Final answer:
Option C, 'Two cylinders twist together to form coiled coils,' is not a part of microtubule formation. Microtubules are formed by the stacking of alpha-tubulin and beta-tubulin heterodimers into protofilaments, which then assemble into a hollow cylinder.
Step-by-step explanation:
The process of microtubule formation does not include the step where "Two cylinders twist together to form coiled coils," making option C incorrect. Microtubule formation begins with the non-covalent bonding of alpha-tubulin and beta-tubulin to form a heterodimer. These heterodimers then stack on top of each other through non-covalent bonds to form protofilaments. Thirteen parallel protofilaments come together to form a hollow cylinder, which constitutes the structure of a microtubule. Instead of twisting together to form coiled coils, the structure results in hollow, rigid cylinders that are crucial for cell shape, motility, and cell division processes like forming the mitotic spindle.