Question

To divide, cells undergo a process called mitosis (discussed in Ch. 18) in which polymers of a protein called tubulin assemble to form microtubules, which are rope-like structures that help separate a cell into two cells during division. The graphic below depicts the polymerization of tubulin into a microtubule. If a cell in mitosis is cooled to 0°, the microtubules depolymerize into tubulin monomers. The same is true for microtubules made from pure tubulin in a test tube; they assemble readily at 37°C, but disassemble at low temperature. This behavior is governed by the basic thermodynamic equation: ∆G = ∆H − TΔS A. Decide what signs (positive or negative) of ΔH and ΔS must be to account for the temperature-dependent polymerization described above, and show how your choices account for polymerization of tubulin at high temperature and its depolymerization at low temperature. (Assume that the ΔH and ΔS values do not change with temperature).