Which statement is not correct about microtubules?
1
Microtubules are composed of polymers of the protein tubulin.
2
The tubulin monomer of microtubules is composed of alpha and beta tubulin.
3
Microtubules are solid cylinders with an outer diameter of 25 nm.
4
A single microtubute consists of tubulin monomers arranged in columns called protofilaments