Figure 3. A simple model of microtubule growth.

(A) The affinity of loner, corner, and bucket sites at the growing plus-end are exponential functions of the free energy of the underlying lateral and longitudinal contacts (based on Van Buren et al. (2002))²².

(B) As the relative free energies of lateral to longitudinal bonds increases, the growth dynamics transition from “splayed” where protofilaments grow relatively independently, to “tapered” where incorporation predominantly occurs at corner sites, to “barber pole” where the weak longitudinal bond dictates that growth occurs only from corner sites. Accompanying cryoEM-images display a splayed end from McIntosh et al (2018) ⁷¹ and a tapered end from Chretien (1995) ⁵¹.

(C) Different microtubule growth models in the field incorporate very different values for the relative free energy of lateral and longitudinal bonds. Specific parameter values for the different models are presented in Table 1.