Mechanical properties of microtubules explored using the finite elements method.

Microtubules (MTs) are complex protein polymers composed of and tubulin dimers which assemble into threads called protofilaments. Between eight and nineteen protofilaments may form a hollow tube of several micrometers long. The most common MTs, 13 protofilament MTs, have a diameter of 24 nm with a wall about 5 nm thick and a hollow central core about 15 nm in diameter. These dimensions are directly related to the number of protofilaments. MTs are one of the main components of the cytoskeleton and play an essential role in many fundamental physiological processes in the cell. They provide mechanical stability and maintain the cell's shape. Inside cells they act as railways along which motor proteins transport vesicles or organelles. During cell division they form the mitotic spindle, which is responsible for separating chromosomes that carry the genetic code. They can also form complex bundles (cilia and flagella) that can propel sperms and some eukaryotic cells (e.g. , Euglena rostrifera). Microtubules assembled inside cells can be decorated with microtubule-associated proteins (MAPs) that can modify their spatial organization and dynamics. Mechanical properties of MTs largely determine their functions. Quantifying the way they resist mechanical deformation by determining their Young's and shear modulus can permit a better understanding of all the vital physiological mechanisms in which MTs are involved. However, measuring and understanding MTs mechanical properties is not a simple task. Two decades of measurements involving different techniques such as optical tweezers, hydrodynamic flow, atomic force microscope (AFM), 11] and persistence length observations, resulted in values of Young's modulus between 1MPa and 7 GPa. 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