|
|
Microtubules and coherent excitations
A
critical assessment of the information processing capabilities of neuronal
microtubules using coherent excitations
Travis J. Craddock & Jack A.
Tuszynski, University of Alberta
Journal
of Biological Physics, January 2010, 36(1) pp. 53-70
http://springerlink.com/content/102921/
The authors stress that
microtubules (MTs) appear likely to be involved with numerous functions in
neurons such as ion channel activity, enzyme catalysis, and the movement of
motor proteins. The degeneration of MTs is also related to Alzheimers. Studies
have shown a double well structure within the tubulin dimer, and there is the
potential for an electron to undergo transfer within the protein. If the
electron is in a superposition between the two wells if the tubulin is to act
as a qbit. The authors, however, take the view that electrons in the double
well would be vulnerable to decoherence. The authors point to the possibility
that coherence within microtubules could be shielded by various factors, but
they admit that to date there is no experimental evidence for such mechanisms.
Instead, the authors examine role of the amino acid, tryptophan, within the
tubulin dimers. Studies of tryptophan suggesting that electron transfer involving
tryptophan may have a role in protein function. A study by Becker et al has
demonstrated photon exchange between tryptophan and aromatic molecules in
adjacent tubulins, which suggests that tryptophan has a large electron
resonance, and is therefore suitable for transferring electrons and exchanging
photons within microtubules.
Polarising London forces, a form of attraction
between dipoles, very much weaker than covalent bonds, may influence electronic
transitions within the double well, so that the double well amplifies the
quantum effects of tryptophan's aromatic rings. This proposed mechanism is not
looked at in detail in this paper. However, it is pointed out that structures
not dissimilar to aromatic rings support room temperature quantum coherence in graphene
and conjugated polymers. Perhaps more significantly, the structures that
support quantum coherence in photosynthetic organism, also in some cases up to
room temperature, have similarities to microtubules. If quantum effects occur
in microtubules, the authors think that they are similar to those in
photosynthetic organisms.
|
|
