(*) Summary.
Microtubules are the stiffest cytoskeletal component and play versatile
and indispensable roles in living cells. In the conventional view MTs
are seen as internally prestrained but intrinsically straight Euler
beams. There exists, however, a growing number of inconsistencies with
this simplistic paradigm. In this talk I will review the line of
thoughts which brought us to develop a new theory of microtubules based
on the hypothesis that the GDP-tubulin dimer is a conformationally
bistable molecule rapidly fluctuating between a discrete curved and a
straight state. The fundamental result is that MTs spontaneously form
large scale helices of micron size pitches and diameters as a
consequence of a cooperative interaction between its individual
fluctuating subunit. Cooperativity of fluctuating internal degrees of
freedom associated to the rotational symmetry of the MT, apply that MTs
are helices that are constantly but coherently reshaping by thermal
fluctuations. When clamped by one end the microtubules undergo an
unusual zero energy motion. As we will see, this is the key for a
coherent interpretation of certain challenging experimental results not
captured by the previous scenario. We will also discuss possible
implications in vivo.
