The Current Model for the Nucleation of Microtubules Is That

Multiple Choice

The current model for the nucleation of microtubules is that a helical array of gamma-tubulin subunit forms an open,ring-shaped template on which the first row of alphabeta-tubulin dimers assembles.How does this model account for the polarity of microtubules?

A) Only the alpha-tubulin of a heterodimer can bind to the ring of gamma-subunits.
B) Only the beta-tubulin of a heterodimer can bind to the ring of gamma-subunits.
C) The ring structure straightens out the microtubule.
D) The ring structure interacts with a homodimer instead of a heterodimer.
E) Only the alpha-tubulin of a heterodimer can bind to the ring of gamma-subunits.and the ring structure straightens out the microtubule.