Final answer:
The nucleation model involving γ-tubulin ring complexes accounts for microtubule polarity by arranging α-β-tubulin dimers with a distinct orientation, leading to a plus end for assembly and a minus end for disassembly.
Step-by-step explanation:
The current model for the nucleation of microtubules explains the polarity of microtubules through the arrangement of α-β-tubulin dimers. Each microtubule has a plus end (+end) where addition of tubulin dimers occurs and a minus end (-end) where disassembly can happen. The γ-tubulin ring complexes serve as a template at the minus end, orienting the α-β-tubulin dimers in such a manner that exhibits the distinct polarity.
Microtubules are dynamic structures mainly composed of α-tubulin and β-tubulin that polymerize to form a hollow tube. Within cells, they provide essential functions such as maintaining cell shape, enabling vesicle transport, and separating chromosomes during cell division. The centrosome, particularly the centrioles within animal cells, serves as the nucleation site during microtubule organization, influencing the direction of growth and thereby establishing the polarity inherent to microtubules.