Neurons have a large fraction of stable brain microtubules forming the cytoskeleton of the cell, which provide a mechanical support for the extended dendrites and axonal arborizations and serve as railroads for molecular and vesicular transport. Except for the latter two functions it has been hypothesized that these stable microtubules might also act as quantum or classical computers, the function of which is based on electron hopping associated with kinking of the tubulin α/β-dimer. Hameroff, Tuszyński and others have supposed that the energy needed for such computation could be somehow delivered via cycles of tubulin bound GTP hydrolysis with subsequent GDP exchange for GTP. Here we review the microtubule biophysics and present structural data explaining why the proposed tubulin-bound GTP energized classical or quantum tubulin dimer computation is a fiction and cannot occur in stable microtubules. In addition, we point a flaw in Satarić-Tuszyński ferroelectric microtubule model and show a physical inconsistency in Hameroff-Penrose Orch OR based on the fact that the energy released from a single GTP molecule is 1013 times greater compared to the gravitational energy needed to collapse the relevant number of tubulins for 25 ms.

tubulin, N-site, E-site, GTP, GDP, energy, computation