Thought Provoker
Posts: 530
Joined: April 2007
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Hi qetzal,
You wrote...
| Quote | | So, what we really have is a series of reference showing that tubulin can adopt curved structures when it is not part of a microtubule. |
After doing some digging I have found that it is generally accepted that intact microtubules contain both configurations of tubulin. The Alpha tubulin monomer binds with GTP. The Beta tubulin monomer binds with either GTP or GDP. If Beta monomer binds with GDP the tubulin dimer is curved.
A microtubule with curved tubulin dimers on the end cap will start falling apart with the curved tubulins becoming loose. Therefore the end caps of intact microtubules have straight tubulin dimers. However, the middle section can, and does, contain curved dimers.
Here is a fairly easy to read paper from Mershin, Kolomenski, Schuessler and Nanopoulos titled...
Tubulin dipole moment, dielectric constant and quantum behavior: computer simulations, experimental results and suggestions.
It explains the GDP and GTP binding. The paper also includes this in its discussion section...
Regardless of whether it turns out that tubulin and MTs are purely classical systems or they have a quantum nature, the excitation and detection of the theory-suggested ’flip waves’ would be an important step towards understanding the role that tubulin and MTs can play as binary switches and networks respectively, both in naturally occurring systems such as living cells as well as in synthesized structures. Note that the energy needed for a tubulin conformational change or ’flip’ is roughly 200 times lower than a conventional silicon-based binary switch, making laser-pulse induced switching feasible. This conformational change energy is also about 30 times larger than thermal noise at room temperature, making the system reasonably resilient to thermal noise.
And its summary section...
Theoretical efforts by us and others have strongly suggested that tubulin is near the "front lines" of intracellular information manipulation and storage. Our group has performed preliminary measurements on tubulin in an effort to supply experimentally determined parameters (such as the refractive index, polarizability and dipole moment) to apply to the various models of tubulin.
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We used computer simulation to calculate the electric dipole moments of the two tubulin monomers and dimer and found those to be |p?|=552D, |p?|= 1193D and |p??|=1740D respectively. We used refractometry to corroborate our previous SPR-derived result (equation(1)) for ?n/?c ~1.800ml/mg. The refractive index of tubulin was found to be ntub ~2.90 (3) and that gives the high frequency tubulin dielectric constant at ?tub ~8.41 (4). In addition, the highfrequency polarizability was found to be ?tub ~ 2.1x 10-33 C m2/V(5). Several methods were described to determine the low-frequency DC-p as well as to check for both coherence and entanglement among tubulin dimer dipole states. An experiment was suggested whereby using a perforated metal chip layered with a network of aligned MTs, and employing entangled photons in the SPR-exciting laser beam, it can be determined whether surface plasmons interacting with MTs can stay entangled and whether this entanglement can be propagated and conserved by the biomolecules.
In its conclusion...
The electric and energy-transduction properties of tubulin and the polymers it forms are important not only because of the role these play in intracellular protein interactions but also because it may well be that nature has already provided us with suitable nanowires, switches or even logic gates. Beyond the obvious benefit to the credibility or otherwise of the various "quantum brain models", determining the dipole moment of tubulin and its dynamics will further our understanding of tubulin and other similar proteins (such as actin) and will shed light on whether we can use these as the basis of biomolecular electronic circuits of even quantum information processing.
Tubulin, microtubules and the dynamic cytoskeleton are fascinating systems and in their structure and function contain the clues on how to imitate nature in artificially fabricated biomolecular information processing devices paving the way for biobits and perhaps even bioqubits.
While this paper presented a specific positive picture of the Orch OR model, it is just one of many talking about the different types of tubulin dimers that make up microtubules. Early papers talked about one type for the ends and the other type for the middle, but it was clear it is generally assumed both types are present in an intact microtubule.
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