Components: Actin is the structural component of microfilaments and exists in two forms, globular actin and fibrillar actin.

Structure: There is a nucleotide binding site and a divalent cation (Mg2 or Ca2) binding site inside the cleft

Assembly process: MF assembly can be divided into several stages: core organization, extension and stabilization.

Cc=Koff/Kon, when the concentration of free actin in the system is higher than Cc, △G is less than zero, and the ends of microfilaments will continue to assemble. When the concentration of free actin is lower than Cc, ΔG is greater than zero, and microfilaments will spontaneously depolymerize.

Treadmill behavior: During in vitro assembly, the positive end of microfilaments lengthens due to the continuous addition of actin subunits, while the negative end shortens due to dissociation.

Features: Dynamic changes in MF are consistent with changes in cell physiological functions. In the body, some microfilaments are permanent structures and some are temporary structures.

Cytochalasin

phalloidin

actin monomer binding protein

nucleation protein

capping protein

cross-linking protein

Cut and depolymerize proteins