DIELECTRIC POLARIZATION, ELECTRICAL-CONDUCTION, INFORMATION-PROCESSING AND QUANTUM COMPUTATION IN MICROTUBULES - ARE THEY PLAUSIBLE

The multitude and diversity of functions performed by the cytoskeleton of eukaryotic cells poses a major scientific puzzle. Microtubules, wh ich are the main components of the cytoskeleton, are engaged in such i mportant activities as material transport, cell motility, cell divisio n, signal transduction and possibly information processing within axon s of nerve cells. The latter aspect has been recently brought to the f orefront of consciousness studies by R. Penrose and S. Hameroff. In th is paper we discuss the potential of microtubules as information proce ssing units from a physical standpoint. In particular, since electric dipoles are a characteristic property of protein molecules, and as suc h may undergo various ordering phase transitions, it can be expected t hat microtubules support the existence of various ferroelectrically or dered states. It is also argued that the piezoelectric effect may link electric and elastic properties of a dielectric polymer system and he nce explain a number of experimental observations both in vitro and in vivo. Furthermore, preliminary results are shown of recent quantum me chanical calculations for the electrical conduction properties of micr otubule protofilaments which support the assertion that the latter may function under certain conditions very much like semiconducting devic es. Indirect evidence links the cytoskeleton with information processi ng and cognitive function. We discuss some plausible ways in which axo nal microtubules can be involved in the functioning of the brain. Fina lly, we present a hierarchy of energy values for a number of physical and chemical interactions of interest and discuss their relative impor tance.