Microtubules are composed of alpha- and beta-tubulin subunits assembled into linear protofilaments. A single microtubule contains 10 to 15 protofilaments (13 in mammalian cells) that wind together ...

In this diagram of G-protein-coupled receptor activation, the alpha, beta, and gamma subunits are shown with distinct relationships to the plasma membrane. After exchange of GDP with GTP on the ...