The G actin are Actin monomers have a nucleotide binding site which accommodates a molecule of ATP where ATP is hydrolyzed after polymerization. The plus end of an actin monomer has a net positive charge. Polymerization of an actin filament occur at the both ends but elongation is faster to about 4-5 times at the plus end than at the minus end. Actin generally polymerizes more rapidly at the barbed end than the pointed end.
The correct answer is option a. "If the actual amount of available ATP-bound G-actin is below the critical concentration at both ends of a filament, then the actin filament will depolymerize".
Explanation:
Actin is the monomeric subunit of most filaments in cells, constituting the the cytoskeleton that brings support and maintains the cells' structure. Actin filament depolymerization is a process that allows for the creation of turnovers in the cytoskeleton and ensures that enough actin subunits are available to produce the filaments. One signal that starts actin filament depolymerization occurs when the actual amount of available ATP-bound G-actin is below the critical concentration at both ends of a filament. This occurs in the opposite direction as well, because the ability of a solution of G-actin to polymerize is given when the available ATP-bound G-actin is above the critical concentration.
It is usually easier to calculate an enzyme's reaction velocity from the rate of appearance of PRODUCT rather than the rate of disappearance of a SUBSTRATE. Enzyme activity is measured as an INITIAL reaction velocity, the velocity before much SUBSTRATE has been depleted and before much PRODUCT has been generated. It is easier to measure the appearance of a small amount of PRODUCT from a baseline of zero PRODUCT than to measure the disappearance of small amount of SUBSTRATE against a background of high concentration of SUBSTRATE.
