Question

• Describe the process of “treadmilling” in an actin fiber. (1 pts.)

• An experiment is done in which freshly purified actin monomers are incubated and polymerization is followed over time. The kinetics of this reaction are plotted below (red line). Interestingly, when a 1μl drop of week-old actin is added to 100μl of fresh actin the kinetics describe by the blue line are observed. Explain. actin pol.png

Answer 1

G actin monomers polymerize to form actin filaments.Polimerization begins with the assembly of three monomers to form a trimer.Ithastwo ends.pointed end and barbed end.Polymerization takes place at both end to form actin filament.Polymerization is reversible that is monomers can dissociate and associate at both ends.When the concentration of free actin monomers falls below a certain level,barbed end will continue to increase in length but the pointed end will decrease in length.This phenomenon is called treadmilling.The tread milling cycle depends upon ATP.Because the ATP binds to the monomers that are added to the barbed end.Soon after polymerization ,ATP hydrolysis to form ADP resulting in ADP bound monomers to the pointed end.ADP bound actin that is in the pointed end dissociates more rapidly than the ATP bound actin monomers in the barbed end.Thos the mechanism of tread milling.