Final answer:
The nucleotide-binding site when tubulin dimers assemble into microtubules specifically binds GTP. This assembly process is essential for the functional roles that microtubules play in cell structure and division.
Step-by-step explanation:
When tubulin dimers assemble into microtubules, the nucleotide-binding site specifically binds guanosine triphosphate, or GTP. Tubulin dimers are made up of α-tubulin and β-tubulin monomers, and the polymerization of these dimers into microtubules is driven by the hydrolysis of GTP. Microtubules are essential components of the cell's cytoskeleton, playing crucial roles in maintaining cell shape, enabling intracellular transport, and facilitating the separation of chromosomes during cell division.
The nucleotide-binding site when tubulin dimers assemble into microtubules is GTP (Guanosine Triphosphate).