Final answer:
The end of the microtubule with α-tubulin exposed is the (+) end, which is the growing end where tubulin dimers are added.
Step-by-step explanation:
The end of the microtubule that has α-tubulin exposed is the (+) end. Microtubules are structured such that they have inherent polarity, with an alpha-tubulin exposed plus end and a beta-tubulin exposed minus end. The dimers of α-tubulin and β-tubulin polymerize into the microtubule's wall, with the plus end generally associated with growth and addition of new tubulin dimers, and the minus end typically being where removal or disassembly occurs. This is an essential feature for microtubule functions in cellular processes like mitosis, where they form the spindle apparatus and are responsible for pulling chromatids apart during anaphase.