Regarding actin I have attached slides to accompany my question When actin binds

Question

Regarding actin I have attached slides to accompany my question When actin binds ADP does it polymerize? When does it polymerize? Does it always have ATP or ADP on it? What does ATP hydrolysis do? Does it convert to ADP? Please answer clearly for this concept Thank you so much SmartArt lapet Text Arrange Q Quick Box Shape Outline A. Rho family GTPase activates WASp/Scar protein > Pool of ProfilinvActin B. WASp/Scars activate Arp2r3 complex - c. Arp2/3 complexes initiate new filaments as branches on old filaments E. Capping protein elongation e Arp3 p34 P21 3 L Profilin binds ADF/cofilin Arp2 G. ADF/cofilin severs and depolymerizes ADP-actinfilaments P16 H. Profilin catalyzes exchange of ADP for ATP p40 A Elsevier Science (USA) items and derived items copyright 2002, Elsevier Science (USA). All rights reserved. Pollard

Explanation / Answer

There are three phases of actin polymerization which includes Nucleation (lag phase; no filament formation), Elongation (growth phase;)and Steady state (equilibrium phase; filaments no longer grow). actin polymerization Begins with nucleation which involves trimer formation. ATP-G-actin monomers add onto the trimer (3 molecules of G-Actin) to polymerize into filaments
More Actin is then polymerized into the seed. Actin Is a globular protein (monomer: G-Actin)
makes filaments (F-Actin) Has two subdomains. It has a cleft at the minus end and a binding site for ATP (or ADP) and Mg2+ in the middle.G-actin ADP is exchangeable for ATP.ATP-bound actin polymerizes.
After polymerization, ATP is hydrolyzed to ADP + Pi inside the filament ADP-actin can also polymerize when at high concentrations (doesn't happen often).Normally, only subunits newly added to the polymer have ATP (on + end)
Hydrolysis of ATP is not required for polymerization as Pi is released slowly, which leads to conformational change, which further destabilizes the polymer, allowing de-polymerization.

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