles that somehow depend on mechanical transportation (seed/spore dispersal, traveling on the wind or ocean currents, etc).

I think the main physical problem is that mechanical energy just isn't available to biological cells in a form that can be converted to substantial chemical energy. They are small, and tend to have other great benefits for being small.

To use an ocean wave as an example, there is very little or no perceptible movement for a cell in that wave, besides an apparent increase and decrease in the force of gravity. The top and bottom of the cell are moving together with the flow of water, so there is no differential to operate on.

An E. coli weighs about 1 picogram. If it could capture all of the energy from falling from 1km in the air on earth, assuming no uncaptured aerodynamic drag, that would be about 10-11 joules.

If there are ~3000 kJ/mol of energy available from burning glucose, that means about 5 × 10-21 joules per molecule of glucose, so about 20 billion glucose molecules, which sounds like a lot but it is only 1 femtogram, 0.1% the weight of the cell.

Also note: in @David's answer he makes a very good point that in a way, using mechanical force to open a channel is indeed a form of energy usage and therefore a proof of concept that this could happen. To put that process in the same ballpark, this source (originally mentioned by @GerardoFurtado) gives the work necessary to open one of these channels at around 8 × 10-22 joules. The open latency for those channels is under 50 microseconds, but that still greatly limits the number of possible cycles per unit time. Chemical energy is just substantially more dense than mechanical energy is: that's why gunpowder superceded catapults (and even the trebuchet..).

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  • $\begingroup$ Not an answer to the question, but a very useful consideration. $\endgroup$ – Gyro Gearloose Jul 12 '17 at 18:17
  • $\begingroup$ @GyroGearloose I'll add an answer to it, I guess I left it out a bit. $\endgroup$ – Bryan Krause Jul 12 '17 at 18:18
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    $\begingroup$ @BryanKause no hurries and no worries. Your consideration is appreciated. $\endgroup$ – Gyro Gearloose Jul 12 '17 at 18:24
  • $\begingroup$ 'Open latency' do you mean the duration of the channel remaining open? $\endgroup$ – Mockingbird Jul 13 '17 at 9:54
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    $\begingroup$ @Mockingbird The time from deflection of the tip links to when the channel is able to pass ions. $\endgroup$ – Bryan Krause Jul 13 '17 at 14:45
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This is definitely not my field, and I have no interest in science fiction, but the question struck me as interesting, and brought me to an area of bimolecular science that may be relevant to the question.

First, in direct answer to the question, I do not know of any examples of life forms of the type you suggest.

However there are examples of biological processes involving mechanical movement resulting in the ‘release’ of electrical energy. The following recent paper drew this to my attention, and the introduction contains background reference to the phenomenon.

Electron cryo-microscopy structure of the mechanotransduction channel NOMPC.

It turns out (thank you @Bryan_Krause) that the electric current is the result of the opening of a ‘gate’ to dissipate a pre-existing ionic concentration gradient, established beforehand by the expenditure of cellular chemical energy in the form of ATP. Nevertheless, the opening of these gates must involve an effect on the conformation of the protein or protein complex involved in maintaining the gate, and can be regarded as the harnessing of mechanical energy to drive the complex from a conformation state of lower to one of higher free energy.

The amount of energy involved in this case may be quite low — a few hydrogen bonds compared to the order of magnitude higher energy of hydrolysis of ATP. However it is an interesting ‘proof of principle’. If minute amounts of mechanical energy can be transformed in this way, I wouldn’t bet against organisms being found in some niche that harvested more energy and used it to greater effect. As a primary source of energy for life? Perhaps not.

