Figure 6

Bundle of three parallel microtubules (1, 2, 3): an illustration of the principle of summation of pairwise forces. Regarding the microtubule labeled as (2) this principle can be written as follows: {\overrightarrow{D}}_{12}+{\overrightarrow{D}}_{23}+{\overrightarrow{E}}_{12}+{\overrightarrow{E}}_{23}=0 (3) D…ATRACTIVE dipole-dipole pairwise interactions between two parallel microtubules E…REPULSIVE electrostatic pairwise interactions between two parallel microtubules.