Microtubules are hollow protein polymers from the cytoskeleton, a network of filaments that provides the cell with mechanical integrity and is involved in a plethora of important cell functions. The polymers consists of dimers made of alpha- and beta-tubulin, here shown in red and orange. Dimers form chains called protofilaments, and the protofilaments arrange in a circle to form a tube with a diameter of ~25nm. 
Because of their anisotropic architecture, microtubules have mechanical properties that are a lot more complex than the predictions of simple polymer models. Most significantly, their stiffness depends on their length! Shorter microtubules are actually much softer than measurements on longer microtubules would suggest. The reason is that when microtubules deform, their protofilaments can slide past one another and make the response much softer [Pampaloni, 2006].
The length-dependent stiffness also affects the timescales of microtubule thermal shape fluctuations. Because short microtubules are softer than expected, they also fluctuate more slowly [Taute, 2008] .
Prof. Dr. Erwin Frey ‘ Ludwig-Maximillian University Munich – Arnold Sommerfeld Center for Theoretical Physics
Dr. Francesco Pampaloni ‘ Johann Wolfgang Goethe University Frankfurt – Frankfurt Institue for Molecular Life Science
Dr. Thomas Surrey ‘ Cancer Research UK London Research Institute
NSF grants CMMI-0728166 and CMMI-1031106.