Critical concentration is

A) the concentration of tubulin dimers at which assembly is balanced with disassembly.

B) the concentration of tubulin dimers at which assembly occurs primarily.

C) the concentration of G-actin in most muscle cells.

D) required before nucleation can occur.

E) both choices A and D.

A

Explanation:

Critical concentration is the concentration of tubulin dimers at which assembly is balanced with disassembly, means no net increase or decrease.

The critical concentration is the concentration of either G-actin or the alpha, beta - tubulin complex at which the end will remain in an equilibrium state with no net increase or decrease It occurs when one end of a filament grows or increase and the other end decrease or shrink.