Treadmilling of a Microfilament
The animation to the right illustrates the "treadmilling" of actin microfilaments. As you watch the animation, note that the microfilament is becoming longer on the left side (the + side) and shorter on the right side (the - side). Also note that over time, the microfilament appears to slowly move to the left. The microfilament is not actually "moving" in the sense that it would have momentum. It is the "association" between the G actin monomers which form the microfilament which is moving in space and time. The various colors of the G actin monomers used in this animation do not indicate any special characteristics. Rather, the green and gold colors are used so that the observer can better see the twisted conformation of the microfilament. The blue color is used as a reference to better see how the microfilament is elongating on one end and shortening on the other. All of the actin monomers assemble in a defined orientation such that the microfilament has a molecularly defined directionality or polarity. Click here to see an illustration of this polarity. Other molecules in the cell (such as myosin) can read this polarity and can thus interact with microfilaments in directionally specific ways.
Learn about the role of ATP/ADP in microfilament assembly
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