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  • $\begingroup$ This is, indeed, really nice. However, that kind of receptor is not new, have a look at this image from Alberts, 15 years ago: ncbi.nlm.nih.gov/books/NBK26868/figure/A4107/?report=objectonly. Besides that, this is just a gate: It doesn't convert mechanical energy into chemical energy, it only allows the exchange of Na+/K+, as any other gate. $\endgroup$ – user24284 Jul 12 '17 at 13:47
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    $\begingroup$ To add to what @GerardoFurtado wrote there are also receptors for mechanotransduction in several sensory systems: all the different forms of touch, proprioceptive sensation in your muscles and tendons, auditory and vestibular systems, etc, and there are also cells that are somewhat more accidentally mechanotransducive (for example, if you press on the side your eye, you "see" things in the visual field corresponding to that part of the retina - please be careful). They all have in common that they utilize preexisting concentration gradients. $\endgroup$ – Bryan Krause Jul 12 '17 at 15:40
  • $\begingroup$ @BryanKrause — Thanks. I was wondering about that very point. Before I edit or delete my answer, can you tell me whether I would be correct in thinking that the mechanical energy is used to convert a protein (or protein complex) from a lower free energy structure (which maintains the gate closed) to a higher free energy structure in which the gate is (temporarily) open? $\endgroup$ – David Jul 12 '17 at 16:21
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    $\begingroup$ I'm afraid that the mechanism only triggers the conversion of previously available chemical energy to electric energy, like a button on an electric torch triggers the conversion of chemical energy in the battery to electrical energy used by the lamp. No energy added from mechanical sources. The mechanism looks worth mentioning, though. $\endgroup$ – Gyro Gearloose Jul 12 '17 at 18:21
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    $\begingroup$ @Mockingbird — Thank you for your interest in my answer and Bryan Krause’s comment. The correct procedure for agreeing with a comment is to upvote it (assuming you have that privliedge). As with answers, it is not the purpose of comments to write "me too", with no explanation, as that is not helpful to the answerer (me in this case) or other readers. I would remind you that the question was not about finding analogies to describe biological mechanico-transduction processes but about their energetics. My answer attempts to address this by considering the free energy changes in the system. $\endgroup$ – David Jul 13 '17 at 10:57
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I did read and article about some bacterial spores being used to generate electricity as they expand and contract. Not sure if that is a relevant answer but that's what came to mind when I read your question. https://www.sciencedaily.com/releases/2014/01/140127101242.htm

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    $\begingroup$ Regrettably, I can't open that link. It gives me "Error code: ssl_error_no_cypher_overlap". I've heard about such experiments, but what I know is that those organisms are only used to produce cheap micro-structures en mass. They are dead when the experiment starts. Nothing to do with biology. Maybe your link points to something different, but I can't verify it. $\endgroup$ – Gyro Gearloose Jul 12 '17 at 18:16
  • $\begingroup$ @GyroGearloose Yeah that's basically the gist of it: when the whole sheet dries out, it shrinks, so if it's fixed to a flexible material, that material bends. A biomaterial, in a way, but the transduction is not biological at all. $\endgroup$ – Bryan Krause Jul 12 '17 at 23:22
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No, as the mechanical energy cannot be harvested at the lenght scale cellular life exists at. Cellular life exist at a length scale were viscosity is the primary force at work, a force which must be overcome by expending energy.

There is a nice article here that details what can be done with mechanis by small organisms/cells: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4451180/

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  • $\begingroup$ The source you quote is a top journal, and the point you make may be valid, but an answer here must be comprehensible in itself — we can't be expected to go and read a paper to understand the answer. So please edit your answer to explain why "mechanical energy cannot be harvested at the length scale cellular life exists at." and what viscosity has to do with this. I appreciate this is a chore if English is not your first language, but it could make your answer much more useful to us all. $\endgroup$ – David Jul 15 '17 at 10:45
  • $\begingroup$ If you all want me to fine, but it will take quite a bit of physics to explain. I decided to give the shortest and most precise answer which wouldn't require an university degree to understand. $\endgroup$ – Jeppe Nielsen Jul 16 '17 at 22:38
  • $\begingroup$ Simple realise that life exist at the micrometer scale and that the molecular machinery necessary to harvest mechanical energy would have to exist at the nanometer scale. At such small scale the individual interactions of atoms are much stronger than the mechanical energies applied. For instance cells can tolerate a couple of thousand g, while biomolecules such as proteins can survive several tens of thousands g. While mechanical influence can be sensed, it cannot be used to maintain ion gradients across membranes and therefore cannot drive ATP synthesis. $\endgroup$ – Jeppe Nielsen Jul 16 '17 at 22:54

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