Bacterial flagellum

Yes. It does rotate in its socket; no question. The rapid rotation of a long thread like object does cause it to whip about, especially in such small structures. The whipping effect induced by the rotation is what allows it to propell the bacterium.Cheers -- Sylas

A look at some relevant literature will show that the prevailing view certainly is that the hook is rotated by associated proteins in the basal body.

quote:

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Flagellar movement driven by proton translocation.
Blair DF.
FEBS Lett. 2003 Jun 12;545(1):86-95.

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The bacterial flagellar motor couples ion flow to rotary motion at high speed and with apparently fixed stoichiometry. The functional properties of the motor are quite well understood, but its molecular mechanism remains unknown. Recent studies of motor physiology, coupled with mutational and biochemical studies of the components, put significant constraints on the mechanism. Rotation is probably driven by conformational changes in membrane-protein complexes that form the stator. These conformational changes occur as protons move on and off a critical Asp residue in the stator protein MotB, and the resulting forces are applied to the rotor protein FliG.

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One reference which I could only get the abstract for seems to suggest that the molecular mechanism is ratchet like, i.e the proton gradient drives a variety of conformational changes in the stator so the FliG or some such element connected to th MS ring is continuously in contact with some portion of the stator but moved in such a way, ratcheted, that it drives rotary motion of the flagella, which I would say is distinct from a freely rotating system. This mechanism would be similar to the cross-step mechanism in actin/myosin interactions.

quote:

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Philos Trans R Soc Lond B Biol Sci. 2000 Apr 29;355(1396):491-501.

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Constraints on models for the flagellar rotary motor.

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Berg HC.

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Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA
02138, USA. hberg@biosun.harvard.edu

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Most bacteria that swim are propelled by flagellar filaments, each driven at its
base by a rotary motor embedded in the cell wall and cytoplasmic membrane. A
motor is about 45 nm in diameter and made up of about 20 different kinds of
parts. It is assembled from the inside out. It is powered by a proton (or in
some species, a sodium-ion) flux. It steps at least 400 times per revolution. At
low speeds and high torques, about 1000 protons are required per revolution,
speed is proportional to protonmotive force, and torque varies little with
temperature or hydrogen isotope. At high speeds and low torques, torque
increases with temperature and is sensitive to hydrogen isotope. At room
temperature, torque varies remarkably little with speed from about -100 Hz (the
present limit of measurement) to about 200 Hz, and then it declines rapidly
reaching zero at about 300 Hz. These are facts that motor models should explain.
None of the existing models for the flagellar rotary motor completely do so.

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In this paper Berg describes a hypothetical cross-step mechanism.

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Given the work of Blair and colleagues, I favour a
cross-bridge mechanism of the kind envisaged by Luger
(model II of Luger (1988)). In this scheme, proton trans-port
drives a cyclic sequence in which (i) a proton binds
to an outward-facing binding site (presumably, Asp32 of
MotB), (ii) the protonmotive force drives a conforma-tional
change, a power stroke (Berry & Berg 1999) that
moves the rotor forward (or stretches a spring that moves
it forward) and transforms the binding site to an inward-facing
site, and (iii) proton dissociation triggers detach-ment
of the cross-bridge from the rotor, its relaxation to
the original shape, and reattachment to an adjacent site.
If step (iii) is relatively fast, the cross-bridge will remain
attached to the rotor most of the time.

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TTFN,WKP.S. My apologies if this is too extensive quoting.

So, what exactly propels it? What's the mechanism? Oh, wait, never mind, I read further in the thread.Moreover, why doesn't it just spin the bacterium? Or does it, and that's why it's not all that efficient?This message has been edited by crashfrog, 05-20-2004 01:52 PM

My understanding is that it does spin the bacterium. I don't know that I'd call the motor "inefficient", however.The way in which direction is apparently achieved is inefficient, however. (Though I'd say it is remarkable efficiency to pack an effective motion system into such a tiny package!)My understanding is that bacteria usually spin for a short time, moving in a mostly straight line at signficant speeds. Then they stop, and have a short "tumble". Then they move off again, in a different completely random direction.So how do they get direction? Interestingly, it is by a kind of analog to selection and variation! Suppose, for example, that a bacterium tends to move towards a light source. The way this is acheived is by having the length of time of the straight line movement be related to the light intensity. In a dark place, they tend to move in straight lines for a longer time before entering the tumble mode. This increases the probability that they will move away from the dark.Cheers -- Sylas

( Duplicate post bug; apparently caused when I refreshed the response screen which had failed to load properly. }This message has been edited by Sylas, 05-20-2004 05:41 PM

While a single flagellum may be inefficient they often occur in groups. A grouping of flagella can synchronise and act as a single large flagellum with considerably greater efficiency.Interestingly there is another rotatory proton pump system, ATP synthase. Here is a link to the relevant page in the online version of Stryer Biochemistry.TTFN,WK

Wild stuff. Well, never let it be said I won't admit it when I'm wrong - I was wrong about the bacterial flagellum. Clearly I misunderstood The World of the Cell; probably it was only referring to the eukaryotic flagellum.Neat stuff, though. I don't even begin to understand it, though.

Is that the same as gyroscopic effect? I never heard it put that way, it sounds cool.Wouldn't the fact that the tail can whip around into various shapes enable it to counter act the tumbling period of motion, without reversing? Juust a thought.

Hmm, then is the flagellum using ions, or electric pulses?

Thats due to the effecientcy of the tail, not the motor.
I was only speaking of the motor.

Yes both. Its the whipping spinning action.
If it just spun, how would it stear?

Woa!I'm not sure how to comment on this one, but I sense something wrong with that deduction.
You are saying that the bacterium is not intelligent, or is it intelligent.
Is it a fact that they can sense light?
Also we need to look at the function of these things within the bacteria. They do have a purpose other than just swimming to the light?

It's not too hard to concieve of a metabolic pathway in a bacterium that would supply more or less energy to the flagellum based on the intensity of light at another part of the bacterium. Light can catalyze chemical reactions.

I suggest that if you want to distinguish between the "motor" and the flagellum as a whole you make it clear.

Apologies if I get this a bit wrong, as it's a while since I covered this, and I'm doing this from memory and a quick look at Alberts et al. The way it works is something like this:The flagellum have a very dinstict 'handedness', and as may have been pointed out already can spin in both directions. This is what causes the run and tumble effect that Sylas has mentioned. When the flagellum turn in one direction then they all effectively work together and the E Coli (or whatever) 'runs' in one direction. Every few seconds the flagellum turn the other way and the cell 'tumbles' on the spot.Without the presence of stimulus then this is effectively random, but there are mechanisms that will 'sense' certain chemicals (and possibly sunlight, although I'll have to check that), and these will effect the direction of turn of flagellum and hence make the bacteria travel towards or away from stimulus.Hope this helpsEdit: overexcitable typingThis message has been edited by Ooook!, 05-21-2004 08:43 AM