Question

The concentration of actin monomers is high in the cytosol. What keeps these monomers from polymerizing totally into filaments?

A. The concentration is high, but not high enough for polymerization to occur.
B. The monomers are bound by proteins that prevent their polymerization.
C. Not enough of the monomers are bound to ATP.
D. Actin monomers spontaneously polymerize into filaments.

Answer 1

The concentration of actin monomers in the cytosol is prevented from polymerizing totally into filaments due to the binding of ATP to the monomers, which is necessary for polymerization. Once ATP is hydrolyzed, the binding strength is reduced, destabilizing the polymer. Proteins can also bind to the monomers and prevent their polymerization.

Step-by-step explanation:

Actin monomers in the cytosol do not polymerize totally into filaments due to several factors. First, the binding of ATP to the monomers is necessary for polymerization to occur. Once ATP is hydrolyzed to form ADP, the binding strength of the monomers is reduced, destabilizing the polymer. Additionally, proteins can bind to the monomers and prevent their polymerization. These factors contribute to the dynamic and non-equilibrium nature of actin polymerization.